Download the complete guide to hygiene and infection control getinge

The complete guide to hygiene
and infection control
getinge Academy
CSSU Edition
October 2007
Facts and Features:
World health Organization - Report on Infectious Diseases 2000
Overcoming Antimicrobial Resistance
A Message From the Director-General,
Dr. Gro Harlem Brundtland.
”Since their discovery, antibiotics have completely transformed humanity’s approach to
infectious disease. Today, the use of antibiotics combined with improvements in sanitation, housing, and nutrition alongside the advent of widespread vaccination programmes,
have led to a dramatic drop in once common infectious diseases that formerly laid low
entire populations. Scourges that once struck terror into the hearts of millions – plague,
whooping cough, polio and scarlet fever – have been, or are, on the verge of being controlled. Now, at the dawn of a new millennium, humanity is faced with another crisis. Formerly curable diseases such as gonorrhoea and typhoid are rapidly becoming difficult to
treat, while old killers such as tuberculosis and malaria are now arrayed in the increasingly
impenetrable armour of antimicrobial resistance.
This phenomenon is potentially containable. It is a deepening and complex problem accelerated by the overuse of antibiotics in developed nations and the paradoxical underuse of quality antimicrobials in developing nations owing to poverty and a resultant dearth
of effective health care.
Last year’s infectious diseases report, ”Removing Obstacles to Healthy Development,”
demonstrated that communicable diseases remain a significant cause of disability, are
responsible for continued high mortality and primarily afflict the world’s most vulnerable
populations.
This year’s report focuses on the issue of drug resistance and how this disturbing development is closing the windows of opportunity to treat infectious diseases. By developing
a global strategy to contain resistance and building alliances involving all healthcare providers – countries, governments, international organizations, non-governmental organizations and both the private and public health care sectors – we have an opportunity to
launch a massive effort against infectious diseases that perpetuate poverty. Used wisely
and widely, the drugs we have today can be made available to the world’s poorest to
prevent the health care catastrophes of tomorrow.”
Source: WHO (World Health Organization) website: www.who.int
Infectious diseases – a threat to
prosperity and welfare
Major killer in mankind
The global burden of infectious diseases has a
major impact on all healthcare systems as well as
international prosperity and welfare. Throughout
the history of mankind, infectious diseases have
been one of the largest killers. As recently as the
19th century, the likelihood of dying prematurely
from infectious diseases was as high as 40%.
Antibiotics – important lifesavers
Not until the late 1930s did humanity find a way
to counterattack bacterial infections through
penicillin and antibiotics. For more than half
a century antibiotics have been – and still are
– important lifesavers. With the ever-increasing
development of antimicrobial resistance, the
world population is facing a serious threat to
major achievements in healthcare as well as
the development of modern society and global
economy.
A child in pain can’t learn.
Old diseases in new shapes
By the mid-1960s, confidence in the ability to
fight infectious diseases had become so high
that some professionals were even regarding
infectious microbes as largely conquered. The
reversal and wake-up was sudden and brutal
with the recognition of HIV and all consequences
associated with HIV infection. In the last couple
of decades, people all over the world have been
hearing about major new microbes and older
ones in new shapes.
Increased international contacts
One of the key issues is the ease and frequency
of modern travel. The global population in the
18th century was less than 1 billion versus over
6 billion today. Intercontinental travel is measured
in hours rather than months and in millions of
travelers rather than hundreds. Well over a
million passengers, each one a potential carrier
of microbial pathogens, travel daily by aircraft
to international destinations. Add to this all the
intercontinental transport of food products and
other goods.
Physician in ”protective clothing” from the
Middle Ages.
Rapid transport - for better and for worse.
References:
EFHSS -- European Forum for Hospital Sterile Supply
More and more, infectious diseases form a serious threat to people’s health. Adequate
sterile supply plays an essential role in the attempt to reduce the spreading of diseases
within the health service sector. A series of short articles explains each step in the cycle
of sterile supply as it is performed in most healthcare facilities. This first article describes
an overview of the sterile supply cycle. During the coming year, further descriptions of
each step will be worked out and presented by clicking on the topic title or the image of
the respective step in the illustration above. Detailed information on each topic can be
found in more extensive professional literature and the international standards related to
sterilization.
Read more on EFHSS website: www.efhss.com
As always, the human element determines the quality of the service given. This will always
be the case as far as sterilization procedures are concerned.
Welch JD. The organization of central sterile supply departments. J Clin Pathol 1961
January;14(1):69-75
There is still a need for improvement in the sterilization of medical devices, especially
including: the organization of a CSSD; replacement of manual cleaning processes by
automatic cleaning; organization of advanced training courses for the heads and staff of
the CSSD.
Rohm-Rodowald E, Jakimiak B. Assessment of the sterilization of medical devices-an important challenge to healthcare in Poland. (Article in Polish) Przegl Epidemiol.
2004;58(3):501-10.
Hospitals are advised to have their sterilizers and other equipment professionally checked
in order to make sure that specific procedures for safe handling and decontamination of
used surgical instruments and other medical equipment are available.
Jepsen OB. Infection control: preventing iatrogenic transmission of spongiformencephalopathy in Danish hospitals. APMIS. 2002 Jan;110(1):104-12.
A manufacturer is usually legally liable for a defective product; however, processors are
also viewed as manufacturers. Theatre staff who sterilize and label products are also
liable for ten years.
Hewitson P. Decontamination and the law. A better understanding. Br J Perioper Nurs.
2000 Aug;10(8):405-11.
Modern technology has upset the previous ecological balance between humans and microbes.
The combination of rapid travel times of people
and goods and the incubation time of disease
mean that carriers of infectious disease can arrive and leave any given place long before the
danger they harbor is detectable.
New serious outbreaks will happen
Outbreaks of diseases will occur in geographical
locations, animal species and human populations where the diseases in question previously
Banning birds will not stop avian flu.
have been unusual. There is no need to wonder By January 22, 2007 a total of 269 human
whether we will see new outbreaks. The only cases of avian influenza had been reported
to WHO.
questions are when, where and how…. Examples include HIV, West Nile encephalitis, mad cow
disease (BSE), SARS, and avian flu.
Antimicrobial resistance – a major drawback
Before the advent of antibiotics, infectious diseases caused a very high mortality rate. The
rapid development of antibiotic-resistant strains
of bacteria further heightens the risk that epidemics of ”banal” diseases will be more difficult
or maybe even impossible to treat and control.
In United States alone, antibiotic resisAntibiotic resistance has been observed for al- tance costs between $100 million and $30
most all the known antibiotics and it is becoming
billion annually.
increasingly difficult to develop new ones.
Proper hygiene and infection control is therefore
one of the most important issues in all daily activities both from an individual perspective and
from a general healthcare perspective.
Antimicrobial medications are intended to treat
infectious diseases, whereas hygiene and infection control aim at preventing and avoiding them.
Once humanity loses the possibilities provided by
antimicrobial pharmaceutics, due to increased
antimicrobial resistance, all modern healthcare
achievements will be in vain. Patients undergoing cancer therapy are in great need of antimicrobials, as are patients with transplants, major
surgery, implants, and many other treatments.
This scenario will of course have a great impact
on society’s development and prosperity.
Hand disinfection is the most important
infection control measure.
Modern sterile supply departments/units have an important key function in all types of
healthcare facilities.
With increasing knowledge about the risk of transmission of infection and about hygiene,
all types of care can be provided under safe, hygienic conditions that minimize the risk of
transmission of infection.
A decrease in the incidence of infectious disease also leads to a reduction in the
use of antibiotics. This will save lives, reduce additional suffering and contribute
to minimizing further development of antibiotic resistance.
A decrease in the incidence of infectious disease also leads to lower incidence
of patients with hospital-acquired infections, which will have a great impact on
the care provider’s reputation and economy.
The sterile supply area is therefore one of the most important functions in all
healthcare contexts. Personnel in the sterile supply area have a great responsibility
in several respects.
Supporting functions such as water treatment, air treatment, disposables, chemicals,
transport, storage and traceability are also the responsibility of the sterile supply
function.
Fighting further development of antimicrobial
resistance comes down to avoiding unnecessary
infections – where the key issue is hygiene and
infection control.
Unfortunately, hygiene is seldom recognized
as equally important as, for example, heart
surgery, advanced organ transplants and other
sophisticated medical procedures. Despite
that, infectious diseases, hospital-acquired
infections included, are one of the major causes
for treatment failure which most often can be
avoided if basic hygiene protocols are followed.
For the individual patient, the implications of
heightened resistance to antibiotics are increased
suffering and delayed response to, or failure of,
treatment. The cost to society will also be much Basic hygiene is one of the most important
aspects, not only in hospitals.
greater in terms of prolonged hospitalization,
increased need for care in isolation units and
greater costs for pharmaceuticals.
Proper hygiene and infection control –
simply crucial
From a global perspective, certain characteristics
of modern life present a marked increase in the
risk of transmission of infection on a large scale:
growing populations, rapid population migration,
new megacities and particularly increasing
international contacts and rapid means of travel
(e.g. tourism, international business, import and
export of goods and foodstuffs). Previously stable
relationships (ecology) between microorganisms
and humans have been markedly altered.
Every change in the human condition has
led to adaptation by the microorganisms and
exploitation of the new situation.
The breakthrough in bacteriology in the 1880s is
one of the most important events in the history
of modern medicine. It formed the basis of
understanding hygiene and infection control and
opened ways to prevent and limit the spread of
infections and infectious diseases.
Hygiene, infection control and vaccination
programs are important to ensure that as many
people as possible can enjoy good health.
A decrease in the incidence of infectious
diseases also leads to a reduction in the use of
antibiotics.
Efforts against infectious diseases today
will prevent health care catastrophes of
tomorrow.
Microbiology is one of the most important
areas in modern medicine.
Quantity of microorganisms
(infectious agents) in body system
Concentration (titre) of specific antibodies
against infectious agent in the body system
Infected individuals are the most contagious just before the symptoms appear.
Over 90% of all transmission of infectious disease is from individuals without
symptoms of disease (unknown cases)
Period with infectious agent in body systems.
Individuals are infected.
Period from the moment of contamination until the first symptoms of
disease appear.
Colonization of infectious agent, i.e.
the incubation period.
Individuals are free of symptoms
but most contagious and cannot be
identified.
Period with symptoms of disease.
Infected individuals can be identified
through medical history taking, physical
examination or laboratory tests.
• All patients are potential carriers of pathogenic microorganisms.Infectious
diseases are most contagious before the first symptoms appear.
• Universal precautions are designed to eliminate the risk of transmission of
microorganisms from both recognized and unrecognized sources of infection.
• Universal precautions must be observed routinely in the care of all patients.
• Universal precautions simply means to always consider everyone and
everything to be infected with everything !
Work with hygiene and prevention of infection is important in many varied fields of activity.
Hygiene control is important in health and medical care, dentistry, water supplies, handling of foodstuffs, rearing livestock, restaurants, tattooing, piercing and even in the home,
to name but a few.
The potential of infectious diseases, evolving epidemics and drug resistance to catapult
us all back into a world of premature death and chronic illness is all too real. Our grandparents lived during an age without antibiotics. So could many of our grandchildren. We
have the means to ensure that antibiotics remain effective, and to limit the devastating
effects of emerging life-threatening infections, but we are running out of time. Monitoring,
surveillance and proper infection control are all key issues.
Infection prevention and control are often perceived as being limited to healthcare facilities and to the surveillance and control of healthcare-associated infections. However, the
scope is much wider.
Infection control refers to all policies, procedures and activities that aim to prevent or minimize the risk of transmission of infectious diseases.
General and simple infection control measures are often effective when specific interventions such as vaccination or antimicrobial treatment are not available or failing. Infection
control measures should be seen as an integral and indispensable part of all activities in
modern society.
Everybody infected with everything
Diseases are at their most infectious during their incubation period, i.e. before the first
symptoms appear. Symptom-free carriers of infectious diseases cannot always be identified through medical history, physical examination or laboratory tests. It is therefore
important to work on the principle that everyone we meet and everything we eat can be
carriers of microorganisms which can cause disease. Simply because microorganisms
are everywhere.
Hygiene, infection control and vaccination programs are important to ensure that as many
people as possible can enjoy good health. As in all other contexts, the main rule is to
”think globally and act locally”.
A global view of HIV infection
38.6 million people [33.4‒46.0 million] living with HIV, 2005
2006 Report on the
global AIDS epidemic
Fig 2.4
06/06 e
Regional HIV and AIDS statistics and features, 2004
Adults & children
living with HIV
Sub-Saharan Africa
Middle East & North Africa
South and South-East Asia
East Asia
Latin America
Caribbean
Eastern Europe & Central Asia
Western & Central Europe
North America
Oceania
TOTAL
Adults & children
newly infected with HIV
Adult (15‒49)
prevalence [%]
Adult & child
deaths due to AIDS
23.6 million
2.6 million
6.0%
1.9 million
[20.9 – 26.4 million]
[2.2 – 2.9 million]
[5.3% – 6.8%]
[1.7 – 2.3 million]
400 000
59 000
0.2%
33 000
[230 000 – 650 000]
[34 000 – 170 000]
[0.1% – 0.3%]
[18 000 – 55 000]
7.2 million
770 000
0.6%
510 000
[4.8 – 11.2 million]
[480 000 – 2.1 million]
[0.4% – 1.0%]
[330 000 – 740 000]
620 000
90 000
0.1%
33 000
[380 000 – 1.0 million]
[50 000 – 270 000]
[<0.2%]
[20 000 – 49 000]
1.5 million
130 000
0.5%
53 000
[1.2 – 2.2 million]
[100 000 – 320 000]
[0.4% – 0.7%]
[41 000 – 69 000]
240 000
25 000
1.1%
21 000
[180 000 – 300 000]
[19 000 – 35 000]
[0.9% – 1.5%]
[15 000 – 28 000]
1.4 million
160 000
0.7%
48 000
[950 000 – 2.1 million]
[110 000 – 470 000]
[0.5% – 1.1%]
[34 000 – 66 000]
700 000
22 000
0.3%
12 000
[550 000 – 920 000]
[18 000 – 33 000]
[0.2% – 0.4%]
[ <15 000]
1.2 million
43 000
0.7%
18 000
[710 000 – 1.9 million]
[34 000 – 65 000]
[0.4% – 1.0%]
[11 000 – 26 000]
72 000
8000
0.3%
2900
[44 000 – 150 000]
[ 3900 – 61 000]
[0.2% – 0.8%]
[1600 – 4600]
36.9 million
3.9 million
1.0%
2.7 million
[31.9 – 43.8 million]
[3.3 – 5.8 million]
[0.8% - 1.2%]
[2.3 – 3.2 million]
12/06 e
HIV and AIDS epidemic - global data December 2006.
Source: UNAIDS - Joint United Nations Programme on HIV/AIDS
www.unaids.org
AIDS Epidemic Update
December 2006
Table 1a
Infectious diseases – past and present.
HIV epidemic – the plague of modern society
During the spring of 2002, the World Health Organization (WHO) reported that the HIV
epidemic had exceeded in scale the plague (Black Death) of the 1300s and had therefore
become the pestilence with the greatest mortality of all time.
Acquired Immunodeficiency Syndrome (AIDS) has killed more than 25 million people since
it was first identified in 1981. The AIDS epidemic claimed 3.1 million lives in 2005.
Over 95% of new HIV cases occur in the poorest nations of the world every year and
the disease is spread mainly through heterosexual contact. Sub-Saharan Africa remains
hardest hit – two thirds of all known individuals suffering from HIV live in that area.
HIV epidemic increases risk for other infections
An estimated 40.3 million people are now infected with the human immunodeficiency
virus (HIV). Almost 5 million were newly infected with the virus in 2005.
One of the great risks associated with the HIV epidemic is an increased spread of ”other
common infectious diseases” on a large scale.
International contacts – for better and for worse
Today’s most virulent killers have been at work for centuries. The situation in developing
nations remains as grim as that of previous generations in industrialized nations. Through
extended international contacts, infectious diseases continue to be an ever-increasing
omnipresent threat to life and livelihood.
Infectious diseases have always been there
The scenario is not new to mankind: we have met the devastating threat from emerging
epidemics many times in history. In Europe, wave after wave of epidemics kept humanity
forever teetering on the edge of demographic collapse. Between the 14th and 15th
centuries, the continent saw its population halved by successive outbreaks of smallpox,
typhus, and the ever-present menace of the Black Death (plague).
Microorganisms have and will always play important roles in nature and in history.
Great discoveries have been made the last 150 years within microbiology, but only during the last
decades has the world learned about previously unknown microorganisms, e.g. HIV, West Nile
encephalitis, mad cow disease, SARS, and avian flu.
Previous pandemics in serious variants of Influenza typ A:
1918-1919 Spanish flu A(H1N1): approximately 20-40 million people worldwide, died
from this pandemic, resulting in the highest known influenza-related mortality.
1957-58 Asian flu A(H2N2): 1,000,000 deaths worldwide.
1968-1969 Hong Kong flu A(H3N2): 700,000 deaths worldwide.
Basic hand hygiene together with constant international surveillance and reporting systems as well as early identification of infectious agents are among
today’s most powerful tools to prevent large outbreaks of communicable diseases
Tuberculosis notification rate, 2004
Notified TB cases (new
and relapse) per 100 000
population
0 - 24
25 - 49
50 - 99
100 or more
No report
Source: WHO
Isolation – a barrier technique introduced in ancient history
The shaking chills Alexander the Great suffered in his last illness while campaigning in
Mesopotamia in the 4th century B.C. may have been due to malaria. In Mesopotamia it
was believed that diseases were caused by spirits having possessed the body. To avoid
transferal of the offending demon to others, the afflicted person was avoided as much
as possible – an early form of isolation, later carried over to the Hebrew culture where
the taboo against touching a sick person became a key factor in the system of public
hygiene.
Cleaning and disinfection – already known in the old world
Already at that time, Aristotle instructed Alexander the Great to require his armies to boil
their drinking water and bury their feces.
The Jewish Talmud precept that “Physical cleanliness is conducive to spiritual purity”
resulted in regarding a leper, for instance, as unclean and his/her clothing was to be
burned.
For religious reasons the ancient Egyptians paid much attention to the cleanliness of
body and home; washing was practiced every morning, evening and before each meal.
Since soap was not yet known, a type of alkali was used.
Hygeia the goddess for prevention of disease
In Greek mythology, Chiron, the centaur, taught Asclepios all there was to know about the
healing arts. Asclepios’ daughter Hygeia was the deity of health who came to represent
prevention of disease.
Disinfectant already used by Odysseus
The first written report on disinfectant is found in the Odyssey by Homer, 700 BC. When
Odysseus, returning home after a long absence, killed his wife’s suitors and had disposed
of their bodies, he turned to his old nurse and said “bring me some disinfectant sulfur, and
make me a fire so that I can fumigate the house”.
Sulfur dioxide is still used as a disinfectant and preservative for dried fruit, fruit juices and
wine.
Influenza – an ever-returning virus in new shapes
In the autumn of 1918, by the end of the First World War, a tidal wave of influenza rolled
over Europe, Asia, Australia, North and South America, wiping out an estimated 20 – 40
million people worldwide and devastating entire economies. Since then, the world has
seen two more influenza pandemics, though not so devastating. The annual influenza is
an often-forgotten major killer with a death toll of at least 1 million every year.
Flu pandemics are global epidemics of a newly emerged strain of flu (a new influenza A
subtype). At the year 412 BC, a disease with symptoms that today would be diagnosed
as flu, was first mentioned by Hippocrates. The fist time a worldwide pandemic has been
described is in the year 1580. Between the years 1580 - 1900 there were 28 known flu
pandemics.
The annual return and new variants make influenza virus type A one of the world’s
biggest killers!
Infectious diseases – a devastating warlord
Napoleon cannot blame the Russians – or even on the Russian winter – for his retreat
from Moscow. His deadliest opponent by far was typhus, a louse-borne infection that reduced the healthy Grande Armée of 655 000 to a pitiful and demoralized band of 93 000
– who wound up straggling home and surviving just long enough to pass the disease on
to neighbours and loved ones. The subsequent epidemic killed another two million.
Smallpox and measles enslaved the Amerindians
In the New World, it was not the superior Spanish armada that resulted in the conquest
and enslavement of the Amerindians. It was rather the allies of the conquistadors that
conquered – smallpox, influenza and measles –formerly unknown in the Americas. In the
space of 10 years, historians estimate that Mexico’s population decreased from some 25
million to 6.5 million owing to epidemics of infectious disease – a drop of 74% !
It has been described that the Spaniards were astonished by the sophisticated drainage
systems for disposal of wastes and the public latrines in the Aztec capital Tenochtitlan – a
clean, prosperous and healthy city.
Smallpox has an overall fatality rate of 30%. The last naturally occurring case in the world
was in Somalia in 1977.
The first accurate description of smallpox and measles was written by the Persian Rãzi
(abu-Bakr Muhammad ibn-Zakariyã al-Rãzi, 850 – 923). He recommended simple rather
than complex remedies, such as proper food in preference to drugs in treatment. Today
we know that proper nutrition is one of the key issues in maintaining a well-functioning
immune system.
By the 1600s, colonizers in North America knew enough about epidemiology to maliciously inflict deadly diseases on locals by providing ”gifts” of blankets and clothing infested
with smallpox and typhus-bearing lice – the first recorded acts of biological warfare.
Early vaccination in Africa and China
There were methods of preventing diseases – not just ceremonial and religious methods
– even in primitive societies. Long before the colonial period in Africa, some tribes practiced variolation, i.e. inserting fluid from smallpox blisters under the skin in order to produce
a mild form of the disease while protecting from severe illness. In some parts of Asia,
smallpox scabs in water were pricked into the skin, and the Chinese were known to blow
powdered scabs into the nostrils.
Vaccination against smallpox was introduced in Europe with the famous paper of Edward
Jenner in 1798, inoculating humans with the fluid from cattle diseased with cowpox.
The New World revenge – syphilis
If smallpox was Europe’s primary export to the New World, the New World may well have
hit back with syphilis.
The disease was untreatable until 1910 when Ehrlich together with Hata developed Salvarsan as a medication for syphilis.
Salvarsan is based on synthesized derivates of metallic substances and arsenic. Already
in the 17th century the Chinese physician Chu-Szi-sung reported the use of arsenic and
metallic substances as therapies for venereal diseases, although not well differentiated.
Syphilis, sive morbus Gallicus
In 1530, to express his ideas on the origin of syphilis the Italian physician Girolamo Fracastoro wrote the poem Syphilis, sive morbus Gallicus (Syphilis, or the French disease).
In the verses Syphilus (”pig-lover”), a typical pastoral name for a shepherd, is struck by
the disease syphilis for having offended Apollo.
A shepherd once (distrust not ancient fame)
Possest these Downs, and Syphilus his Name;
Some destin’d Head t’attone the Crimes of all,
On Syphilus the dreadful Lot did fall.
Through what adventures this unknown Disease
So lately did astonisht Europe seize,
Through Asian coasts and Libyan Cities ran,
And from what Seeds the Malady began,
Our Song shall tell: to Naples first it came
From France, and justly took from France his Name.
(Translated from Latin to English by Nahum Tate, 1652-1715)
Living particles causing disease
Giralamo Fracastoro is generally given credit for being the first to recognize the existence
of tiny living particles that cause disease by being spread by direct contact with humans
and animals and by indirect contact with objects. Fracastoro was anticipating, by nearly
350 years, one of the most important turning points in biological and medical history
– the discovery of microorganisms and the consolidation of the germ theory of disease
by Louis Pasteur and Robert Koch in the late 1870s.
During the 16th century the two venereal diseases syphilis and gonorrhea were directly
responsible for the suppression of communal baths, this also meant a loss of the only
convenient means of personal hygiene.
Bad air, mala aria, causes serious diseases
The idea that infection is spread by air was described already in the second century A.D.
The Roman Marcus Varro advised against building houses near bogs and marshes “”because there are certain minute creatures which cannot be seen by the eyes, which float in
the air and enter the body through mouth and nose and there cause serious disease”.
The first to see the small creatures
After studying sour milk and vinegar in an early and very simple microscope, the German
Jesuit Athanasius Kircher (1602 – 1680) reported that they contain little “worms” and that
blood from those who have died of pestilence contains “infusion animals”.
The Dutch naturalist Antony van Leeuwenhoek (1632–1723.) ameliorated the microscope
by using more powerful lenses. Leeuwenhoek showed that microorganisms exist in dental plaque (which was then called material alba) and in sewage. The scarce possibilities
for microscopy and the theoretical concepts that existed on microorganisms resulted in
finds that were both imaginative and speculative. Leeuwenhoek called his finds “animacules” (little animals).
Mansur Hospital in Cairo
During the Middle Ages the best-known hospitals were in Bagdad, Damascus and
Cairo. The largest and most magnificent was the Mansur Hospital in Cairo, founded in
the 13th century. The hospital had separate wards for different diseases such as fever,
eye conditions, diarrhea, female disorders and convalescents.
A war in Crimea – the start of the Black Death
In the year 1347 the city of Caffa in the southeast Crimea was besieged by fierce Tartars. The Tartars catapulted corpses of soldiers who had died from plague into the city.
When traveling home, the Christian defenders when travelling home started an epidemic which quickly spread throughout Europe. By 1352, twenty-five million, 25% of the
population of the continent had died from the disease. In his book Decameron, Giovanni Boccaccio writes “either because of the influence of the planets or sent from God as
a just punishment for our sins”. He also suggests “keeping the city clear from filth and
excluding all suspected people”.
Cholera not believed to be contagious until 1892
In 1783, British historians calculated that some 20 000 pilgrims to the Indian holy site
of Hardawar succumbed to cholera. Within months the bacilli spread outwards towards
China, north to Russia and southwest to the Middle East.
By 1831, cholera infected nearly half of the Haj faithful making the annual pilgrimage
to sacred sites in Mecca and Medina – the fatal consequence of drinking from a single
ritualistic source of contaminated water. Dehydrated and shedding vibrios, dying pilgrims crept homewards depositing bacteria along key transportation routes. The great
ports of Alexandria and Istanbul were soon staggering under a cholera epidemic that
subsequently radiated outwards throughout North Africa, into the Balkans, up along
the Danube and onwards towards Hungary leaving behind a trail of corpses, orphans,
economic ruin and contaminated water and food.
Despite this, according to the the general opinion in the middle of the 18th century,
cholera was not infectious. However, Dr. John Snow in London showed in around 1850
that cholera is spread by polluted water. His views on this subject were not generally
accepted until after the epidemic cholera in Hamburg-Altona in 1892. Both cities took
their water from river Elbe, Hamburg directly but Altona after purifying. In Hamburg suffered a severe epidemic but in Altona there were only a few sick people.
Hand hygiene “discovered” 150 years ago
In the early 1800´s, outbreaks of puerperal sepsis – a streptococcal infection – were responsible for the deaths of up to 70% of the new mothers. Already in 1846, the Hungarian surgeon/doctor Joseph Ignaz Semmelweis discovered the importance of hand
hygiene, thirty years before the works of Koch and Pasteur.
Listerism and the golden age of microbiology
The English surgeon Joseph Lister was inspired by the work of Pasteur. In 1867 he
published an article in the prestigious magazine “The Lancet”, describing how patients
during surgery were sprayed with carbolic acid to prevent bacteria from colonizing in
operation wounds.
The Golden Age of Microbiology started after the findings made by Louis Pasteur and
Robert Kock. By 1900, microorganisms known as bacteria had been described and recognized as the cause of numerous diseases such as anthrax, diphtheria, tuberculosis,
cholera, tetanus, leprosy, epidemic meningitis, gonorrhea, brucellosis, abscesses, food
poisoning and dental caries.
Virus – the greatest threat to humanity
In 1892, the Russian microbiologist Dmitri Ivanowski, and in 1898, the Dutch botanist
Martinus Beijerinck, discovered infectious agents that could pass through bacteria-stopping filters. Too small to be seen with the conventional microscope, these agents were
described as ”filtrable viruses.”
Loeffler and Frosch demonstrated in 1898 that agents smaller than bacteria caused footand-mouth disease in animals. Not until 1940 the electron microscope was developed
and Stanley at the Rockefeller Institute published the first picture of virus, first described
as a large protein molecule. Since then a large number of viruses have been isolated and
analysed through electron microscopes.
Joshua Lederberg, the Nobel Prize Laureate of Physiology and Medicine in 1958, maintained a long time ago that viral diseases are the greatest threat against humanity, and his
prediction seems to be coming true.
When everything was thought to be safe …
In 1977, smallpox was deemed to be exterminated. It was a victory over a deadly virus,
and it was considered only a question of time before the rest of the deadly infections were
to be annihilated by modern science. Nobody could imagine that an up to now unknown
virus was spreading and that in a few years HIV would be a worldwide epidemic.
Since then, we have also been forced to learn the names of two much dreaded so called
filoviruses, i.e. the Ebola and the Marburg viruses, both with a deathrate of up to 90%.
It is also possible today to identify viruses that were unknown to exist. Prions or proviruses are contagious agents that are not even viruses but only chains of protein. One such
is a very rare and serious disease, the disease of Creutzfeld-Jacob´s disease (CJD), which
slowly destroys the brain tissue.
During the middle of the 1990´s, prions were found in cattle in the form of Bovine Spongiform Encephalopathy (BSE). It differs from the original disease and is therefore called
new variant Creutzfeldt-Jacob´s Disease (nvCDJ). The largest part of the nvCDJ-cases
have been identified in the UK, and reports hint that the disease has been transmitted via
contaminated beef.
Further progress must be based on the simple recognition that humans, animals, plants,
and microbes are all cohabitants of the planet.
Microorganisms are actually more beneficial than harmful to mankind. Their harmful activities are usually the result of microorganisms being someplace they should not be,
growing for some reason out of control.
By the year 2003 the world population suddenly learned about SARS (Severe Acute
Respiratory Syndrom). Corona virus, a virus well known to cause upper respiratory tract
infections, now in a new strain able to cause lower respiratory infections.
SARS caused more fear and social disruption than any other disease of our time. While
it killed a relatively small number of people, it nevertheless had a great impact on economies, international trade and travel.
SARS was stopped by global cooperation. Through meticulous surveillance and transparent information led by the WHO, almost every single case was tracked down. The index
cases could be traced back to what was probably nine people taking the same lift at the
Hotel Metropole in Hong Kong. Once the spread of disease was admitted, it proved an
excellent example of international cooperation and the importance of constant surveillance and reporting systems.
Traceability, deviation reports and analysis, epidemiology and quality assurance are all
important in infection control.
Ecology and evolution
Instabilities arise from two main sources loosely definable as ecological and evolutionary.
Ecological instabilities arise from the ways we alter the physical and biological environment and our interactions (including hygienic and therapeutic interventions) with parasites.
Evolution alters the ways humans and microbes are able to adapt to new
environments, but due to the fast turnover in new microbial generations (minutes) compared with human generations (several decades), we will always be behind.
The first approach to preventing disease transmission is to keep microorganisms in their
proper place by preventing contamination. If they should get somewhere they should not
be, they should be removed, killed or kept from growing to harmful numbers. Intervening
should be carried out with the following priorities: cleaning, growth inhibition, disinfection,
sterilization, surveillance, isolation, immunization and, if these measures are not successful, by antimicrobial therapy.
Heat is a simple way to destroy microbial life. In biblical and medieval times heat in the
form of fire was used to destroy clothes and corpses of diseased persons. In 1776 Spallanzani wrote that microorganisms could be killed by heat, but that some organisms were
more resistant than others. To kill these resistant ones, the liquid had to be boiled for 1
hour. In 1831 William Henry showed that cowpox used for smallpox vaccine was inactivated at +140°F (+60°C) after 3 hours but was still active at 120°F (+49°C).
Both Spallanzani and Henry had shown sterilization and disinfection by heat as they are
still being used today; however their work was ignored and forgotten until 1881 when Robert Koch published his findings on the relative values of hot air and steam as sterilizing
agents.
John Tyndall discovered the benefit of discontinuous heating (Tyndallization) and Pasteur
the sterilizing effectiveness of superheated steam. Together with the principles of Papin’s
digestor (or engine for softening bones) from 1681, this was the base for modern sterilizers. Sterilizers for laboratory use under the name of Chamberland’s autoclave were
made by the Parisian engineering firm Weisnegg from about 1884.
Today, sterilization by moist heat in the form of saturated steam under pressure is by far
the most reliable medium, known for the destruction of all forms of microbial life. Steam
sterilization is the most economical and effective method of sterilization.
In 1968, E.H. Spaulding introduced the classification of surgical instruments into noncritical, semi-critical and critical in accordance with their intended use. Critical items are
defined as any objects that enter sterile tissue or the vascular system and must therefore
be sterilized.
Today we now know about the existence of infectious agents, prions, where
small resistant subpopulations can even survive a sterilization process at
134° C (273° F) for 18 minutes. We also know that bacterial endotoxins are
able to cause severe inflammatory reactions.
The importance of proper cleaning and disinfection prior to sterilization can
not be overlooked. Standard methods of sterilization, such as autoclaving or
sterile filtration, have little effect on endotoxin levels.
Together with increased antimicrobial resistance and even bacteria that are
able to destroy antibiotics, to be able to succeed we are back to the basic
principles described so many times in history – the importance of cleaning
and limiting outbreaks of disease through surveillance, isolation and destruction of infected material by heat.
Short biographies:
Chun Szi-sung, Chinese physician ,17th century, wrote “The Secret Therapy for The
Treatment of Venereal Diseases”, where he reported using arsenic against these diseases.
(A treatment developed 300 years later in the west by Paul Ehrlich.)
Ehrlich, Paul, 1854 – 1915, Nobel prize winner (with Ilya Ilyich Mechnikov) 1908 “in
recognition of their work on immunity” . His dissertation was written on the theory and
practice of staining animal tissues.
In 1882 Ehrlich published his method of staining the tubercle bacillus that Koch had
discovered.This method was the basis of the subsequent modifications introduced by
Ziehl and Neelson, which are still used today. From it was also derived the Gram method
of staining bacteria so much used by modern bacteriologists.
Ehrlich later devoted himself to chemotherapy, basing his work on the idea, which had
been implicit in his doctoral thesis written when he was a young man, that the chemical
composition of drugs used must be studied in relation to their mode of action and their
affinity for the cells of the organisms against which they were directed. Ehrlich and his
assistants (among them Hata) proved that the arsenical drugs they named Salvarsan and
Neosalvarsan were effective against syphilis, but they had to battle with much opposition
before the drugs were accepted for the treatment of human syphilis.
Fleming, Sir Alexander, Ernst Boris Chain and Sir Howard Walter Florey won
the Nobel Prize of 1945 for “the discovery of penicillin and its curative effect in various
infectious diseases”.
In 1928, when Fleming was experimenting with pyogenic bacteria of the
staphylococcus group, he noticed that, around a spot of mould which had chanced
to contaminate one of his cultures, the colonies of bacteria had been killed and had
dissolved away. The mould was of the family Penicillum notatum, and the active
substance was later called penicillin.
Ernst Boris Chain and Howard Florey studied antibacterial substances that had been
produced by microorganisms. These studies led to renewed research of penicillin and
to the discovery of how to use it clinically.
Fracastoro, Girolamo, c. 1483 – 1553, Italian physician, poet, mathematician and
astronomer. He proposed that infectious diseases spread through very small particles, too
small to be seen, which he called “seminaria”. His germ theory of disease was presented
300 years before Louis Pasteur and Robert Koch had formulated it empirically. He was also
the first to describe correctly the clinical implications of typhoid fever. Fracastoro became
famous for his poem Syphilis sive Morbus Gallicus (Syphilis or the French Disease), after
which that disease is named.
Koch, Robert, 1843 – 1910, German physician, Nobel Prize winner 1905 for his discoveries
in relation to tuberculosis. He studied microorganisms, especially anthrax, while working
as a country physician. Later, he not only discovered the causes of many illnesses such
as wound infections, cholera, and sleeping sickness, advanced the method of steam
sterilization, introduced effective preventive measures in typhoid fever, plague and malaria
but he also isolated the tubercle bacillus. His work revolutionized bacteriology.
Lederberg, Joshua, b. 1925, Noble Prize 1958 “for his discoveries concerning genetic
recombination and the organization of the genetic material of bacteria”.
His lifelong research has been in genetic structure and function in microorganisms. It
showed among other things that mutations in bacteria have the same characteristics as
mutations in other organisms.
He has been actively involved in artificial intelligence research (in computer science) and in
the NASA experimental programs seeking life on Mars. He has also been a consultant on
health-related matters for government and the international community. The focus of his
research has now shifted to ”What is the fastest rate possible for the growth of a bacterial
cell, (and why?)” .
Lister, Joseph, 1827 – 1912, British physician. When working at the University of Glasgow, he observed that fractures where bone was exposed through broken skin usually
got infected, whereas fractures that had not broken the skin did not. He concluded that
particles in the air were the cause and called them “disease dust”. In 1860 he became
familiar with the theories of Louis Pasteur and started spraying his patients with carbolic
acid during operations, which reduced the death rates at the Glasgow Royal Infirmary
from 45% to 15% .
Due to the resistance of British and American doctors it took another decade before his
treatments were generally accepted.
Leeuwenhoek, Antonie, 1632 – 1723, He studied microorganisms, which were then
totally unknown. He was the first to observe bacteria and protozoa. He succeeded in
making microscopes, the strongest of which had a magnifying effect of 500 times and a
resolution of 1,0  .Not until the 19th century could better microscopes be made. When
studying semen, Leeuwenhoek launched the theory that conception is the result of a
sperm penetrating an egg. He also discovered the red blood corpuscles.
Nightingale, Florence, 1820 – 1910, British health care reformer, researcher, the founder of trained nursing as a profession for women.
During the Crimean war, reports about the abominable conditions for the wounded in the
field hospitals were frequent, and the minister of war demanded that Ms. Nightingale and
40 other nurses take care of the situation. The death rates at the hospital consequently
sank from 50-60 % to 2%.
Back from the war, Ms Nightingales interest in the Indian health care resulted in the first
health laws in India. It was greatly because of her that nursing was transformed from a
low, unpopular occupation to a highly respected one.
In the Crimean War she was responsible for hospital care of wounded British soldiers - at
first Florence Nightingale met conditions with overcrowded hospitals, lack of hygien and
equipment and poorly feed soldiers. The mortality rate was over 40% in the field hospitals.
Her presence and genius during the war 1854-1855 saved the hospital from total from
demoralization.
Florence Nightingale behind transforming nursing from a low unpopular endavour to a
highly respected part of the healing art.
”The art is that of nursing the sick. Please not not nursing sickness...”
Pasteur, Louis, 1822 – 1895, French chemist, one of the greatest scientists ever.
Early in his carreer he proved that there were two kinds of tartaric acid crystals and that
bacteria acted differently on the two kinds. This lead him to the discovery that microorganisms were responsible for fermentation, and he invented the process called pasteurization (i.e.to heat a liquid to a particular temperature and then cool it in order to kill the
harmful bacteria. The process is mostly used on milk, but Pasteur first used it on wine).
He found that cultures of chicken colera organisms were harmless when injected into
healthy fowls. He used his knowledge to develop cultures of the antrax bacillus which
he treated in different ways. His research showed that when the bacilli had grown in a
particular temperature range, they could be injected in healthy animals, making them resistant. To prove this, he arranged a public demonstration in 1881, where virulent cultures
of antrax bacillli were injected into two groups of sheep: sheep that had already been vaccinated and sheep that had not. The vaccinated sheep all lived and the others died.
In his youth, Pasteur was a promising pastel painter.
Semmelweis, Ignaz Philipp, 1818 – 1865, doctor’s degree in 1844. Head of one of
the two birth clinics in Vienna. The number of women who died of puerperal fever at one
of the clinics was as high as 13%, and at the other one only 2%. The only difference
between the two clinics was that at the first clinic doctors-to-be/students of medicine attended the deliveries, often coming directly from an autopsy, but at the second clinic this
was done by midwives. This difference between the two clinics was generally known, and
it was supposed to be caused by the association with the hospital and by some unknown
factor, depending on bad atmospheric conditions.
During an autopsy, Semmelweis colleague Jakob Kolletschka cut himself and rapidly
developed a high fever and blood poisoning – the same symptoms as the women being
delivered at the first clinic showed.
Semmelweis deducted that “corpse particles” were transmitted from the department of
autopsy to the maternity ward. He thereafter initiated that all doctors and students had to
wash their hands before entering the maternity ward to get rid of the ”corpse particles”.
Boards with the following notice were attached to the entrance of the ward:
”All students and doctors visiting the maternity ward in order to examine patients must
wash their hands thoroughly in the chlorine solution placed conveniently by the entrance
of the ward. Between examinations hands are to be washed with soap and water.”
These precautions eventually resulted in the death rates at the two clinics becoming almost equally low – 1.27% and 1.34% respectively. In spite of the good results, the head
of the hospital, professor Joseph Klein, was decidedly against Semmelweis’ ideas, and
prohibited them from being used at the hospital. He also did not extend Semmelweis’
appointment, which forced Semmelweis to leave Vienna for Budapest, where he became
the head of a maternity ward.
In Budapest Semmelweis conducted a 6-year study, in which he showed that the death
rate due to puerperal fever at this maternity ward was 0.85%. Some years later Semmelweis was made a professor of obstetrics at the University of Pest, where he continued his
work and managed to cut the death rates to a mere 0.39%!
Semmelweis was eventually admitted to a mental hospital. He was discovered to have
an infected wound on one of his fingers, acquired during a gynaecological operation. In
spite of all efforts to stop the infection, Semmelweis developed serious blood poisoning
which led to his death at the age of 47. It is a tragic irony that Semmelweis died from the
disease he had devoted his life to fight.
Semmelweis met with opposition from fellow scientists, which resulted in his being more
and more frustrated and eccentric, and he made enemies among almost everyone in the
academic hierarchy. The death rate at several European maternity wards was as high
as 26% and the studies of Semmelweis were a dangerous proof that it was the doctors
themselves who caused the high death rates
In a letter to professor Scanzoni in Würtzburg Semmelweis writes:
“Your teaching that the epidemic puerperal fever in Würtzburg depends on unknown atmospheric influences or puerperal miasma, is false …
I have an unyielding resolution to end this murdering as best I can …
I condemn you before God and the whole world as a murderer and in all future you will be
known as the Nero of medicine.”
It was not until 14 years after Semmelweis’ death, in 1879, that his ideas started to be
acknowledged when the works of scientists like Joseph Lister, Louis Pasteur and Robert
Koch supported Semmelweis’ finds with their own reports.
Tyndall, John, 1820 – 1893, Irish physicist, after whom the Tyndall-effect is named. Tyndall discovered that light can spread, due to microscopic particles like smoke or dust, so
that a light-beam can be seen in an otherwise dark room.
John Tyndall also had another process named after him: tyndallization, a process of heat
treatment for killing microorganisms. The medium is heated to less than sterilization temperatures, then left to cool so that the spores that were not killed can incubate. This is
repeated for several days to destroy all vegetative forms and germinated spores.
Moist heat in the form of saturated steam under pressure, is by far the most reliable
medium, known for the destruction of all forms of microbial life.
Above, to the right, one of the first manufactured steam sterilizers.
To the left a modern, fully automatic steam sterilizer
Cleaning, disinfection, sterilization and sterile wrapping are also among the most important
“barrier techniques” breaking the mode of transmission. The purpose of sterile wrapping
is to keep articles free from contagious agents until the moment of use.
Since microorganisms are more or less everywhere, it is important to protect individuals
prone to infection by creating barriers that the microbes cannot cross.
This is the very basis of cross-infection control, mostly referred to as “basic hygiene regimes” or “universal precautions”.
A. Remove the infectious agents from the individual or source. This requires antibiotics or
other antimicrobial agents or procedures.
B. Create visible or invisible barriers, e.g. defined areas in the CSSU.
C. Break the mode of transmission by sterilizing instruments and articles
D. Set up barriers at the point of use, e.g. sterile wrapping
E. Make the patient less susceptible through immunization (vaccination) programs and
creation of a healthy and clean environment.
Microorganisms – many different and microscopic forms of life
Microorganisms – friend or foe
Microorganisms occur everywhere, in soil, dust, the air, water, on our clothes, mucous
membranes and skin. Most living things are microbes, organisms not visible to the unaided eye; the organisms that are visible are a small minority. Microorganisms interact with
all members of the living world and much of the inanimate world. Microorganisms play
an important role in the life of earth. In nature, microorganisms participate in the decay of
plants and animals. They are used in the food industry in the preparation of cheese, yoghurt, beer and wine. In water treatment plants, microorganisms are used to break down
organic pollutants in waste water.
The microorganisms that are always present on and in the skin and on all mucous membranes of the entire gastrointestinal tract are usually referred to as the normal flora. Our
normal flora plays an important role in protecting the body from invasion of disease-causing (pathogenic) microorganisms.
Of thousands of known bacterial species, only relatively few cause disease in humans.
However, under certain conditions, even the human normal flora can cause infections.
Microorganisms needs transportation
Microorganisms cannot move independently to any great extent, but exploit particles in
the atmosphere, e.g. dust from clothes, drops of moisture from sneezing. Microorganisms are to be found primarily on upward-facing horizontal surfaces.
Survival of the infectious agent on surfaces such as floors, tables and doorknobs varies
from a few hours for bowel bacteria, to some weeks for staphylococci to several months
for Hepatitis B and rotavirus. Even if viable microorganisms can be found on surfaces in
a room, this is more an indication that a source of infection (infected person) has been in
the area and is seldom an infection risk because the number of microorganisms that may
be transmitted to another individual is not usually adequate.
The tip of two dental rootcanal files. Instrument intended to remove the diseased dental
pulp tissue from rootcanal. Both rootcanal files are sterilized in vacuum steam sterilizers.
Upper picture: The instrument has not been cleaned prior to sterilization - biofilm with
dead tissue and dead microorganisms. Toxins from bacteria in biofilm will cause inflammation.
Lower picture: The instrument cleaned in an ultrasonic cleaner, followed by processing in
a washer disinfector before sterilization.
The rapidly increasing profound knowledge
of microorganisms and the possibilities
to carry out sophisticated medical and
surgical procedures will continuously put
new demands on personal competence
and skills as well as continuous
development and improvement of medical
devices.
Patient safety must always be the number
one priority !
Continuous ecological development between host and microbe
The general health of the host, his or her previous contact with particular microorganisms,
past medical history etc. are significant determinants of infectious disease.
Identifying and preventing infectious microorganisms from causing harm can be compared to the security control at airports: Most microorganisms are friendly and play a very
important role in life on earth, but a few of them are “terrorists”.
Microorganisms, even our own indigenous flora, given the right opportunity can cause
disease. In all healthcare it is of great importance to take measures to stop the “terrorists”
and at the same time cause as little harm as possible to the friendly microorganisms,
to the people involved (patients, personnel and others) and to the surrounding environment.
No hard and fast rule divides microorganisms into clear-cut categories of harmless, commensal organisms and pathogenic species. A common misconception is that an individual who is infected with a pathogenic microorganism rapidly develops symptoms and
becomes acutely ill after an incubation period of 24 to 48 hours. In fact, only a small
fraction of individuals will actually develop disease after exposure.
Microorganisms can lead either to clinical disease (with symptoms) or sub-clinical disease
(without symptoms) or just simply to the recipient being colonized by the infectious agent
without developing the disease. It is important to understand that all colonized individuals
are potentially contagious and will cause further spread of the infection.
For these reasons, a profound knowledge in microbial forms of life and their interaction
with the human system must form the basic concept within infection control in all healthcare settings.
Important facts and features concerning bacteria in sterilization units.
One of the major differences between bacteria and virus is that bacteria can live in almost
any environment. Since bacteria have their own metabolism and ability to reproduce,
they can live under many different conditions and are not dependent on a harboring host
to the same extent as viruses.
Bacteria can therefore exist on surfaces, wrapping materials, clothes, linen, in dust etc.
Viruses needs a living cell (human, animal or herbal) to multiply. For this reason, viruses
will only be found where there is biological material.
Most bacteria are not disease-causing, and only a small fraction of all known bacteria are
harmful in their normal stage. However, many kinds of bacteria are harmful if given the
chance, and are therefore referred to as opportunistic pathogens.
Normally harmless bacteria can be of danger for persons with immunodeficiencies. This
can also be the case if bacteria ends up in an environment or area which is not the
natural place for a specific species.
Immunodeficiencies can be either general, such as in patients with AIDS, or
local immunodeficiencies. A wound should always be treated as an area of local
immunodeficiency during the period of healing.
In the sterilization unit it is not only important to sterilize the medical devices but especially
to make sure that all items will maintain sterility during storage and until the point of
use.
Sterile wrapping are crucial. Most wrapping material allows the steam during sterilization
to enter while the wrapping is wet. The humidity opens the porosity in the wrapping
material and this closes again when the material is dried. If the wrapping material
is wet, the package must thus be regarded as open.
Facts:
- A wet package after sterilization allows bacterial penetration.
- MRSA (methicillin-resistant Staphylococcus aureus) has been demonstrated to
survive on sterile goods packaging for more than 38 weeks.
Clothing and personal hygiene are important:
- Clinical clothing can transmit 50 times more contagious material than airborne
particles.
- MRSA (Methicilin Resistant Staphylococcus Aureus) can survive up to six weeks
on clinical clothing and still be contagious.
- Microorganisms penetrate more easily if clothing is wet.
- Plastic aprons reduce contamination of clinical clothing about 30 times.
Bacteria – basic facts
Bacteria function as independent units. They have a genetic code (deoxyribonucleic acid,
DNA) and distinctive features that are characteristic for living organisms, such as metabolism, irritability and the ability to reproduce.
All living functions of the bacteria are contained within the one cell, in contrast to multicellular organisms such as the human body, where greater or lesser specialization may
occur in different types of cell. Different kinds of antibiotics affect the bacterial cell and its
metabolism, but not human tissue.
Bacteria may be found on all kinds of tissue, both living and dead.
The size of a bacterial cell varies between 1 - 20 mm (1 mikrometerr = 1/1000th of a mm),
depending on whether they are cocci (round) or rods. For comparison a red blood cell is
at least 7 mm.
To survive and multiply, bacteria absorb substances from their surroundings and can
therefore form enzymes and toxins. Toxins can take the form of exo- or endotoxins.
Exotoxins are poisons excreted by living bacteria. The endotoxins are often remnants of
microorganisms, parts of the cell walls or poisonous substances formed within the bacterial cell and released when the bacteria disintegrate. Endotoxins are natural compounds
found in organisms. Endotoxins do not multiply and are normally harmless, but if allowed
to enter the body (such as the bloodstream) they will produce toxic effects.
Bacteria can be sorted into two main groups through Gram stain: Gram-negative or
Gram-positive bacteria. After being stained, Gram-positive bacteria look purple under
the microscope, and Gram-negative bacteria look red. The distinction between these two
groups reflects fundamental and important differences in their cellular envelopes.
The Gram-positive bacteria have a stronger cell wall, comprised mainly of proteins and
carbohydrates, while the walls of the Gram-negative bacteria are comprised of fat, carbohydrates and proteins. Gram staining is useful for more than merely identifying microorganisms. It distinguishes microorganisms that differ from each other in several respects.
For example, certain disinfectants and antibiotics are more effective against Gram-positive bacteria than against Gram-negatives. Bacterial poisons (toxins) from Gram-positive
and Gram-negative bacteria have different characteristics. Gram-positive bacteria tend to
survive more readily than Gram-negative bacteria in a dry environment, whereas the latter
are often encountered in a moist environment.
Gram-negative intestinal bacteria can survive on surfaces such as instruments, tables
and doorknobs for a couple of hours, while Staphylococcus can survive for several
weeks.
Certain virus can survive for a very long time: Hepatitis-B virus can survive in dried blood
for several months.
There is no documented evidence that extensive disinfection of all surfaces in ward facilities or equivalent reduces hospital infections, but “spot-disinfection” and proper cleaning and sterilization of instruments and articles are of great importance
Effective mechanical and toxic armor
The bacterial cell wall has important functions in protecting the bacteria. The bacterial
cell wall has a complex chemical structure and is wrapped around the bacteria, defining
its size and shape: rods, cocci or spirillum. The bacterial cell not only determines the
bacteria cell shape – it contributes to the defense of the cell. Many antibiotics work by
interfering with different functions of the bacterial cell wall.
Gram-positive bacteria form a thick cell-wall barrier to the surrounding environment,
which allows the bacteria to survive in harsh environments.
Gram-negative bacteria have a thinner bacterial cell wall with a unique outer membrane.
The outer membrane is especially resistant to harmful chemicals, such as soap and disinfectants.
The outer leaflet of Gram-negative bacteria also contains a distinctive component – LPS
lipopolysaccharide – a potent endotoxin that can cause fever and shock when released
from the membrane. The endotoxin is released when the bacteria die and disintegrate.
The endotoxin is highly immunogenic and elicits a strong antibody response. Different
molecules in the endotoxin are highly varied and differ among bacteria, and even within
a specific species they are toxic and account for some of the virulence of certain Gramnegative bacteria.
Because of the variation, antibodies against one type of bacteria will not protect an individual from an infection with the very same bacteria if there are differences in the chemical
structure of the endotoxins.
In Escherichia coli, endotoxin causes severe infection, e.g. after ingestion of contaminated hamburger meat.
Basic hygiene - extremely important.
The sterilizing unit is probably the most important area in any healthcare setting. It is
estimated that 5% of all hospital patients develop an infection after being admitted.
When an infection is spread within a healthcare facility, it is almost certainly due to direct
contact with infected surfaces, skin, instruments, linen etc.
Healthcare centers involve tremendous flows of goods – instruments, trays, basins,
linens, bottles etc – some of which are soiled, some disinfected, some sterilized.
These flows must be strictly separated and the personnel must have secure procedures
and extensive knowledge in hygiene and infection control.
Goods that have been sterilized and then handled by someone who just handled soiled
goods are no longer sterile – and it makes no difference whether the goods are soiled
with living bacteria or the endotoxins of dead bacteria.
Staphylococci and tuberculoid bacteria can survive in the dry state for prolonged periods on contaminated surfaces and in dust. Other bacteria, e.g. those which cause gas
gangrene and tetanus, can form so-called spores. Under unfavorable conditions, these
bacteria envelop themselves in a capsule which is highly resistant to dehydration, acids
and particularly heat. They even tolerate boiling for several hours.
Another important distinguishing feature is dependence on oxygen. Certain bacteria require the presence of oxygen in order to grow (aerobic bacteria); others can grow with
or without oxygen (facultative anaerobic bacteria). A large group of bacteria in normal
human flora requires a completely oxygen-free environment (anaerobic bacteria). The
anaerobes are less likely than the other two types of bacteria to survive outside the host
organism
To survive and multiply, bacteria absorb substances from their surroundings. However,
bacteria cannot use large molecular nutrients such as starch and protein. These must be
broken down into less complex components to allow the bacteria to ingest them and use
them as nutrients.
The bacteria therefore form enzymes, which are excreted into the environment, e.g. when
they are in our body they break down the surrounding tissue. Thus the bacterial enzymes
contribute to the process of tissue destruction associated with infection. Certain bacteria also have the ability to produce and excrete toxins, which can, among other things,
reduce the body’s defense against infections. Furthermore, both bacterial enzymes and
toxins are important for the spread of disease-causing bacteria in the tissues.
Heat sterilization will kill the bacteria, but has little or no effect on the bacterial toxins. In
reality this means that, if not properly cleaned, sterilized instruments will be smeared with
biofilm comprising remnants of killed microorganisms and toxins. The instruments will
not cause any risk of an active infection, but the toxins can cause severe inflammatory
reactions.
Microorganisms require a suitable temperature in order to grow and multiply. The normal
human flora grow best at temperatures between +35°C and +37°C, i.e. normal body
temperature. This means that microorganisms which have optimum growth rates in other
temperature ranges cannot readily become established on human skin or in the gastrointestinal tract.
Facts and features - important blood-borne diseases caused by virus.
Hepatitis B
Hepatitis B is one of the major diseases of mankind and is a serious global public health problem. Hepatitis
means inflammation of the liver, and the most common cause is infection with one of 5 viruses, called
hepatitis A,B,C,D, and E. Hepatitis B is the most serious type of viral hepatitis and the only type causing
chronic hepatitis for which a vaccine is available.
Hepatitis B virus is not spread by contaminated food or water, and cannot be spread casually in the
workplace.
Hepatitis B virus is transmitted by contact with the blood or body fluids of an infected person in the same
way as human immunodeficiency virus (HIV), the virus that causes AIDS. However, HBV is 50 to 100 times
more infectious than HIV.
Worldwide, most infections occur from infected mother to child, from child-to-child contact in household
settings, and from reuse of unsterilized needles and syringes. In many developing countries, almost all
children become infected with the virus.
The majority of infections in many industrialized countries are acquired during young adulthood by sexual
activity, and by use of injected drugs. In addition, hepatitis B virus is the major infectious occupational
hazard of health workers, which is why healthcare workers should receive hepatitis B vaccine.
Hepatitis C
WHO estimates that about 180 million people, some 3% of the world’s population, are infected with hepatitis C virus (HCV). It is estimated that three to four million persons are newly infected each year, 70% of
whom will develop chronic hepatitis. Hepatitis C is responsible for 50–76% of all liver cancer cases, and two
thirds of all liver transplants in the developed world.
Hepatitis C virus infection runs with very few or no symptoms in 90% of cases. In 50–80% of adult cases,
the immune system is unable to eliminate the virus and the disease becomes chronic. Chronic hepatitis C
disease is the first cause of liver transplants in developed countries; about 20–50% of chronically infected
persons will eventually develop cirrhosis or cancer of the liver. It has been estimated that only about 50%
of HCV-infected persons are diagnosed in most developed countries and that two-thirds of them need to
undergo antiviral treatment.
Hepatitis C virus (HCV), very much like the human immunodeficiency virus (HIV), is characterized by the
continuous emergence of virus variants, thus making a moving target for vaccine design and for the host’s
immune system.
Water temperatures required in washer-disinfectors to kill/inactivate certain microorganisms:
HIV
(Strepto-, staphylococcus
Mycobacteria (M. Tuberculosis)
Hepatitis B-virus
(HBV)
Endospores
(Bacillus stearothermophilus)
+56°C
+63°C - +65°C
+72°C
>+90°C
+121°C
Note:
The temperature is not the only determining
factor. Other crucial functions for achieving
clean and disinfected devices are water flow,
water pressure, time interval at different temperatures, loading of washer-disinfectors, design of the washer-disinfection cycle as well
as choice of detergent.
Viruses – basic facts
Virus comprise a separate group within microbiology because they do not have an independent metabolism and cannot replicate independently. In contrast to bacteria, viruses
interfere with the metabolism of the host’s different cells and use these in order to replicate. Viruses can therefore attack only living cells.
Viruses are a very heterogeneous group and their composition is quite simple. The nucleoid of the virus particle (virion) consists of DNA (deoxyribonucleic acid) or RNA (ribonucleic acid). The virus uses the nucleic acid to control its replication within the host cell. The
nucleoid is surrounded by a protective protein shell, the so-called capsid. Certain viruses
also have a so-called envelope outside the capsid. The envelope consists of protein, fats
and carbohydrates. Viruses that lack an envelope are called naked viruses. On the outside of the capsid or envelope are projections with the ability to bind (affinity) to certain
so-called receptors on the surface of tissue cells to which the virus can attach.
Viral replication involves several steps:
Adsorption
Viruses bump into their host cell within the human body (or other living cells: animals,
herbs or other microorganisms) at random.
Penetration
Some virus enters the host cell completely or virtually intact. Other virus enters by fusing
into the cell.
Uncoating
Once the virus is inside the cell the envelop and/or the capsid are shed and the viral nucleic acids released.
Replication
During the replication phase the virus can either significantly interfere or alter the host
cells’ processes. After replication the virus is assembled and released from the cell through lysis or budding.
Major human diseases caused by virus
• Acquired immunodeficiency syndrome (AIDS)
• Adenovirus infection
• Chicken pox
• Common cold
• Coxsackievirus diseases
• Cytomegalovirus infection (CMV)
• Dengue fever
• Fever blisters
• Gastrointestinal disorders
• Herpes infections
• Hantavirus pulmonary syndrome
• Hemorrhagic fever
• Hepatitis
• Human immunodeficiency virus infection (HIV)
• Influenza
• Measles
• Mononucleosis
• Mumps
• Polio
• Rabies
• Rubella
• Severe acute respiratory syndrome (SARS)
• Smallpox
• Tick borne encephalitis (TBE)
• Warts
• West Nile encephalitis
• Yellow fever
Facts and features - important blood borne diseases caused by virus
(continuation).
Human Immunodeficiency Virus (HIV)
AIDS (acquired immunodeficiency syndrome) was first reported in the United States in 1981 and has since
become a major worldwide epidemic. AIDS is caused by HIV (human immunodeficiency virus). By killing or
damaging cells of the body’s immune system, HIV progressively destroys the body’s ability to fight infections and certain cancers.
The term AIDS applies to the most advanced stages of HIV infection. In people with AIDS, infections caused
by microorganisms that generally do not affect healthy people, are often severe and sometimes deadly. The
immune system is so weakened by the HIV that the body cannot fight off certain bacteria, viruses, fungi,
parasites, and other microbes.
HIV is spread by sexual contact with an infected person, by sharing needles and/or syringes (primarily in
connection with drug injection) with someone who is infected. Most infected persons you will not have any
symptoms when first becoming infected with HIV. Flu-like illness within a month or two after exposure to
the virus is common. These symptoms usually disappear within a week to a month and are often mistaken
for those of another viral infection. During this period, people are very infectious, and HIV is present in large
quantities in blood and genital fluids.
In the healthcare setting, workers have been infected with HIV after being stuck with needles containing HIV-infected blood or, less frequently, after infected blood gets into a worker’s open cut or a mucous
membrane (for example, the eyes or inside of the nose). HIV does not survive well in the environment. HIV
is found in varying concentrations or amounts in blood, semen, vaginal fluid, breast milk, saliva, and tears.
Drying of HIV-infected human blood or other body fluids reduces the theoretical risk of environmental transmission.
• Gloves should be worn during contact with blood or other body fluids that could possibly contain
visible blood, such as urine, feces, or vomit.
• Hands and other parts of the body should be washed immediately after contact with blood or other
body fluids, and surfaces soiled with blood should be disinfected appropriately.
• Needles and other sharp instruments should be used only when medically necessary and handled
according to recommendations for health-care settings. (Do not put caps back on needles by hand
or remove needles from syringes. Dispose of needles in puncture-proof containers.)
Accidental prick- and puncture wounds are the
major cause for healthcare personnel to acquire
blood-borne infections.
Calculated theoretical risks to aquire infections
after accidetal needle puncture:
Needle contaminated with:
Risk for infection:
Hepatitis B-virus
30%
Hepatitis C-virus
5%
HIV
< 1%
Gloves substantially reduce the amount of infectious
material that can be transferred from instruments.
If the puncture wound is caused by a hypodermic
needle, the amount of infectious material on the
needle is reduced by 46% when passing through
a glove. If the puncture wound is caused by a solid
suture needle, the amount of infectious material is
reduced by 86%.
Mast ST., et al. J Infect Dis 1993;168:1589-92
In the lytic viral infection, the virus goes through a cycle of replication, producing a large
number of new virus particles. The viruses are released by cell lysis which results in the
total destruction of the host cell. This type of cell destruction is typical for polio or influenza virus.
In other viral infections, the cells remain alive and continue to release new virus particles
at a slow rate. Hepatitis B is a typical example. Persistent infections are of great importance, as the infected person may be a symptom-free carrier, providing a continuing
source of infection.
A third alternative is latent infections, where the virus remains quiescent and the genetic
material of the virus may either exist in the host cell cytoplasm (as is the case with herpes
virus), or may be incorporated into the cell genome (retroviruses). Latent viruses require a
trigger (stimulus) to resume replication. Stress and UV-light exposure can start replication
of herpes simplex virus and stimulation of infected cells may provide signals that lead to
activation of HIV.
By interfering with normal cellular regulation, a number of viruses transform the host cell,
resulting in the development of a cancer cell.
Viruses can enter the human body through breaks in the skin or mucous membranes of
the gastrointestinal tract and are then disseminated; for example via the bloodstream, to
cells for which they have an affinity. After the virus has attached to the surface of the cell,
it invades the cell and takes over its metabolism, which results in the formation of more
viruses. Different species of virus attack different types of cell. For example, the Hepatitis
B virus (HBV) can attach only to hepatic cells: it invades and replicates within the hepatic
cell, which is damaged in the process and the disease hepatitis develops. Other types of
virus can attack only the mucous membrane cells lining the respiratory tract. These cells
are damaged and upper respiratory tract infections develop.
Naked viruses are usually smaller and tolerate changes in the environment better than
those with an envelope, which are often larger but more sensitive to changes in their
environment. For example, naked viruses tolerate low pH, the influence of protein-splitting enzymes and bile. They can therefore pass unaffected through the stomach into the
bowels. An example of a naked virus which tolerates this is the hepatitis A-virus (which
causes the most common epidemic form of hepatitis). Generally naked viruses also tolerate disinfectants, e.g. various phenol preparations, better than envelope viruses. Envelope viruses are more sensitive to common chemicals such as soap and detergents.
Even ether and chloroform can alter envelope viruses so that they can no longer attack
human cells. Human immunodeficiency virus (HIV) is an example of an envelope virus
which is quite readily inactivated by chemical disinfectants.
In general, viruses are heat-sensitive; several virus groups lose their ability to cause disease if they are heated to +60 °C for 30 minutes. One of the exceptions is the Hepatitis-B
virus which can tolerate temperatures between +90 °C and +100 °C for short periods.
Cross-infection control, hygiene, proper disinfection and sterilization are today’s
most important tasks in all healthcare systems.
Achieving an effective and efficient system for disinfection and sterilization takes
more than quality equipment. Profound knowledge of the essence of microbiology
as well as disinfection and sterilization practices are also important.
Facts and features: Prion disease - Creutzfeldt-Jakob disease.
Prion diseases in both humans and animals
There is evidence of 4 different human prion diseases (also named TSE, Transmissible spongiform encephalopathy), where the most common is Creutzfeldt-Jakob disease
(CJD).
In animals, 5 variants of prion diseases have been identified, the most well-known being
bovine spongiform encephalopathy (BSE, or “mad cow disease”).
Transmission of prions is usually by ingestion of contaminated tissues, but can occur
via medical procedures such as medical use of infected pituitary-derived hormones or
through surgical procedures including transplants of the cornea or membranes of the
brain.
Most cases not confirmed until after death
It is very difficult to diagnose patients with prion disease. Prions cannot be found in patient screening tests. There is no immune response, which means that the disease cannot
be found through antibody tests, unlike viral diseases such as hepatitis B, hepatitis C and
HIV. Prion disease can only be confirmed through microscopic analysis of brain biopsies
after the death of the patients.
Great care must be taken in disinfection and sterilization
Prions are extremely resistant. Small sub-populations can even survive steam sterilization. In worse-case scenarios (brain tissue bake-dried onto a surface), infectivity will be
largely but not completely removed.
The preferred policy for neurosurgical and ophthalmic instruments used in patients with
suspected CJD is quarantine, with later destruction if the diagnosis of CJD is confirmed.
To overcome the remarkable resistance of prions to disinfection and sterilization,
there are several treatments that significantly decrease levels of infectivity:
•
sodium hydroxide treatment (2 M for 1 hour)
•
sodium hypochlorite (20,000 ppm for 1 hour)
•
porous-load steam-sterilizing at 134° C (273° F) for 18 minutes or 6 consecutive sterilization cycles at the same temperature for 3 minutes per cycle.
Prions – basic facts
Prions are comprised solely of special protein molecules and in contrast to bacteria and
viruses do not have a genetic code. Prions are very resistant to inactivation, and can survive steam sterilization at 132-138º C. Prion-specific disinfection/sterilization is required
only in limited settings. Combining steam sterilization with a sodium hypochlorite treatment is extremely effective.
All proteins, including the prions, are formed in the tissue cells and those which are to
be used outside the cell are transported through the membrane of the host cell. Prions cause disease when normal protein molecules change shape and develop defective
forms. In contrast to the normal protein, the defective forms are not transported out of
the cell, but collect within the cell, which is eventually destroyed, releasing the defective,
disease-causing prions. These are carried to other nearby cells and cause the porous
transformation (spongiform degeneration) of the brain tissue (CNS) that is characteristic
of the disease. This is particularly so in the case of Creutzfeldt-Jakobs Disease (CJD)
and Bovine Spongiform Encephalopathy (BSE). The debut of the clinical phase of CJD is
usually in the age range 50-75 years.
Viroids –basic facts
Viroids are naked nucleic acid molecules consisting of RNA molecules not enclosed in a
protein shell. Most known viroids affect plants and there is only one recognized viroid-like
human agent – hepatitis D-virus. Hepatitis D uses the capsid of hepatitis B-virus, resulting
in a “two-for-the-price-of-one” infection
Mycoplasma – basic facts
Mycoplasma are small organisms. They are contained only by a cell membrane, with no
evidence of a cell wall.
Mycoplasma have adapted quite well to life without a cell wall and have a remarkable
ability to persist in harsh environments, including heat and chemicals.
New variant of prion disease
In the spring of 1996 a number of
Creutzfeldt-Jakob disease (CJD) cases
were reported in the United Kingdom, later
recognized as vCJD – new variant CJD.
Reports from the UK over the past 15
years have described over 130,000 “mad
cow disease” cases in domestic cattle.
Laboratory transmission studies show that
the infectious agent in vCDJ is likely to be
that of “mad cow disease” (BSE).
In December 2004, a total of 147 cases
were reported in the UK, in addition to
cases in France, Ireland, Italy, the USA,
Canada and Hong Kong.
Facts and features:
Major human diseases caused by mycobacteria
Airborne transmission of tubercle bacilli from infected persons
Lung tuberculosis infection is spread by coughing the germ, Mycobacterium tuberculosis, into the air. The
mode of transmission is exposure to tubercle bacilli in airborne droplets, produced by people with lung
tuberculosis during coughing, singing or sneezing, and inhaled by a vulnerable contact into the alveolae
of the lungs, where the tubercle bacteria initiate a new infection. In most forms of the disease, the bacillus
spreads slowly and widely in the lungs, causing the formation of hard nodules (tubercles) or large, cheese
like masses that break down the lung tissues and form cavities (empty holes) in the lungs. Direct invasion
through mucous membrane or breaks in the skin may occur but is rare.
Many infected - few diseased
Approximately 10% of those initially infected by the germ actually develop an active disease, half of them
during the first 2 years following infection. If untreated, about 65% of patients with so-called open pulmonary tuberculosis (sputum smear positive) will die within 5 years.
In the remaining 90%, a healthy immune system can contain the infection in a dormant state. Most of these
persons are unknown and untreated infected individuals.
Many years or decades later, these dormant infections may reactivate and cause active disease when the
immune system fails due to other diseases or simply ageing.
Tuberculosis affects more than the lungs
Infectious diseases caused by Mycobacterium tuberculosis may affect any organ or tissue: Lung tuberculosis (pulmonary TB) accounts for 70% of all cases, extrapulmonary tuberculosis, tuberculosis outside the
lungs, occurs less commonly, in 30%.
Patients with extrapulmonary tuberculosis are not likely to transmit the disease unless they also have tuberculosis of the lungs.
Increased risk for disease in patients with HIV/AIDS
The chance that anyone person will become ill with tuberculosis after infection is low, but in HIV-infected
persons, the chance of developing tuberculosis is accelerated by the failing immune system. Compared to
an individual who is not infected with HIV, an individual infected with HIV has a 10-fold greater risk of developing tuberculosis, and tuberculosis is responsible for over 30% of all HIV-related deaths.
Mycobacteria - a difficult bacteria
Mycobacterial infections are notoriously difficult to treat. Tubercle bacilli are dependent on oxygen (supplied
by air or from the bloodstream) to live and multiply. Since the bacilli are acid-resistant, they will survive the
natural acid barrier in the stomach. When swallowed, the tubercle bacilli will enter into other organs in the
body through the stomach and intestines, when coughing patients inevitably swallow their own sputum.
The tubercle bacilli are considered to have unusual resistance to conditions destructive to other bacteria,
but are also susceptible to specific physical and chemical agents. This is due to their cell wall, which is
unique to the family. They are naturally resistant to a large number of antibiotics. Because of this unique
cell wall, they can survive long exposure to acids, alkalis, detergents, oxidative bursts, factors within the
immune system and antibiotics (which naturally leads to antibiotic resistance).
The tubercle bacilli is relatively resistant to dry heat, but is killed by boiling for 2 minutes. It is not killed by
freezing and is highly resistant to desiccation. The tubercle bacilli has been shown to survive up to 5 months
on surfaces and items, but the bacillus is sensitive to sunlight – ultraviolet radiation.
Tubercle bacilli can survive disinfectants if embedded in biological material – which stresses the importance
of thorough cleaning of instruments prior to disinfection.
Ethyl and isopropyl alcohols in high concentrations are generally accepted to be excellent mycobactericidal
agents. A distinctive disadvantage of alcohols is their relative inactivity in the presence of organic material.
Alcohols cause coagulation of proteins, causing so-called “trapping effects”. Consequently, cleaning with
detergents must precede alcohol disinfection – or tensides should be included in the disinfectant agent
Steam sterilization is preferable to dry heat sterilization since the tubercle bacillus is relatively
resistant to dry heat and highly resistant to desiccation. In worse case, if embedded in biological
material, there is a risk that the tubercle bacilli might survive dry heat sterilization.
Mycobacteria – basic facts
Mycobacteria comprise a considerable number of species that are widespread in nature.
Most live as saprophytes (i.e. living on decaying organic matter), but a smaller number are
human pathogens, the most important two being M tuberculosis and M leprae.
The mycobacteria have cell walls rich in lipid (fat) content, which makes the organisms
acid-resistant. Mycobacteria are thermosensitive, i.e. they can be destroyed by heating.
The lipid in the cell wall consists of waxes. The robust waxy cell membrane of mycobacteria
makes them extremely resistant to disinfectants, strong acids and also white blood cells.
The disadvantage for mycobacteria is their very slow growth rate. The rate of nutrient
uptake is 100 to 1000 times lower than for the most common gram-negative bacteria. In
general, the slow growth rate of the mycobacterium means that it requires 2 to 8 weeks
or longer for detection than ordinary bacteria.
Mycobacteria are also sensitive to sunlight, but tolerate cold and dehydration well. At least
25 species of mycobacteria are associated with human disease, and tend to produce
gradually developing diseases.
So-called atypical or silent mycobacteria, causing other mycobacterial infections than
tuberculoid bacteria, have attracted increasing interest in recent years, as the number
of diagnosed cases has increased. The explanation is to be found partly in improved
diagnostic techniques but also in an increasing number of patients with immuno-deficient
conditions. It is common to find mycobacterial infections in immuno-compromised patients,
particularly those with acquired immunodeficiency syndrome (AIDS). The disease may be
confined to a cooler, more superficial part of the body, or it may invade the internal organs
and cause disseminated disease.
The slow growth rate of mycobacteria is a major problem, as patients often show no
symptoms until the disease is well established and has caused severe damage.
Because of the slow growth rate, antimicrobial medication requires long treatment
periods (several months) with the risk that the patients will discontinue treatment once
they are symptom-free. This is also the major factor behind the development of antibiotic
resistance in mycobacterias.
Tuberculosis (TB) is a serious public health, social and economic problem. One third (1.9
billion)of the world’s 6 billion people have been infected and must be regarded as potential carriers of the bacilli.
Tuberculosis is estimated to cause 8 million new cases world wide each year. There are
more than 1.9 million deaths due to tuberculosis each year. Tuberculosis kills more youth
and adults than any other infectious disease.
The disease burden is heaviest in developing countries, where 95% of the cases occur.
Even in developed countries, tuberculosis is re-emerging as a public health concern.
Mycobacteria other than M. tuberculosis may produce disease in humans. Of the identified species of mycobacteria other than tuberculosis (MOTT) only about 15 are recognized
to be able to cause disease in people. The incidence of atypical mycobacterial infections
is rare, but it is increasing as the AIDS population grows.
Populations at risk include individuals with pre-existing lung disease and immuno-compromised persons. These types of infections are a major problem in HIV-infected persons.
Facts and features:
Major human diseases caused by mycobacteria - continued
Air control - the most important way to reduce the risk for tuberculosis in the medical
environment
The risk of acquiring tuberculosis in a medical environment is almost exclusively a function of the concentration
of infectious particles in the air. In areas occupied by known or suspected producers (patients with active
lung tuberculosis, producing airborne droplets enclosing tubercle bacilli, during coughing or sneezing) of
infectious airborne particles, air control is necessary. This is accomplished by ventilation, high-efficiency air
filtration and the use of ultraviolet irradiation. Good ventilation is of obvious importance in diluting airborne
particles. Six air turnovers per hour reduce the concentration of infectious particles to 1% of the initial
level.
Ultraviolet light has long been known to be effective in destroying infectious airborne particles. The
disadvantages of its use include eye irritation and extensive maintenance requirements. Tubes must be
scrupulously cleaned and emission levels (quality of ultraviolet irradiation) frequently monitored.
Medical devices can be a risk for patient-to-patient spread of tuberculosis
There are reports on cross-infection from medical devices. The risk of patient-to-patient spread of
mycobacterial infection through inadequately disinfected instruments is centered on the use of bronchoscopy,
intubation and mechanical ventilation of infected patients.
Mycobacteria are generally more resistant to chemical disinfection than other bacteria. Any disinfectants
used should have a documented mycobactericidal effect.
The importance of thorough cleaning of instruments and articles prior to disinfection must be stressed.
As described previously, mycobacteria can survive for a very long time if embedded in biological material.
There are reports that M tuberculosis can survive in tuberculosis tissue stored in 10% formalin for as long
as one year.
Water - the importance of microbiological quality
Hard water results in a build-up of lime scale on the internal pipework of washer-disinfectors as well as
steam sterilizers. Together with poor microbiological quality of water, this may result in microorganisms being
entrapped within lime scale deposits. Disease-causing microorganisms can be transferred to instruments
directly from the free content in water or from microorganisms released from the lime deposit. Tap water
may contain microbes, including Pseudomonas spp and Mycobacterium spp, and there are many reports
of procedure-acquired infection with these microorganisms.
There are reasons for the use of pre-sterilized water. Misdiagnosis of tuberculosis has been reported due to
contamination of the instruments with environmental mycobacteria from the rinse water, which subsequently
contaminated bronchial washings sent for culture. Sterile water is recommended for the final rinse of all
types of endoscopes to be used for invasive procedures.
The eternal importance of hand hygiene...
It is important to keep in mind that the transfer of microorganisms to instruments after the disinfection and
sterilization process is largely via the hands of the personnel.
Proper hand disinfection is crucial to minimize the impact of transferal of microorganisms during the
reprocessing of instruments and articles. There are findings showing that harmful microbes can survive
up to 38 weeks on sterile wrapping material, if contaminated by environmental microbial flora during the
reprocessing cycle.
Fungi – basic facts
Most fungal infections are not contagious but are acquired through exposure. They are
extremely successful organisms, as evidenced by their ubiquity in nature. They are an
important component in the energy cycle, where they function as decomposers.
Fungi are thus valuable as saprophytes in nature. Of the estimated 250 000 species,
fewer than 100 are known to be primary pathogens in humans. Fungi can be grouped as
either yeasts or moulds.
Yeasts are by far the most common fungi in humans. Yeasts may infect patients debilitated in some way, e.g. by hormone imbalance or by administration of immuno-suppressive agents such as corticosteroids, anticancer drugs, the newer anti-AIDS-drugs, or the
overuse of broad-spectrum antibiotics. Patients who undergo transplant surgery and/or
immuno-suppressive drug medications often acquire yeast infections. Diseases such as
AIDS and others that cause a diminution or depletion of the immunological system are
also predisposing factors for yeast infections.
Endocarditis caused by yeast has been associated with the use of non-sterile equipment
by drug addicts.
Fungemia may occur when indwelling catheters are not changed or removed at frequent
intervals. General fungal infections are severe and life-threatening diseases.
An important fact is that most individuals are carriers of fungal spores; on the surface of
the skin, in clothes and in the oral cavity etc. Under normal conditions the fungal spores
never get the chance to mature – the fungal spores are kept in check by the immune
system. However, when there is a local or general immuno-deficiency, this will predispose
for establishment of fungal infections.
One can say that fungal infections are not contagious; it is the body’s own weakened
defense functions that make fungal infection possible.
Patients with fungal infections should always be treated under close surveillance. It is also
of greatest importance to find the primary cause of fungal infections, which will always be
a general or local immuno-deficiency !
Microbial communication
Biofilm is a microbial community characterized by cells that are attached to a surface or to
each other, embedded in a matrix that they have produced. Biofilm formation is controlled
by a communication mechanism between bacteria. In other words, this means that the
bacterial cells are “talking” to each other by using specific chemical substances.
Through these chemical radio transmissions, the bacteria within the biofilm will “know”
how to build the biofilm and how many and which bacteria should inhabit the biofilm. If
the biofilm becomes too thick, there will be no oxygen and other nutrients for the bacteria
in the deepest layer. If the biofilm is too dense there will be no possibilities to transport
necessary liquids to and from individual bacteria. In the biofilm, bacteria require an “infrastructure” similar to humans building a new living area: there must be space, roads for
transport, fresh water systems, sewage systems, defense, communication systems etc.
In this sense, biofilms are a very fascinating and sophisticated microsociety.
The biofilm constitutes a highly effective defense barrier. Bacterial cells within the biofilm
are protected from disinfectants, host defenses and antibiotics.
When reprocessing instruments and articles, it is crucial that all
biofilms are effectively removed during the cleaning process. If not,
the bacteria will be protected by the biofilm and the subsequent
disinfection and sterilization will not be effective!
Bacteria that attach to surfaces aggregate to form biofilms. Formation of biofilms and their
resistance to antimicrobial agents are at the root of many persistent and chronic bacterial
infections.
In the example above: A certain concentration of disinfectant (in this case, sodium
hypochlorite) is needed for lethal effect on free floating bacteria. If the very same bacteria
exist within an established biofilm, the concentration of the disinfectant in question has to be
increased at least 3,000 times to have the same lethal effect.
Biofilms and D-values – crucial factors
Biofilm a perfect protection
Microorganisms free-floating in liquid (water) are referred to as planktonic microorganisms. Most research and testing of the effects of different disinfection methods are carried out on planktonic microorganisms, but this does not give the full picture. In nature,
several microbial species form a complex biofilm which, among other functions, serves
as a protection for the microorganisms.
Moisture and microorganisms essential for biofilms
Biofilms are very common and defined as a mass of microorganisms attached to a surface exposed to moisture. Where there is moisture and microorganisms, there will also
be biofilm. This includes surfaces associated with natural water environments as well
as domestic and industrial water systems. Biofilms also form on biomedical materials
implanted in or associated with the human body, including catheters, sutures, wound
drainage tubes, endotracheal tubes, mechanical heart valves and intrauterine contraceptive devices.
Not fully understood until 1978
Biofilms were first described by Antonie van Leeuwenhoek (1632–1723), but the theory
describing the biofilm process was not developed until 1978. Biofilms occur universally
and microorganisms growing in a biofilm are highly resistant to antimicrobial agents by
one or more mechanisms. Biofilm formation represents a protected mode of growth that
allows cells to survive in hostile environments.
Dental plaque – a well known biofilm
Dental plaque on tooth surfaces in the oral cavity is a good example of biofilm formation. The formation of dental plaque requires that certain bacterial species, notably
Streptococcus mutans, stick to the tooth surface first. Bacteria from other species such
as actinomycetes stick to the pioneers, then other microorganisms stick to the actinomycetes leading to a complex biofilm with a large variety of microbial species.
Most equipment-associated infections are due to inadequate cleaning and disinfection. If the
goods are not ultra-clean, sterilization will not be effective.
Personnel working with disinfection and sterilization have a great responsibility to scrutinize all
processed items. Critical results of often costly healthcare procedures depend on their working meticulously and with great care.
Confusion: bacterial biofilm vs bioburden
Biofilms adhere to a foreign body or a mucosal surface with impaired host defense, and
many hospital-acquired infections involve bacterial biofilms.
Bacterial biofilms are often confused with the bioburden of medical devices. The bioburden is most often defined as the microbiological load, e.g. the number of contaminating
organisms in the product/item prior to cleaning, disinfection and sterilization. However,
bioburden can also be biological materials such as blood, mucos, fluids, feces, etc, and
when present on items to be processed for reuse
Cleaning, always the most important step
The most effective stage of any decontamination procedure is thorough physical cleaning
and this should accompany or precede all disinfection procedures.
An item heavily loaded with biological material will be more difficult to sterilize than one
lightly contaminated. Medical devices requiring sterilization or disinfection must therefore
be thoroughly cleaned to reduce organic material or bioburden.
Cleaning involves the removal of organic substances and other residues from a surface
or item. Cleaning in itself does not cover any microbial killing action and should therefore
not be confused with decontamination and disinfection.
Cleaning and disinfection of instruments should be carried out as soon as possible after
use. Dried biological material is much more difficult to remove than fresh deposits. Blood,
with its content of iron, acid, sodium chloride and several electrolytes, is corrosive. The
drying of blood means that the amount of water decreases, and that the concentration
of all corrosive substances will increase. There will be the same content of electrolytes in
less volume of water.
Remaining biological material on the instruments can also occlude microorganisms and
protect them from penetration of the disinfecting/sterilizing agent. Pre-soaks of surgical
instruments directly after use at the operating room significantly facilitate the subsequent
cleaning process and thereby also improve the effect of the disinfecting and sterilizing
process.
IInstruments consisting of several parts should always be dismantled as much as possible to clean all accessible surfaces in order to remove all biological deposits.
Disinfection with aldehydes before cleaning of instruments must be avoided because
protein coagulation as well as fixation of bioburden and bacterial biofilms will occur. This
is especially important for instruments with long and narrow hollow parts (lumina). Hollow
instruments are difficult to inspect in order to find remaining biological material.
The most effective stage of any decontamination procedure is thorough
physical cleaning. Physical cleaning means the use of mechanical forces
to remove residual bioburden and biofilm from all surfaces of the instruments/articles. This must be done without harming and destroying the surface of the items.
Physical cleaning can be achieved by: scrubbing of instruments with soft
brushes and proper detergents, ultrasonic cleaning and in automated washer-disinfectors. Automated processors offer the safest, most reliable option.
Microbial corrosion and surface destruction
As the different microorganisms develop, molecular or proton exchanges occur which
can cause microbial corrosion. The corrosion process can be initiated by the formation of
either differential concentration cells or by local electrochemical corrosion cells within the
biofilm in which the concentration of protons and other cat ions is formed.
In the oral cavity the formation of protons and cat ions will eventually lead to the destruction of tooth structure, cavities or tooth decay.
It is important to remember that biofilm on instruments and medical devices works in the
very same way, which will lead to bacterial corrosion and corrosion pits on the surface
of the article. Once corroded the surface of the instrument or medical device will not be
smooth and therefore with continuous bacterial/biofilm caused corrosion it will be easier
for bacteria and other bioburden to attach to the surface. An uneven surface full of corrosion pits will also become more and more difficult to clean.
Biofilm on medical implants
Medical implants that can be compromised by biofilm-associated infections include:
central venous catheters, heart valves, ventricular assist devices, coronary stents, neurosurgical ventricular shunts, implantable neurological stimulators, arthro-prostheses,
fracture-fixation devices, inflatable penile implants, breast implants, cochlear implants,
intraocular lenses and dental implants, to mention some examples. Again, where there
is moisture and microorganisms, there will also be biofilm. In healthcare situations, the
moisture comes from body fluids and the microorganisms either naturally occurring or
introduced during healthcare procedures. Microorganisms that form the biofilm are often
due to cross-contamination, through improper aseptic techniques or inadequately processed instruments.
More difficult to treat infections due to biofilms
The bacterial cells within the biofilm are protected from disinfectants, host defenses and
antibiotics. Clinical experience has shown that they must be removed physically before
the infection can be effectively treated.
Treatments and infection control strategies that inhibit the formation of biofilm are important in inhibiting infections. Instruments and medical implants have become the focus
of device-related and biofilm-related infections. These infections are difficult to treat because bacteria that cause these infections live in well-developed biofilms.
D-value – life expectancy of bacterial endospores
To determine the effective heat treatment required to kill a specific microorganism, it is necessary to quantitatively determine the death rate. One of the best methods is by determining the decimal reduction times or
D-value. The D-value is a measure of the heat resistance of a microorganism. It is the time in minutes at a
given temperature required to destroy the microorganism by a factor of 10, for example from 10,000 (104)
living bacteria down to 1,000 (103). Thus 9,000 bacteria (90%) have been killed.
In the diagram above, the D-values (d1, d2, d3) represent the sterilization times (holding times) needed to
reduce the number of living microorganisms to one-tenth (1/10) under preset conditions. The curves representing the loads of microorganisms A and B have the same D-values, but the number of microorganisms
in load A is much lower at baseline 101 (less “bioburden”). A will reach the theoretical and critical level
SAL=10-6 at an earlier point than B, which represents a heavier load at baseline 106. SAL=10-6 represents
the theoretical sterility assurance level required for an article to be labeled STERILE. (In accordance with
ISO 14937 and EN 556:1994).
In this diagram, curve B could very well represent an uncleaned instrument and curve A the very same
instrument after proper cleaning and removal of all biofilms and bioburden. The safety margin of the sterilization process will be much larger in the case represented by curve A.
The load of microorganisms represented by curve C has much higher heat resistance (higher D-value) and
will require a much longer sterilization time than both A and B to fulfill the demands for sterile articles.
The reason for using D-values and a logarithmic scale is that even within the same bacterial population
there are individuals with different resistance. In the beginning of the sterilization process it is easy to kill a
large number of microorganisms in a short period of time, but in the end only the most resistant microorganisms will remain alive – and they will be much more difficult to inactivate. This is also related to the
nature of biofilms and bioburden; the more embedded the bacteria, the more difficult the sterilization will be.
More about process challenge devices will be described in following chapters covering:
Disinfection; Sterilization; and Validation, Process Challenge Devices and Quality Indicators.
.
Bacterial resistance to sterilization depends on many factors
During both disinfection as well as sterilization, the result of the process will depend on
the number of microorganisms present on the article before the disinfection or sterilization
process begins. It will also depend on their resistance to the disinfection or sterilization
process. The quality of biofilm is another important factor.
Forming of bacterial endospores – coordinated behavior
Sporulation, the transformation of bacteria into bacterial endospores, is not the activity of
a single bacterial cell. In biofilms, sporulation depends on the ability of bacteria to communicate and coordinate behavior, and in that sense sporforming bacteria form communities that behave as multicellular organisms.
This means that when sporulation occurs in an environment that is hostile to the bacteria,
the coordinated behavior of the bacteria will cause almost the whole bacterial community
to form a large number of highly resistant endospores. Again, the bacterial biofilm
plays a very important role in giving the bacteria the possibilities to work together like a whole community.
Bacterial endospores resistant to almost everything
Formation of spores is not a normal part of the bacterial life cycle but a defense mechanism used to survive. Spores are resistant to temperature, desiccation, organic solvents,
ultraviolet light, and most other agents. Many spores can withstand boiling in water, and
spores in soil can persist for decades, perhaps centuries. Because of the very high resistance, bacterial endospores can be used as a process challenge device for sterilizers
– if the sterilizer is capable of killing bacterial endospores, a good assumption is that the
sterilizers also will kill everything else. However, using bacterial endospores as a process
challenge device for sterilizers will not tell the whole story. A major question must be how
the bacterial endospores will be affected if embedded in a biofilm matrix. The most critical part of all sterilization will be proper cleaning of instruments before sterilization. If not
ultraclean, sterilization will not be
effective. It is more difficult to sterilize a product heavily loaded with spores than one lightly
loaded.
Not only the instruments...
In hospital environments, a well-known problem is spore-forming bacteria of the genus Clostridium.
Clostridium difficile can be part of the normal intestinal flora. Disease occurs when the normal intestinal flora is altered, allowing Clostridium difficile to flourish in the intestinal tract and produce a toxin
that causes a watery diarrhea. Spores can survive up to 70 days in this environment. Strict adherence
to hand-washing procedures and the proper handling of contaminated wastes as well as safe methods for disinfection/sterilization are effective in preventing the spread of the disease.
The formation of spores is also a serious concern for the food industry, because spores in incompletely cooked (sterilized) foods can germinate in the container. Potent toxins are produced by many
members of the genus Clostridium, including Clostridium botulinum, Clostridium tetani, and Clostridium perfringens, which thrive under the anaerobic conditions found in most canned foods.
In all types of food preparation, the growth of spore-forming as well as toxin-producing microorganisms must be completely prevented. Food and food preparation areas are prone to biofilm formations. In hospital premises, many different kinds of microorganisms are to be found, as well as
immuno-compromised patients.
Understanding the importance of preventing biofilm formation is crucial at all levels and
in all types of healthcare settings.
Hepatitis B,
- the burden of disease
Hepatitis B virus (HBV) infection is a
serious global health problem, with
2 billion people infected worldwide,
and 350 million suffering from chronic
HBV infection. The 10th leading cause
of death worldwide, HBV infections
result in 500 000 to 1.2 million
deaths per year caused by chronic
hepatitis, cirrhosis, and hepatocellular
carcinoma.
In health care settings transfusion of
blood or blood products, hemodialysis,
acupuncture and needlestick or
other sharp injuries can result in HBV
transmission.
In dried blood on instruments,
hepatitis B virus can survive for
several months.
Hepatitis B -- most cases unidentified
A small proportion of acute hepatitis B (HBV) infection may be clinically recognized; less than 10% of children and 30%-50% of adults with acute hepatitis B infection show icteric disease (jaundice). However icteric
disease is a symptom seen in many other diseases and conditions when the liver is affected.
Chronic hepatitis B infection is found in 0.1% - 20% of adults, depending on the world region. Those
whose condition will become chronic include about 90% of those infected at birth, 20%-50% of children
infected from 1 to 5 years and 1%-10% of older children and adults. An estimated 15%-25% of persons
with chronic hepatitis B infection will die prematurely of either cirrhosis or hepatitis B-associated liver cancer
(hepatocellular carcinoma). Hepatitis B probably causes up to 80% of all cases of hepatocellular carcinoma
worldwide. Hepatitis B is the second most common factor behind cancer diseases, the most common
being tobacco-related cancers. Patients who develop chronic hepatitis B infection most commonly belong
to the group ”symptom-free” during the acute stage of the hepatitis B infection.
The above example with hepatitis B clearly demonstrates the importance of proper infection
control: if an instrument is not carefully cleaned there might be remnants of hepatitis B-infected
blood from an unidentified carrier (they are most common). The next patient will get a symptomfree infection and the disease will not be discovered until decades later when this person has
developed a hepatitis B-associated hepatocellular carcinoma. At that time it will be impossible
to trace the infection to the lack of prudent cleaning of a single instrument in some healthcare
setting.
Every year the consequences and costs to the global society from the burden of hepatitis Bassociated healthcare and loss of life ends up in astronomical figures. With current knowledge
about infection control, one must ask how many of these cases and how much healthcare resources and loss of human resources are due to inaccurate health care procedures, poor quality
and negligence.
The risk of transmission of infection associated with punctures and needlestick is strongly associated with
blood-borne infection, particularly hepatitis. It is therefore important that blood and body fluids from all patients are handled with due caution.
The most important and simplest recommendation for adequate infection protection is always to work
calmly and methodically and always follow the same routines. Most incidents and mistakes occur under
conditions of stress, shortage of time or uncertainty.
Infection – inflammation, what is the difference?
Infection is a condition in which an infectious agent has invaded the body and multiplied.
Inflammation is the body’s response to infection. Inflammatory reactions also protect the
body from foreign substances and start healing processes when something has caused
damage.
Infection is characterized by something ”non-human” that is growing, increasing in number, producing toxic substances and using the systems of the human body for its own
purposes. The infectious agent – the microorganisms – can be bacteria, mycoplasma,
fungi, protozoa or viruses.
Infections usually take time
A common misconception is that an individual who is infected with a pathogenic microorganism rapidly develops symptoms and becomes acutely ill after an incubation period
of 24 to 48 hours.
Infection with or without symptom
If however, the infection is transmitted it can lead either to clinical disease (with symptoms)
or subclinical disease (asymptomatic) or the recipient can be colonized by the infectious
agent without developing the disease. If the recipient develops an infection, (clinical or
subclinical) the infection can either heal, become chronic (e.g. HIV) or latent, with the potential to reactivate (e.g. herpes simplex).
Most incidents of spread of infection do not lead to an infection, but the infectious agent
is dealt with by the immune system, is ”mechanically” removed or is integrated into the
normal flora over a longer or shorter period of time. In those cases where the recipient
does acquire an infection, the process is usually quite asymptomatic. Only certain infectious agents are so virulent (aggressive) that they primarily cause disease.
It is important to realize that many infections and infectious agents can be transmitted without a diagnosis or awareness of the presence of an infectious agent. In acute infections
the infectivity is often greatest before characteristic symptoms develop. Having a chronic
infection or being a carrier of antibiotic resistant bacteria is often symptom-free.
Herpes virus is a typical example of how viral infections behave.
Labial herpes is a common viral disease caused by HSV 1 - Herpes Simplex Virus 1
Herpes simplex is a viral infection characterized by localized blisters, latency and a
tendency to reoccur with irregular intervals. Primary (acute) infection occurs early in
childhood. Worldwide, 50-90% of adults have antibodies against the virus, meaning that
the virus has been dealt with by the immune system.
Some of these individuals will be life-long carriers of the virus (the herpes virus has
”reprogrammed” some of there cells to be virus producers). Life-long chronic carriers
can be with or without recurring blisters, and are potential sources for spreading the
infection to others.
Facts and features:
How do decontamination and disinfection affect inflammation and
infection?
Decontamination to remove dirt, soil and impurities
After usage, instruments are always contaminated. Contamination simply means that
the items are soiled. Impurities can be anything from blood, body fluids, remnants of
tissue but this does not necessarily mean that there will be any microorganisms present.
Contamination can also comprise inorganic material such as lubricants, fibers, chemicals
etc. There is an important distinction between decontamination and disinfection:
Decontamination refers to the removal of all types of soil and impurities on instruments
and articles. Decontamination will not include the microbial killing action of a disinfection
process. The cleaning of articles with soap and water is one type of decontamination.
Decontamination is a term used to describe a process capable of rendering an item
(medical device, instrument, surface) safe to handle. Decontamination does not necessarily
mean that the article in question is safe for patient use.
Disinfection to deactivate microorganisms
Colonization means that something is living and multiplying in an area, on an instrument
or medical device. In the case of microorganisms, they have created a microbial society
(see also chapter on biofilms). Disinfection is necessary to stop continuous microbial
growth. Disinfection is defined as a process to deactivate all recognized microorganisms
but not all microbial forms (bacterial endospores) on inanimate objects.
More simply, this can be described as disinfection procedures lacking the sporicidal
power of sterilization. The margin of safety is much larger in a sterilization procedure
since disinfection does not ensure the same overkill as sterilization.
Disinfection and sterilization processes are intended to destroy / deactivate (kill)
microorganisms but will not necessarily remove the impurities (the bioburden and/or
inorganic burden) on items!
Do not confuse decontamination and disinfection !
When reprocessing instruments and other medical devices, it is crucial to understand that
decontamination and disinfection are not the same thing. However, reprocessing requires
both steps and in the correct order. Living microbes will eventually cause infection that
will lead to inflammatory reactions. Dead / deactivated microbes and other impurities will
directly cause inflammatory reactions.
Contaminated or colonized – not the same as infected and diseased
Infected people can often be carriers of pathogenic microorganisms without this resulting
in them having any disease themselves. However, microorganisms can be transmitted
from the ”healthy” carrier to other people who then develop disease. It is important to
recognize the differences between contaminated, colonized, infected and diseased.
Contaminate – adding substances that are dangerous to someone or something. To be
contaminated with a microorganisms means that the microbe is temporarily present in the
host but has not established and does not multiply.
Colonize – the microorganism in question has become established for a shorter or longer
period of time and created its own niche where the microbe can live, thrive and multiply.
Colonization means that the microorganism is there without causing harm to the host.
Infected – the microorganism has taken over, become established, lives, thrives and
multiplies in a minor or major area of the host and interferes with the host’s natural ecology
for a longer or shorter period of time. Infection can be with or without symptoms.
Diseased – the infection is now interfering so much with the host ecology that
symptoms of disease will occur.
Virulence and pathogenicity
The virulence of a microorganism and its pathogenicity (its potential to cause disease)
and the current resistance of the individual (immune defense) determine the development
of the infectious disease. The more virulent it is, the fewer microorganisms are needed to
cause infection. The more pathogenic, the more severe disease will be caused by each
individual microorganism.
Disease-causing toxins
Bacterial infections cause local or general symptoms from toxins formed by the
microorganisms. Toxins can take the form of endo- or exotoxins. The endotoxins are
often remnants of microorganisms, parts of the cell walls etc, or poisonous substances
formed within the bacterial cell and released when the bacteria disintegrate. Exotoxins
are poisons excreted by living bacteria, mainly the Gram-positive type: exotoxins are the
most powerful poisons known e.g. the exotoxin of the tetanus bacillus.
The path of infection – rapid or slow ?
Bacterial infections, e.g. food poisoning and certain streptococcal infections, can run a very
rapid course. They can also have a very indolent pattern, with long periods of mild fever
as the only symptom, e.g. mycoplasma pneumonia, and certain types of endocarditis.
Bacteria can also colonize different parts of the body for long periods without causing
symptoms. When the individual’s immune defense is weakened for some reason, the
infection can enter an acute phase.
Virus dependent on living host cells
In the case of viral infections, the virus uses the genetic material of the target cells of the
host. Viruses always have specific target cells, e.g. the hepatitis virus attacks cells of
the liver. The genetic material of the virus (DNA or RNA) is incorporated into the genetic
material (DNA) of the target cell. Viruses can only multiply in living cells. Energy and material
for replication are obtained from the host/target cell.
The target cell is infected and ”reprogrammed” to produce new virus particles.
Paths of infection of importance in health care settings
Direct contact transmission. The source of infection is physical contact with the susceptible
individual/ tissue. It is believed that this is the means by which sexual diseases are
transmitted. Another example is seen in healthcare personnel who are carriers of the
disease and have sores on their hands. The infectious agent is transmitted from the sores
to the patient.
Inoculation transmission. Is a particular form of contact transmission, in which infected
blood on soiled, sharp instruments penetrates the tissue beneath the skin or mucous
membrane in the form of a prick or puncture wound.
Indirect contact transmission. In indirect contact transmission there are various intermediate
stages. In principle, indirect contact transmission in healthcare settings can occur in two
ways: the first is via the skin, nails and work clothes of the staff. The second is primarily by
use of instruments which have been poorly cleaned or not cleaned at all. The instruments
become contaminated with microorganisms during clinical use and the microorganisms
have the ability to survive on the surfaces of instruments for a relatively long time.
Droplet transmission. Coughing, sneezing, vomiting etc send a shower of large heavy
droplets which quickly descend from the air. The infectious agent does not reach further
than an ”arm’s length” from the face. The droplets can infect through direct contact with
the recipient (splashing the membranes of the eyes, nose or mouth) or via the hands
(direct contact transmission). Example: respiratory tract infections.
Airborne transmission. The droplets can dry out to form so-called droplet nuclei which are
spread in the air. Examples: varicella, influenza, plague.
Faecal transmission. Infectious agents which are excreted with the bowel contents and
in some way reach the mouth (faecal-oral transmission) via direct or indirect contact
transmission, or alternatively through water or food. Examples: hepatitis A., salmonella,
typhoid.
Vector-borne transmission, Insect-borne transmission. Certain infectious agents are
transmitted by insects. E,g, malaria, West Nile virus. (Such infections are not usually a
major problem in health care settings).
In some countries, the proportion
of injections given with syringes or
needles reused without sterilization
is as high as 70%.
This exposes millions of people to
infections.
Each year, unsafe injections cause
1.3 million deaths, primarily due to
transmission of blood-borne pathogens such as hepatitis B virus, hepatitis C virus and HIV.
Similarity between virus in nature and computer virus
The reason why computer software programs designed to infiltrate and damage computers, networks and servers are called “virus” is the similarity with biological virus. Both
types of “virus” have the capability to reprogram “the host” for their own purposes.
Intact skin and mucosa – the most important part of our immune system
The human body has natural and important protective barriers against, among other
things, microorganisms: skin, mucous membranes and - in the mouth - the enamel and
dentine layers of the teeth. When the barrier is broached and the immune defense fails,
this creates conditions for establishment of microorganisms in the tissues, which in turn
can lead to infection.
Superficial structures – the border defense
The function of the protective barriers of the body is to protect us from microorganisms
and various types of damage. In the skin, just beneath the layer of epithelium, is a very
fine, extensive capillary bed. There are also a great variety of defense cells and sensory
nerve endings. A shallow cut bleeds relatively profusely compared with a deeper cut into
the underlying tissues which are not as richly vascularized. A shallow cut is also more
painful than a deeper cut – a clear example of how the protective barrier functions. This is
also the reason why an aseptic approach is so important during deep invasive treatment/
surgery involving sterile tissues distant from the body’s protective barrier, a field which
is relatively poorly vascularized and therefore has less effective defense against invasion
in the form of microorganisms than intervention closer to the surface. The skin surface
contains antimicrobial substances, such as salt in high concentrations, certain peptides
and fatty acids. Lactic acid and fatty acids are present in sweat and sebaceous secretion
attributing to a lower pH (pH 5.5) on the skin, which has a direct inhibitory effect on many
bacteria.
Friendly bacteria – an important co-worker in our immune system
The normal bacterial flora of the body suppress the growth of many potential pathogens:
first by virtue of physical advantage of previous occupancy, second by competing for essential nutrients and third by producing inhibitory substances.
The importance of proper care of the skin is obvious. Wounds, abrasions or burns are
common sites of infection. Even a small break in the skin can be a portal of entry if virulent
microorganisms are present at the site.
Be careful with the skin !
Over-enthusiastic skin hygiene, the use of abrasive techniques, antimicrobial soaps,
strong detergents and chemicals are all factors that affect the important natural barrier
protection of the skin and interfere with the normal bacterial flora.
Certain types of lotions and skin moisturizers can also have a negative effect.
In healthcare settings these are extremely important facts when it comes to hand-hygiene.
Faulty hand hygiene and faulty regimes that destroy the skin of hands are one of the
most important sources behind the spread of infections in healthcare settings.
Infection control must always have high priority
The health care system is constantly under financial restraints and it is feared that fewer
resources will be dedicated to infection prevention. It has also been shown that a consequence of an increasing workload on health personnel is failure to comply with hygiene
routines. It can be very difficult to trace the source of an infection or a transmission incident for both viral and bacterial infections.
Infections can also be transmitted in healthcare settings:
• between patient and personnel or vice versa
• to the patient via contaminated or inadequately disinfected instruments
• from the physical environment in the clinic
The three main transmission principles of so-called hospital-acquired
infections:
Endogenous infections. The patient is ”self-infected” with microorganisms. During
examination, nursing or treatment procedures, microorganisms which temporarily
colonize an individual patient can penetrate deeper tissue in which disease symptoms then develop. The longer a patient spends in a healthcare institution, the greater the risk to the patient of becoming colonized and then infected by his/her own
microorganisms.
Exogenous infection. The patient is infected by ”external” microorganisms that are
transmitted to patients, e.g. via the hands and clothes of the staff, or they may be
inhaled or swallowed. Microorganisms can also be transmitted via blood, transplanted organs or contaminated instruments.
Infected patients transmit microorganisms to the staff. This can occur when staffs
are in contact with infected body fluids, through puncture wounds or cuts, or are
subjected to droplet infection, e.g. through coughing or sneezing.
Several factors influence the risk of patients’ acquiring infection while receiving
health care:
Medical care is becoming increasingly advanced and complicated procedures are
carried out on gravely ill patients who are highly susceptible to infection .
More and more patients have impaired immunity and therefore run a greater risk of
developing infections caused by otherwise ”benign” microorganisms.
Patients whose nursing care and treatment are resource intensive are increasingly
being moved from major hospitals to smaller hospitals and into home care.
People who are unable to care for themselves are increasingly being cared for in
their own accommodation, e.g. in nursing homes.
Limited availability and decreased availability of single rooms or isolation rooms for
inpatients reduces the potential for stopping the spread of gastrointestinal and other
diseases.
There is concern that microorganisms with reduced sensitivity to antibiotics will increase because of uncritical use of antibiotics and inadequate hygiene routines.
Preserve barriers and minimize invasion
An intact skin/mucosal barrier is essential to prevent the establishment of infections.
With the very best intentions, common day-to-day healthcare procedures involve measures and treatments that will break, weaken or alter the body’s first line of defense – the
skin and mucosal barrier. Proper precautions must be taken to prevent and minimize the
negative effects of interventions as much as possible. This includes aseptic barrier
techniques and the use of carefully cleaned, disinfected and sterilized instruments and medical devices.
Inflammatory reaction – a state of emergency
Inflammation is the body’s response to infection. Inflammation is characterized by redness, swelling, precipitation of fibrin and the accumulation of white blood cells.
Inflammation is the body’s means of ”declaring a state of emergency” in a localized area.
The process increases the blood flow through the area, facilitates transport of the cells of
the immune defense system to the area, increases metabolism – creating nutrition and
oxygen for the cells and functions which will defend the body and subsequently repair the
damaged area.
With respect to hygiene and infection protection, it is particularly important to note that
inflammatory responses are not only triggered by living microorganisms, but also to a
great extent by the toxins from microorganisms.
Intruder versus defense - a race against time
Every infection is a race against time between the capacity of the microorganism to settle,
multiply, spread and cause disease and the ability of the host’s immune system to control
and eliminate the infective agent. A delayed immune response can give a decisive advantage to rapidly growing microorganisms, but it also gives the microbe the opportunity to
shed from the host in larger amounts.
Killing the host is a bad outcome for the microorganism – in evolution this will be a dead
end. A successful microbial parasite gets what it can from the host without causing too
much damage or makes sure to rapidly infect as many individuals as possible before killing the host.
At any given time, 1.4 million people worldwide
suffer from infections acquired in hospitals.
Hand hygiene is the most essential measure for
reducing health care-associated infection and the
development of antimicrobial resistance.
It is important to stress that hand hygiene is not only
important in direct patient care activities but in all
healthcare-related procedures including: cleaning,
disinfection,
sterilization,
storage,
cocking,
transport, logistics...
Sterilization can never compensate for bad cleaning,
bad storage or bad transport.
A chain is never stronger than its weakest link...
Facts and features
Important definitions: cleaning, decontamination and disinfection
Cleaning involves the removal of soil, organic substances and other residues from a
surface or item. Cleaning in itself do not comprise any microbial killing action and should
therefore not be confused with decontamination and disinfection.
Cleaning simply means that all visible soil is removed from an item, but this item may still
be contaminated with harmful microorganisms.
However, if the cleaning procedure is carried out under certain conditions, e.g. in washerdisinfectors, the process may also include decontamination and disinfection.
Decontamination is a term used to describe a process capable of rendering an item
(medical device, instrument, surface) safe to handle. Decontamination does not necessarily
mean that the article in question is safe for patient use.
Decontamination involves cleaning, i.e. all harmful substances must be removed from
the items. This does not necessarily mean that all microorganisms are killed; they might
merely be reduced to a ”non-hazardous” number. This means that the article is clean at
this very moment but that it can become ”recontaminated” if all the microorganisms are
not inactivated through a disinfection process.
Disinfection is generally a process that inactivates (kills) nearly all recognized pathogenic
microorganisms but not all microbial forms (bacterial endospores) on inanimate objects.
Disinfectants are germicides intended to be used solely for destroying microorganisms
on inanimate objects such as medical devices or environmental surfaces. The disinfection
process only kills the microorganisms on items but does not necessarily mean that the
items are clean.
Summing up the decontamination process of instruments and other medical devices, this
process must start directly after usage. If the instrument is surgical, it must be immediately
wiped or rinsed in the operating theater, in order to remove most visible soil. After that it
should be kept in a moist environment so that possible remaining biofilm/bioburden will
not dry on the instrument. Soil is much more difficult to remove after it has dried.
Upon arrival at the sterilizing unit, the instrument must be cleaned as an additional part
of the decontamination process followed by disinfection and, if required, packaging and
sterilization.
Conclusion
Cleaning is a type of decontamination
Decontamination is a process to remove or inactivate harmful substances. Decontamination must always involve cleaning, but not necessarily disinfection.
Disinfection is a process to destroy the microorganisms possibility to cause infection.
It is a process to inactivate or kill, but does not necessary include cleaning. Disinfection is not a decontaminating process. After disinfection an item can still be soiled
with dead/inactivated microorganisms and other debris (contaminated).
In reprocessing instruments: cleaning, decontamination and disinfection must be carried out in the right chronological sequence. In washer-disinfectors with automated
processes, all these steps are included.
Cleaning – the most critical stage in all disinfection and sterilization
procedures
Cleaning: the prerequisite for sterilization
The most effective stage of any decontamination procedure is thorough physical cleaning,
which should accompany or precede all disinfection procedures. Most equipmentassociated infection is due to inadequate cleaning and disinfection.
Limited anti-microbial effect
Cleaning involves the removal of organic substances and other residues from a surface
or item, but cleaning in itself has no microbial killing action and should therefore not be
confused with decontamination and disinfection.
However, certain cleaning procedures, e.g. in washer-disinfectors, also include
decontamination and disinfection.
“Bioburden”
The term “bioburden” is most often defined as the microbiological load, e.g. the number of
contaminating organisms in the product/item prior to cleaning, disinfection and sterilization.
An item heavily loaded with biological material will be more difficult to sterilize than one
that is only lightly contaminated. Medical devices requiring sterilization or disinfection must
therefore be thoroughly cleaned to reduce organic material or bioburden.
Bioburden can also be biological materials such as blood, mucous, fluids, feces, etc,
and when present on items to be processed for reuse, will contribute to failure of the
disinfection or sterilization procedure.
Don’t trust endospore testing blindly
Rigorous sterilization processes capable of killing exposed bacterial endospores may not
kill even relatively delicate microorganisms if they are protected by extraneous organic
material.
Biological indicators in the form of endospores (Bacillus Stearothermophilus, Bacillus
Subtilus) are often used to check the function of sterilizers. This indicator will only reveal
whether the process is capable of destroying just the endospores in the package or
container where the indicators are situated. If a heavily soiled instrument is processed in the
very same cycle and the bioburden on the instrument contains entrapped microorganisms,
the instrument will not be sterile after the process. The biological test is nothing but an
indicator! The result of the sterilization cycle depends on how accurately the instruments
have been treated by the personnel before the sterilization process.
Facts and features: How should cleaning best be carried out ?
Physical cleaning can be achieved by:
• scrubbing of instruments with soft brushes and proper detergents;
• ultrasonic cleaning through so called cavitation effects;
• in washer-disinfectors through a very high water flow at high pressure.
The use of washer-disinfectors is described in detail in the chapter covering disinfection.
Manual cleaning
When cleaning instruments and other medical devices manually, they should be scrubbed
with soft brushes using proper detergents. The water must be changed at regular intervals
and the articles rinsed in running water in between.
Abrasive agents and/or household detergents should not be used in healthcare contexts;
although they are excellent cleaners, they are intended for a completely different
purpose.
For household dishwashers the most common cleaning agents are high alkaline to
facilitate the removal of grease. High-alkaline detergents are more aggressive and prone
to cause corrosion. In healthcare contexts, high-alkaline products destroy the surfaces
of delicate instruments and also cause corrosion (uneven surfaces) that facilitates the
adhesion of soil and biofilms.
Instruments and articles used for medical purposes are often soiled with both proteins
(blood, serum albumin, saliva etc), lipids (body fats) and carbohydrates. Gram-negative
bacteria are much fattier (contains more lipids in the cell membrane) than gram-positive
types, where the cell membrane mostly consists of protein and carbohydrates.
Proteins require low temperatures in the cleaning process, since they coagulate at
high temperatures. Coagulated proteins can then become a protective shield for other
contaminants. Lipid components (fat), on the other hand, require high temperatures to be
dissolved. To avoid coagulation of protein, temperatures between +30°C and +40°C are
recommended.
Stepwise cleaning with water at different temperatures will therefore be necessary.
This must also be done with detergents that have a documented effect over the whole
temperature range used during the cleaning procedure.
If items are heavily soiled, it is much better to have a longer contact time (soaking) with
the detergent of choice rather than increasing the concentration of detergent or using
abrasive methods.
All brushes and other aids used to clean the instruments must also be kept clean and
decontaminated between usage.
After cleaning, the instruments and articles should not be dried by wiping with cloth, they
should be left to dry by themselves in a safe environment, free from dust, humidity and
other factors that might recontaminate the items.
Cleaned devices should only be handled
after proper hand hygiene and hand disinfection!
Physical cleaning is the key
Physical cleaning is the most important step in a disinfection and sterilization process.
Physical cleaning means the use of mechanical (kinetic) energy. The aim is to remove
residual bioburden and biofilm from all surfaces of the instruments/articles. This must be
done without harming and destroying the surface of the items.
Let the water do the job
It is not the physical cleaning per se that removes the bioburden. The most important
function of the physical cleaning is that it damages the biofilm, tearing away parts of it and
removing superficial layers of the biofilm. This facilitates for the cleaning liquid to penetrate
into the bioburden, the most important cleaning liquid being water. It is actually the water
molecules that finally remove the bioburden from the surface.
Don’t use hands
The process of manual cleaning must involve thorough scrubbing of all the surfaces of the
item and rinsing of the item in clean water. It is important to stress that manual cleaning
requires a high level of training and is time-consuming.
Automated processors offer the safest, most reliable option, provided they are suitably
monitored and maintained.
Manual cleaning should be restricted to situations when automated methods
are inappropriate or unavailable.
Chemicals or water?
Chemical disinfectants are, in most cases, only intended to kill microorganisms, not
to remove biofilm. In combination with chemical substances, the physical cleaning is
important in order to get the disinfectants into the deeper layers of the biofilm.
On surfaces that have been contaminated, mechanical cleaning with water and detergent
removes around 80% of all microorganisms. If a disinfectant is used, it is possible to remove
around 90-95%. The advantage of using a disinfectant is that this procedure breaks the
chain of transmission of infection. The advantage of water is its wetting capabilities, due
to the unique structure of the water molecules.
However, there are a few disinfectants that actually penetrate and by physical action
destroy the bioburden. Such chemical disinfectants, which work under certain conditions,
will be described in a separate chapter.
Facts and features: Ultrasonic cleaning
An effective physical force
In ultrasonic cleaning, the physical effects on the biofilm are caused by a phenomenon
called cavitation. If generated in fluids, high-frequency sound waves (ultrasound) create
shock waves that tear away both biological material as well as inorganic soil from the
articles being processed, so that cleaning agents can reach the surfaces of the items.
The forces in the shock waves in the ultrasonic cleaner (the cavitation effect) will be so
strong that they not only tear away the soil on processed articles, they also affect the
surfaces of these articles, causing smooth instrument surfaces to become uneven. This
in turn makes the instrument surface rough and pitted, which increases the possibilities
of microorganisms and soil to attach to the instruments, also making them more difficult
to clean by increased number of ultrasonic cleaning processes.
Some types of instruments should never be processed in ultrasonic cleaners due to the
risk of causing rough surfaces. Drills for bone implants are one example: a rough surface
will cause increased friction between the drill and the bone structure during use. Bone is
extremely sensitive to increase in temperature. An increase in temperature of +5°C can
cause local bone necrosis and thereby the loss of the implant.
Presoaking of instruments before the ultrasonic cleaning is essential. Materials that will
harden and stick to the instruments (bone cement etc) must be removed directly at the
point of use. If allowed to harden on the instruments, such materials will be impossible to
remove without destroying the instrument.
When using ultrasonic cleaners, detergents specifically designed for this purpose should
be used. The strong shock waves created by the ultrasound also affect the chemicals in
the detergents.
The strong shock waves also cause an increase in temperature. This is why certain types
of disinfectants must never be used in ultrasonic cleaners. Disinfectants containing alcohol
entail a risk of explosions at elevated temperatures.
Because of the increase in temperature, there is a risk of coagulation of protein that
can occlude microorganisms if the instruments are not pre-soaked and carefully rinsed
before the ultrasonic cleaning.
After ultrasonic cleaning, instruments should be thoroughly cleaned and rinsed again in
order to make sure that all possible contamination from water in the ultrasonic bath is
removed. This cleaning should then be followed by disinfection and sterilization of the
instruments.
Ultrasonic cleaners have a limited lifetime. To be effective they must generate highfrequency sound waves within a certain range. If the frequency of the sound waves is too
low, the cleaning process will not be effective. The cleaning device should therefore be
checked at regular intervals with specific process challenge devices.
Why not manual cleaning ?
There are several reasons for preferring automated processes if possible. Manual cleaning
in healthcare settings requires adequate training and skills.
It has been shown that hand-washing of items in still water reduces the microbial
bioburden. However, although the hand-washing procedure is effective in reducing the
microbial levels deposited on the surgical instruments, the risk of recontamination from
microorganisms in the water increases rapidly unless the water is changed frequently.
In manual washing of instruments and other medical devices, great accuracy most be
attended to follow precise guidelines about regular changes of water, water temperature,
concentration of detergents, rinsing procedures etc. Also the personnel must be well
protected against splashing, puncture wounds etc.
Different actions needed to remove fat, proteins and carbohydrates
Instruments and articles used for medical purposes will be soiled with both proteins
(blood, serum albumin, saliva etc), lipids (body fats) and carbohydrates. Gram-negative
bacteria are much fattier (contain more lipids in the cell membrane) than gram-positive
types, where the cell membrane mostly consists of protein and carbohydrates.
Proteins require low temperatures in the cleaning process, since they will coagulate at
high temperatures. Coagulated proteins can then become a protective shield for other
contaminants. As a contrast, lipid components (fat) require high temperatures to be
dissolved.
Stepwise and tailor-made cleaning a necessity for success
In the washer-disinfector it is therefore important to have detergents (tensides) that can
do their work in a wide range of temperatures. They should have an anti-protein action at
low temperatures and an anti-lipid action at higher temperatures.
The cleaning agents are often tailor-made so that different modes of action will appear at
different temperatures. Some detergents may be anionic in a certain temperature range
and cationic in another. There may also be release or activation of enzymes at a specific
temperature or pH-level.
Household cleaning agents are in most cases corrosive and remove soil through alkaline
activity. This is not desired on medical devices. Detergents for medical cleaning purposes
are delicate, sophisticated and tailor-made agents.
Facilitate water penetration
The importance of water penetration and the wetting of surfaces is one of the reasons
why washer-disinfectors are so extremely effective. Through the high pressure and large
flow, water is actually forced in to the bioburden.
Washer-disinfectors and the need for delicate detergents
In enzymatic detergents, specific enzymes have been added to the tenside molecules
to give additional effects. Washer-disinfectors clean the instruments at elevated
temperatures. Normal household detergents lose their efficiency or are destroyed at these
temperatures.
Facts and features about disinfection
Decontamination is a term used to describe a process capable of rendering an item
(medical device, instrument, surface) safe to handle. Decontamination does not necessarily
mean that the article in question is safe for patient use.
Disinfectants are germicides intended to be used solely for destroying microorganisms on
inanimate objects such as medical devices or environmental surfaces.
Disinfection procedures lack the sporicidal power of sterilization. The margin of safety
is much larger in a sterilization procedure since disinfection does not ensure the same
overkill as sterilization.
Disinfected objects should be safe to use for patients and personnel alike. However,
different levels of disinfection can be applied, depending on the intended use and purpose
(see below).
Antiseptic germicides are agents used on skin, in or on living tissues with the purpose
of inhibiting or destroying microorganisms. There are, however, substances that can be
used both as disinfectants and antiseptics, e.g. alcohols.
Cleaning involves the removal of organic substances and other residues from a surface
or item. Cleaning in itself does not cover any microbial killing action and should therefore
not be confused with decontamination and disinfection.
However if the cleaning procedure is carried out under certain conditions, e.g. in a washerdisinfector, the process may also include decontamination and disinfection.
Chemical agents should only be considered when physical properties such as mobility,
shape, size and weight of equipment make other disinfection processes impractical or
even impossible.
Manual cleaning and disinfection should be restricted to situations when
automated methods are inappropriate or unavailable.
Automated processors (washer-disinfectors) offer the safest, most reliable
option, provided they are suitably monitored and maintained.
Disinfection: How different disinfection procedures work and why
moist heat is a better choice than chemistry.
When costs and quality are important
Disinfection and sterilization processes are costly, so it is important to choose the
appropriate method to achieve the best possible results and at the same time to cause
the least damage to the items in question.
In terms of cost-efficiency, there are many parameters that need to be taken into account:
equipment needed, personnel, training and level of knowledge required, process time,
logistics, turnover time, media (power, water, steam), sewage handling etc.
More instruments or efficient disinfection and sterilization equipment ?
More rapid disinfection and sterilization processes result in shorter turnover times of
items, thereby minimizing the need for instrument stock. In every healthcare context, it is
important to critically evaluate all the different aspects of disinfection and sterilization and
how these functions can best be integrated with all other clinical functions.
Too many instruments – a common problem
The safety margin of the decontamination is largely determined by the type of equipment
and the kinds of procedures used at the clinic. A very important issue, one that is often
overlooked, is the logistics of instruments. A common problem in many healthcare settings
is an abundance of instruments which, apart from the significant additional cost, makes it
more difficult and time-consuming to keep track of all instruments and to make sure that
storage and sterile conditions as well as packaging/wrapping conditions are maintained.
It is always necessary to carry out an inventory of instruments and items in stock. Manual
inventories are highly manpower-consuming.
Common confusions – sterilization versus disinfection
Sterilization is the use of a physical or chemical procedure to destroy all microbial life,
including large numbers of highly resistant bacterial endospores.
Disinfection is generally a less lethal process than sterilization. It eliminates nearly all
recognized pathogenic microorganisms but not all microbial forms (bacterial endospores)
on inanimate objects.
Facts and features: Water and the efficacy of washer disinfectors
Facilitate water penetration
The importance of water penetration and the wetting of surfaces is one of the reasons why washerdisinfectors are so extremely effective. The high pressure and large flow actually forces water into the
bioburden.
Negative charges – one of nature’s wonders
The surfaces of a bacterial cell are negatively charged, as are the surfaces of nearly all other cells. Most
non-biological surfaces are also negatively charged (left figure below). This is either because the surface
accumulates organic material from the surroundings or because the surface itself is negatively charged due
to its own chemical components – or both.
A cloud of 10,000 electrical charges.
Since both the bacteria and the surface are negatively charged, they ought to repel each other. However,
the surface and the bacteria attract positive ions from the immediate environment, forming a surrounding
“cloud” of positively charged particles. Airborne bacteria can carry up to 10,000 electrical charges (righthand figure below).
Sharing electrical clouds
What attracts the bacterial cells to the surface is the possibility that the two opponents can share each
other’s clouds of positively charged particles (left figure below). However, if the bacterial cells get too close
to the surface, the so-called electrostatic forces (equal electrical charge) will cause repulsion. If, by chance,
the bacterial cell could overcome these repellant forces and get even closer to the surface, a very strong
bond will arise.
One way to get the cell closer to the surface is through compression of the volume of the surrounding cloud
of positively charged particles. This will actually happen if the amount of ions (salt, calcium etc) increases
in the liquid (as in the picture below with a high concentration of sodium chloride). Increased ionic strength
thereby reduces the electrostatic repulsion (right-hand figure below).
When using detergents it is important to follow the supplier’s recommendations. Over-dosage
can interfere with the whole cleaning process by helping bacteria to stick more firmly to the
items to be processed.
Three levels of disinfection depending on the purpose of the procedure
High-level disinfection is a procedure with a demonstrated level of activity against bacterial
endospores. High-level disinfection does not necessarily destroy large numbers of highly
resistant bacterial endospores, as is required of sterilization procedures.
High-level disinfection can be used to treat certain medical devices. The total absence
of bacterial endospores cannot be ensured, but it has been shown that the numbers of
spores on items subjected to such treatments are generally very low.
The sporicidal effect of high-level disinfection depends on what type of disinfection
procedure is being used and how it is carried out.
High-level disinfection should not be confused with a sterilization process, although it is
very close to being one. High-level disinfected products lack the margin of safety provided
by sterilization and also items cannot be wrapped. A sterile item shall be sterile at the point
of use, which requires proper wrapping. A sterilized medical device without wrapping is
the same as a high-level disinfected device.
In the USA, the Environmental Protection Agency (EPA) uses the term sterilants for the
same types of germicides that the Centre for Disease Control and Prevention (CDC) call
high-level disinfectants. Sterilants must not be confused with methods for sterilization
Intermediate-level disinfection refers to procedures that are not necessarily capable of killing
bacterial endospores, but which do inactivate Mycobacterium tuberculosis. Mycobacteria
are more resistant to disinfection than ordinary vegetative bacteria. Intermediate-level
disinfection is also effective against fungi as well as naked and enveloped viruses.
Low-level disinfection cannot be relied on to destroy, within a practical period of time,
bacterial endospores, mycobacteria, all fungi and naked viruses, but it inactivates
vegetative bacteria, most fungi and enveloped viruses
Chemistry or energy – advantages and disadvantages
Disinfection may be achieved through two basic methods: the use of chemical substances
or the transferal of energy (heat or irradiation).
Chemical disinfection offers major advantages in situations with sensitive medical devices
that will be severely affected, destroyed or altered if submitted to elevated temperatures.
Disinfection of skin and mucosa must also be done by the use of proper antiseptic
substances.
The greatest disadvantages of chemical disinfection are, of course, handling hazards and
environmental aspects.
In healthcare contexts, the use of ultraviolet light is a method for transferral of energy
through irradiation. Ultraviolet irradiation is inefficient as a disinfectant, its major important
use being inhibition of bacterial growth in water systems. Ultraviolet light is also used in
safety hoods in virology laboratories. There is a potential risk for damage to the eyes and
skin.
The preferable choice of energy transferal is the use of heat, the most effective agent
being water either in the form of water or saturated steam (moist heat).
The advantages of heat transferal through the use of water are availability, controllability,
efficiency and ease of use.
Facts and features: Water and the efficacy of washer disinfectors (continued)
Distilled water works best
Bacterial cells are not only attracted to different surfaces, but also to each other through the very same
phenomenon of electrical fields as described above.
Adding salt or ions to a bacterial suspension causes
bacterial cells in a planctonic phase to stick together,
forming aggregations that are heavy and sink to the
bottom of the suspension. It also helps bacterial cells
to stick even more tightly to a surface.
Adding small amounts of ions or salt to a solution,
however, destabilizes the bonds. But if the
concentration is too high, it will have the opposite
effect. The concentration needed differs between
ions.
This is the reason why water quality is so extremely
important in the cleaning process. The very best
results are actually achieved by using deionized
(distilled) water.
The cleaning power of water
The reason why water in itself is a very good cleaning agent lies in the structure of the water molecule.
Water, H2O, is a molecule with three atoms, two of them hydrogen and one oxygen. The water molecule is
V-shaped, with the two hydrogen atoms at the open ends and the oxygen atom at the point.
This gives the water molecule the unique characteristic of a dipole (left figure below), with one negatively
charged part (oxygen) and one positively charged part (hydrogen).
Dipolarity a useful quality
The dipolarity of the water molecules can be compared with a magnetic needle having a north (”negatively
charged”) and a south (”positively charged”) side. It is obvious what happens when trying to put the two
equal sides of two magnets together – there will be a strong repulsion (figure in the middle below).
A cloud of water molecules
During the cleaning process, the water molecules gather around the instruments and articles with the
positive side of the molecule facing the surface and the negative side facing the surroundings (the same
phenomenon described above as a cloud of positively charged particles). The water molecules form the
same “cloud” around the bacteria and the soil to be removed from the article in question.
The earlier described electrical double layer now consists of water molecules on both counterparts. The
negatively charged oxygen side of the water molecules now sticks out from both the surface of the articles
and from the surface of the bacteria (soil) and thus facing each other. This time, both negatively charged sides
of water molecules repel the bacteria and the soil from the surface. This is actually a strong “mechanical”
cleaning of the items being processed. The reason why water is such a good cleaning agent thus lies in the
dipolarity of the water molecule.
Beware of endotoxins
Disinfection and sterilization can be achieved by physical or chemical means, either by the
removal of microorganisms from an item or by killing the microorganisms on site.
If microorganisms are simply killed on site, toxic products such as bacterial endotoxins
and breakdown products will be left on the items.
Elimination of endotoxins continues to be a problem and standard methods of sterilization,
such as autoclaving, have little effect on endotoxin levels.
Moist heat / water should always be number one choice
Decontamination, cleaning and disinfection by thermal treatment is always preferable.
The easiest method is in an automated washer-disinfector that cleans and disinfects in a
single step.
Washer-disinfectors – the best method for cleaning and disinfection
Washer disinfectors have a double function: first a thorough cleaning process followed by
heat disinfection where the water temperature is elevated almost to boiling point.
Another key feature of washer-disinfectors is the extremely high flow of water, in terms of
both volume and pressure.
Washer-disinfectors are sophisticated medical devices. The relation between the increase
in water temperature and process time is of great importance and must be well calibrated.
There are a number of circumstances that the manufacturers have to take into account.
These circumstances also call for regular process validation.
Sterile goods in washer-disinfectors after completed cycle
If handled (and especially if loaded) with goods as intended, and if maintained properly,
the final results of washer-disinfectors will actually be sterilized goods.
The major difference between washer-disinfectors and sterilizers is that washer disinfectors
remove bacterial endotoxins and breakdown products on items as well as chemical
residuals.
The major disadvantage of washer-disinfectors is than even if the process results in
sterilized products, the problem is how to get them out of the washer-disinfector in a dry
and sterile condition and also how to maintain sterility.
Sterilization adds wrapping possibilities for safe handling and storage
What the subsequent sterilization process adds is the possibility of wrapping the
products.
Logistics, transport and storage makes it necessary to add a safe wrapping to washerdisinfected items and this can only be achieved in a sterilization process.
Facts and features: Water and the efficacy of washer-disinfectors (continued)
Wetability and adhesion
There is of course a difference between different types of material both when it comes to the tendency for
bacteria and soil to attach to the surface and also the wetability (how well water can wet the surface).
Among other things, surfaces (materials) with a high number of iron (Fe) ions are more difficult for the
bacteria to be attracted by and adhere to.
It is also more difficult for bacteria and soil to adhere to a wet wooden cutting-board than if the surface is
dry.
Difficult to cover the whole surface
Wetability refers to how easy it is for a layer of water to cover an entire surface. Water on an oily surface is
difficult – the water is repelled from the surface and forms larger round drops. This also has to do with the
surface tension and surface energy of water.
Surfaces with wetability are referred to as hydrophilic (water-loving, from the Greek philien = love,) or
hydrophobic (water-fearing, from phobos = fear).
The more hydrophilic a surface is, the more effectively the water molecules can cover the entire surface.
Consequently it is simpler for water to expel soil and bacteria deposits from a hydrophilic surface than from
one that is hydrophobic. In general metal is hydrophilic and plastic hydrophobic. Metal instruments are
therefore better in surgical settings.
Detergent – water’s little helper
The main reason for the use of detergents (tensides, surfactants) is to help the water molecules to wet
the surface. This works partly by making the surface more hydrophilic and partly by lowering the surface
tension of water. (From the Latin detergeo = cleaning, and tendo = tension.)
This effect can easily been seen when comparing what happens when lifting a glass upside down out of a
sink with water and then with water to which detergent has been added.
Like water, detergent molecules have two different sides, one hydrophilic and the other side hydrophobic.
The detergent can thus act as a link between the water molecules and the hydrophobic surface.
The usage of electrical charges – anion or cation
Depending on the intended use and the desired mode of action of the detergent, the hydrophilic end of the
molecule can either have an electrically positive charge or an electrically negative charge.
If negatively charged, it is an anionic detergent. If the hydrophilic side of the detergent molecule is positively
charged, it is a cationic detergent.
Detergents for household use or healthcare settings – two different agents
There is a crucial difference between anionic and cationic detergents when it comes to their use in healthcare
contexts. Household detergents are in most cases anionic. Detergents for the cleaning of items that should
accompany or precede all disinfection procedures should be cationic.
Cationic tensides (detergents) will attract and adhere to the cell membranes of bacteria (the same principle
as described above with a cloud of positively charged particles). Cationic cleaning agents then interfere with
and destroy the bacterial cell membrane.
Cationic cleaning agents have a double function – both acting as a wetting agent (simplifying the work of
the water molecules in their cleaning action) and also through a direct bacteriostatic (inhibiting) effect.
Household detergents should therefore not be used in healthcare settings; they are excellent cleaners but
intended for a completely different purpose.
Acidic or alkaline
The pH of the detergent is also of importance. There are acidic detergents, but more often low- or highalkaline detergents. High-alkaline detergents are more aggressive and prone to cause corrosion. For
household dishwashers, the most common cleaning agents are high alkaline to facilitate the removal of
grease on items. In healthcare contexts, high-alkaline products destroy the surfaces of delicate instruments
and also cause corrosion (uneven surfaces), thereby facilitating the adhesion of soil and biofilms.
Household products are intended for another type cleaning, not to compare with healthcare
settings, e.g. hospital cleaning.
The force of massive water flow
An important feature of washer-disinfectors is the extremely high flow of water, in terms of both volume
and pressure. The massive flow of water spraying all items in the washer-disinfection process results in
very effective physical (mechanical) cleaning. The washer-disinfection cycle should always start with cold
water. The in-flowing water must be maintained at a temperature low enough to preclude the occurrence
of protein coagulation. Temperatures higher than +45°C (+113°F) can cause protein coagulation during the
flushing stage and cause cleaning problems in the further process.
Program phases in
washer disinfector
1. Pre-rinse
2. Cleaning
3. Post-rinse 1
4. Post-rinse 2
5. Final rinse
6. Disinfection
7. Drying
How leathal is hot water
- killing temperature for
certian microorganisms.
HIV
+56°C
Most bacteria
+65°C
(Strepto-, staphylococcus)
Mycobakteria
+72°C
(Tuberculosis – TBC)
Hepatitis B-virus +85°C
(HBV)
Endospores
+121°C
(Bacillus stearothermophilus)
Note: Contact time factor not included !
In every thermal disinfection and sterilization cycle there is always an initial microbial activation phase before
the temperature has become high enough to inactivate and kill the microbes. In a humid (wet) environment,
germination of several species of endospores reaches its maximum in the temperature interval from +45°C
(+113°F) to +52°C (+127°F). Slower changes in temperature parameters at specific temperature intervals
in the washer-disinfection process will favor outgrowth (germination) of endospores. Bacteria are killed at
much lower temperatures than the corresponding endospores. The washer-disinfector process is thus
“indirectly sporicidal”, killing the endospores by first stimulating them to grow out in their vegetative bacterial
stage.
The use of proper detergents is important in washer-disinfectors. They should have an anti-protein action
at low temperatures and an anti-lipid action at higher temperatures. Most detergents intended for washerdisinfectors also have an enzymatic activity. The types of enzymes used normally have their highest activity
at around +50°C (+122°F). The cleaning agents are often tailor-made so that different modes of action will
appear at different temperatures. In the cleaning phase of the procedure, the articles are washed in water
at temperatures up to +70°C (+158°F). Once the cleaning phase is completed and before the disinfection
phase, residual chemicals (detergents) must be removed from all items. The residual level which can be
tolerated will depend upon the nature of the chemical and the intended use of the product being cleaned.
Elevated levels of chemical residuals on articles and goods can lead to adverse and, in the worst cases,
toxic reactions and thus adversely affect treatment results.
In the final disinfection phase, the water temperature increases, providing thermal disinfection of the
load. In the temperature range of +85°C (+185°F) to +95°C (+203°F), pathogenic microorganisms are
inactivated or killed. Bacterial endospores survive these temperatures, but if the procedure has worked
as intended, the endospores will be inactivated, tricked into germinating, and then killed (in its bacterial
form) or simply washed away. In order to ensure inactivation of viruses, particularly heat-tolerant ones,
it is now recommended that the water temperature during the disinfection phase should be just over
+90°C (+194°F). Even though there are international standards as well as European and other norms for
washer-disinfectors, national regulations may differ. The disinfection capacity does not depend solely on
the temperature; the contact time must also be considered. Lower disinfection temperatures require longer
contact times (disinfection phase).
Facts and features:
The most common chemical substances for chemical disinfection
Aldehydes (benzaldehyde, glutaraldehyde, succinaldehyde, formaldehyde).
These have a broad antimicrobial spectrum, and cause little damage to materials. The disadvantages are
allergenic, toxic and environmental aspects. Aldehydes have a strong odor, perceived by many as irritating
and disturbing.
They are effective against Gram-positive and Gram-negative bacteria, fungi, encapsulated and naked
viruses, but have a slow (weak) effect on tuberculoid bacteria (mycobacteria). Aldehydes are sporicidal
(can be used for so-called cold sterilization) with a contact time (immersion) of at least 6 hours, when the
aldehyde is fresh.
Aldehydes should be used with caution – they have a coagulating effect on blood and bind tissue on
surfaces. For this reason, cleaning of inanimate objects is extremely important before exposure to aldehydes.
If biological materials become bonded to surfaces by aldehydes they will be almost impossible to remove
without the use of abrasive cleaning aids, which also will destroy the surface of delicate medical items
(instruments).
Aldehydes (esp. glutaraldehyde) are very good disinfectants. They are relatively inexpensive, non-corrosive
and have excellent material compatibility. Inactivation by organic material is very low. However, it is crucial
that aldehydes are used correctly and with great care.
Alcohols (ethanol, isopropanol, n-propanol). These have a broad antimicrobial spectrum, rapid effect against
most microorganisms, very rapid and good effects against mycobacteria (tuberculous), and do not damage
material. Alcohols are very appropriate for hand, surface and instrument disinfection. However, isopropanol
is less effective against non-encapsulated viruses.
For hand antisepsis, propanols must have a concentration of over 60v/v% (volume percent) or equivalent,
which is often attained by blending isopropanol and other alcohols, e.g. ethanol or n-propanol. Ethanolbased hand antiseptic agents should have an antiseptic effect corresponding to a concentration of 77v/v%
ethanol. For disinfection of surfaces and instruments ethanol has its optimal effect around 70v/v% and
propanol around 45v/v%.
Alcohols exert a strong and fast action against a wide spectrum of bacteria, fungi and viruses. They are not
influenced by interfering substances to any great extent.
Alcohols are of low toxicity, easy to use, environmentally friendly and economical. In a great number of
disinfection procedures, alcohol should be number one choice of substance. For skin disinfection there are
combinations with iodine or chlorhexidine.
Chlorhexidine (biguanide-derivative). This substance has a narrow antimicrobial spectrum, and is inactivated by soap. Special regulations must be observed for use, since the substance is toxic to nerve tissue.
Chlorhexidine is particularly effective on Gram-positive bacteria and to some extent on Gram-negative bacteria. Indications for usage are disinfection of skin and mucous membrane. Chlorhexidine is far too expensive for other uses than skin and mucous membranes, as much higher concentrations would be required
for disinfection of instruments, surfaces etc.
Chlorhexidine is pH-dependent and has its best effect in the pH range 5.5 –7.0, which corresponds well to
the pH of the skin. In higher concentrations and at elevated temperatures, +70°C (+158°F), chlorhexidine
has a sporicidal action, but causes formation of insoluble residues at +121°C (+249°F). Chlorhexidine is
therefore not a good alternative in combination with moist heat sterilization.
The great advantage of chlorhexidine is that the molecules will bind to biological membranes (skin, mucosa)
and exert a slow release of these bound molecules. The effect of this is continuous prolonged disinfection.
This is one of the reasons why a combination of chlorhexidine and detergent is highly effective for disinfection, e.g. of hands.
Chlorine compounds (hypochlorites, chlorine dioxide). This group has a broad antimicrobial spectrum,
rapid action, and are good for disinfection of large blood spills or for heavy contamination. They are corrosive to metals, less stable in standard solutions, and inactivated by organic matter. Chlorine compounds
are effective on Gram-positive and Gram-negative bacteria, mycobacteria, fungi, encapsulated and nonencapsulated viruses. They can be used for surface and instrument disinfection, as well as in dentistry to
disinfect impressions.
The mechanism of the bacteriocidal action of chlorine is the formation of hypochlorous acid which is responsible for the destruction of microorganisms.
Chemistry must never be first hand choice for items that could be processed
otherwise
The use of chemical disinfectants should be strictly limited. Unnecessary use of chemical
products is both expensive and inappropriate in view of the negative environmental effects
associated with many such products. Furthermore, with respect to some products,
inhalation or direct contact may be hazardous to health. Chemical disinfectants affect
living cells: thus they affect both the user and the environment.
Various disinfectants have different fields of application and should be used accordingly. It
is also important that the manufacturer’s instructions for use are always adhered to.
Antimicrobial resistance to chemical disinfectants
Development of resistance by microorganisms to disinfectant agents has been reported
for certain chemicals: quarternary ammonium compounds, chlorhexidine and triclosan.
The concentrations normally used in commercial disinfectants are, however, much higher
than those shown in laboratory testing to pose a risk of developing resistance. There are
no reports of the development of resistance to other chemicals than those mentioned
above. The importance of continuing studies and documentation of them is due to the
fact that they are common ingredients, e.g. in antiseptic soaps, cleaning agents, domestic
dishwashing detergents and in toothpaste.
It has been documented that there are cross-links between antimicrobial resistance to
chemical disinfectants and resistance to antibiotics. Increased antimicrobial resistance to
chemistry can also lead to development of antibiotic resistance.
There is every reason to be cautious with this type of chemical. It is also a further motivation
for preferential use of alcohol-based disinfectants rather than soap and water.
Be careful in choosing the appropriate agent
When using chemical disinfectants it is important to determine what type of disinfectant
will be the best in a given situation. There are several important factors that need to be
taken into account. Like all other chemical substances, disinfectants behave differently
under different conditions.
Different disinfectants have different fields of application and should be used accordingly.
It is important that the manufacturer’s instructions for use are always adhered to. A
chemical agent that has superb disinfecting capabilities in one area can be the wrong
choice in another. Alcohol concentrations intended for surface disinfection will not be
suitable for hand disinfection. Aldhehydes can have opposite effect in the presence of
biofilm. Chlorhexidine is both temperature- and pH-dependent. Hypochlorite is inactivated
by organic material. Phenolics are inactivated by hard water etc.
Facts and features:
The most common chemical substances for chemical disinfection (continued)
Hypochlorite solutions are the most widely used of chlorine disinfectants. They are cheap and effective.
Dilutions are unstable and should be freshly prepared daily. The shelf-life of prepared dilutions is further
decreased by light, heat and heavy metals.
Sodium hypochlorite must not be mixed with ammonia, acid or acidic body fluids (e.g. urine) as toxic
chlorine gas will be released. Chlorine dioxide does not react with ammonia.
Peracids – peroxides (esp. hydrogen peroxide) Peroxides have a broad antimicrobial spectrum. Peroxides
have a cleansing effect, particularly in wounds, through 1) rapid, strong release of acid (foaming) and
2) oxidation of organic debris. All peracids are corrosive to metals, and at high concentrations highly
irritant to skin and mucous membranes. Peroxides inactivate Gram-positive and Gram-negative bacteria,
(mycobacteria), fungi, encapsulated and non-encapsulated viruses. In 3% - 6% solution, hydrogen peroxide
(H2O2) is used for disinfection. The main areas are primarily disinfection of skin and mucous membrane
and wounds and dental impressions. There is some doubt about the effect on mycobacteria (tuberculoid
bacteria) and concentration needs to be elevated (7.5%) to ensure a tuberculocidal effect.
Hydrogen peroxide is nature’s own disinfectant. It is naturally present in milk and honey. In the human body
it is present in mucous membranes and in the mouth in saliva. White blood cells use hydrogen peroxide to
kill foreign cells before digesting them.
In higher concentrations hydrogen peroxide is sporicidal, and can be used for cold sterilization (in 30%
solution highly irritant and corrosive!). The activity is dependent on time and temperature as well as pH:
500 ppm (0.5%) at +37°C (+100°F) for 7 – 18 hours, and 35,400 ppm (35.4%) at +45°C (+113°F) for 12
seconds.
Hydrogen peroxide can be used in the vapor phase for sterilization of certain types of items and instruments
(see further in the chapter about sterilization).
Peracids – persalts (potassium persalts, sodium persalts). In this sub-group of peracids, peracetic acid is
a strong disinfectant with a wide spectrum of antimicrobial activity, even in the presence of organic matter.
This sub-group has a broad antimicrobial spectrum, and provides good preparations for disinfection of
larger blood spills or heavy contamination. Persalts represent a broad field of application, particularly in
the food industry (dairy, brewing, wine industries). Also corrosive (incompatible) to some metals, aluminum
anodized coatings become dull.
Pure aluminum, stainless steel, and tin-plated iron are resistant to peracetic acids. Plain steel, galvanized
iron, copper, brass and bronze are susceptible to corrosion and unfavorable reactions.
In powder form, persalts can have an irritant effect on the mucous membranes of the respiratory tract.
Effective on Gram-positive and Gram-negative bacteria, mycobacteria, fungi, encapsulated and non
encapsulated viruses. Indications for usage are instrument and surface disinfection, dental impressions.
Higher concentrations are required for use against mycobacteria.
Peracetic acids are unstable compounds. The breakdown products of peracetic acids are acetic acid,
hydrogen peroxide and water.
Peracetic acids are active in a very large temperature span: A 3% solution has a sporicidal effect even at
-40°C (-40°F) and at temperatures up to +85°C (+185°F). However, the sporicidal effect is of course timedependent.
They have their best effect in the pH range 5 – 8, with better activity at lower pH. Peracetic acids have a
synergetic effect with alcohols; adding small amounts (up to 20%) will increase the effect.
The advantages of peracetic acids are: absence of persistent toxic or mutagenic residuals or by-products,
no quenching requirement (no need for “dechlorination”), small dependence on pH and short contact
time.
Peracetic acids are effective in penetrating organic matter such as biofilms and thus more effective than
glutaraldehydes.
Peracetic acid has also been proven to be effective against helminthes and tapeworms (cestode) in the
treatment of sewage sludges.
Recent results with peracetic acid-based sterilizing solutions indicate that it might even be a safe and
effective means of prion deactivation on medical devices.
Peracetic acids are becoming more and more cost-competitive with chlorine
Chemistry must never be an alternative to moist heat
Chemical disinfectants as well as chemical sterilants can be useful in carefully selected
situations. For instruments and similar articles, chemical disinfectants must never be an
alternative to disinfection with moist heat in any situation where the latter is possible.
Chemicals can only be a complement – never an alternative – to sterilization procedures
with moist heat – a sterile instrument should be sterile at the point of use. This requires
a sterile wrapping for safe handling, transport and storage after the sterilization process,
and sterile wrapping is impossible after immersion in a chemical agent. To be handled as
sterile goods if chemistry has been the choice, chemical residuals must be removed and
the object then wrapped and processed through a sterilizing cycle using moist heat.
How effective are different substances ?
The efficacy of a chemical disinfectant should be stated on the packaging, on the directions
for use, on the list of contents or on the material safety data sheet.
“Bacteriocidal” indicates that the formula inactivates (kills) bacteria, whereas “bacteriostatic”
means that the preparation reduces but does not completely kill the bacterial flora.
Corresponding descriptions for virus and fungi are viricide / antiviral and fungicide /
fungostatic. The formulas are frequently tested for disinfectant effects with respect to:
Vegetative bacterial flora. This generally refers to the common non-sporing form of
the bacteria, e.g. pseudomonas and staphylococci.
Hepatitis B-virus. This is frequently used as a typical encapsulated virus and is
present in large amounts in infected blood. It is also a vigorous virus that can survive
for weeks and months in dried blood. A chemical disinfectant capable of inactivating
hepatitis B-virus is a good choice of preparation. Other examples of encapsulated
viruses are herpes simplex, cytomegalovirus and HIV.
Poliovirus. This is a good example of a non-encapsulated (naked) virus. Other
examples are hepatitis A virus, coxsackievirus and rhinovirus. Apart from hepatitis B
virus, poliovirus is usually also used for testing the disinfectant power of chemicals.
Naked viruses are more tolerant than encapsulated viruses to changes to the
environment, e.g. pH, the influence of protein-splitting enzymes and chemical
disinfectant agents. Encapsulated viruses are more sensitive to chemicals such as
soap and detergent..
Fungi. The effect of an agent intended for application in healthcare is usually tested
on Candida albicans.
Mycobacteria. The chemical disinfectant agent’s effect is usually also tested on
mycobacteria, e.g. Mycobacterium tuberculosis.
Facts and features:
The most common chemical substances for chemical disinfection (continued)
Quarternary ammonium compounds (benzalkonium chloride, ammonium salts). Are included in certain
alcohol-containing disinfectants to enhance the effect. Quarternary ammonium compounds have an
excellent cleaning potential and are used in combination with other chemcial disinfectants, usually alcohols,
of the order of 1% ammonium compounds.
Quarternary ammonium compounds are the most widely used cationic detergents and are used as antiseptic
agents as they inhibit bacterial growth. But quarternary ammonium compounds do not kill bacteria! Gramnegatives such as Pseudomonas can contaminate and grow in diluted solutions.
There are reasons to be cautious with quarternary ammonium compound-based detergents and antiseptics;
benzalkonium chloride is one of the leading allergens among healthcare personnel worldwide.
Phenolics (esp. carbolic acid). These were used already by Joseph Lister in 1867 as a germicide in operating
rooms, but no longer play a significant role as an antibacterial agent.
Phenolic disinfectants are considered to be low-to-intermediate-level disinfectants. They have a broad
spectrum of antimicrobial activity: Gram-negative and Gram-positive bacteria, fungicidal, tuberculocidal
and virucidal against capsulated viruses.
Due to their toxic properties, several undesired side effects and prolonged environmental degradation,
phenolics are not a first choice. Phenolics such as hexachlorophene have been banned for sale in a number
of countries. They are, however, still being used as cold-sore creams and throat lozenges.
Iodine and iodophores. Iodine is much more effective than chlorine but has several properties unsuitable for
clinical use: unpleasant odor, staining of skin, staining of laundry, solutions that are are unstable and irritate
tissue, painful in open wounds and allergenic.
Iodine at high concentration is poisonous and may cause serious damage to skin and tissues. In dilute
alcoholic solution or aqueous solution, it has limited use as a topical antiseptic.
Iodophores are chemical complexes of iodine that minimize the negative effects of pure iodine without loss
of germicidal efficacy.
One of the major advantages of iodine today is emergency purification of water, especially in rural and
underdeveloped countries. Iodine is a cysticide and works on parasites, e.g. amoeba. They can inactivate
viruses more completely than other halogens, but are a costly alternative.
Read the manual – use the proper product
The use of chemical disinfectants should be strictly limited. Unnecessary use of chemical products is both
expensive and inappropriate in view of the negative environmental effects associated with many such
products. Furthermore, with respect to some products, inhalation or direct contact may be hazardous to
health.
Chemical disinfectants affect living cells; thus they affect both the user and the environment.
Various disinfectants have different fields of application and should be used accordingly.
It is important that the manufacturer’s instructions for use are always adhered to.
Summary: pathways for disinfection
There are several different methods that can be used when reprocessing instruments. However, all the
steps listed in the picture below must be included in the process and in the correct chronological order:
The preferred method depends on several factors, e.g. the availability of personnel and equipment.
Automated processors (washer-disinfectors) offer the safest, most reliable option, providing they are suitably
monitored and maintained. As can be seen in the picture below, all steps are included in the washerdisinfector process. Manual cleaning and disinfection should be restricted to situations when automated
methods are inappropriate or unavailable.
If articles are NOT wrapped, the result even after sterilization will be high-level disinfected goods (upper
figure). Wrapping is necessary if the goods are to be sterile. Logistics, transport and storage makes it
necessary to add a safe wrapping procedure to washer-disinfected items and this can only be achieved in
a sterilization process. (lower figure).
Example: Decontamination can be achieved through rinsing, wiping, soaking or ultrasonic cleaning, followed by predisinfection, either chemically or through boiling, etc...
If a washer-disinfector is used, all steps are included in the process, but articles must always be decontaminated at the point of use
Facts and features about sterilization
Sterility Assurance Level – SAL. After a completed sterilization cycle the theoretical security level should be
SAL=10-6. This is often misinterpreted as only one living microorganism in one million sterilized items. The
correct interpretation requires some clarification.
The normal measurable contamination level of a used instrument is around 1 million microorganisms (106).
(Under normal conditions, the skin of the human body has around 1 million microbes per square centimeter). Let us suppose that the sterilization process starts with an instrument contaminated with 106 microorganisms (see figure 1 below). Presuming that the sterilizer is filled with a number of instruments having the
same contamination level to start with, during the sterilization cycle instruments are picked out at regular
intervals to measure the remaining number of living microorganisms. With increased sterilization cycle time,
the number of living microorganisms becomes lower; this can be measured until there are no more living
microorganisms left. The number of living microorganisms will now be zero. This is the point in time where
the curve (the blue line in the diagram) meets the x-axis in the diagram, and it takes X minutes to reach this
point, during which one can actually measure the number of remaining living microorganisms.
By doubling that time to 2X minutes in a mathematical calculation, another 106 microorganisms would be
theoretically killed, but now continuing from zero microorganisms ending up with 10-6. The extra time, to
achieve the killing of microorganisms beyond zero, is a margin of safety that forms the basis for calculating
sterilizer cycle times
The d-value (d1 in the figure) is a measure of the heat resistance of a microorganism. It is the time in minutes at a given temperature required to destroy 90% of the target microorganism (1 log cycle). Going from
106 to zero takes of six (6) d-values, and to assure a sterility level of SAL 10-6 would require twelve (12)
d-values.
In accordance with EN ISO 11138 the biological indicator (Bacillus Stearothermophilus) for steam sterilization with the use of moist heat should have a minimum population (number of spores in each test) of 105
cfu (at least 100 000 spores), and a D-value D121 not less than 1½ minutes (destroying 90% of the spores
every 1½ minutes).
Going from 105 endospores to zero will then require 5 x 1½ minutes = 7½ minutes and for assuring SAL
10-6 another six (6) d-values are needed (6 x 1½ minutes = 9 minutes). The total sterilization time (7.5 + 9
minutes) is thus 16½ minutes. In the European norm, 15 minutes is the minimum time at 121 °C, but most
manufacturers set their cycles to 20 minutes.
In figure 2, using the same type of microorganisms with the very same D-value as in figure 1 and having the
same length of sterilization time, but starting with a cleaner instrument (with only 101 (ten) microorganisms),
the sterilization process will result in a much larger safety margin.
The cleaner the instrument before sterilization (less bioburden), the safer the
result !
Sterilization: Adding wrapping for safe handling and storage
Sterile does not mean clean and safe for use
The benefits of a sterilization process can easily be lost if goods are not wrapped. Logistics,
transport and storage make it necessary to safely wrap high-level disinfected (washerdisinfected) items and this can only be achieved in a sterilization process for wrapped
goods.
Sterility is defined as the total absence of any microorganisms capable of reproduction.
There is confusion in the use of the term sterile; in the area of hygiene and infection
control it often refers to a medical device being clean, safe and free of disease-causing
microbes.
It is of great importance to fully understand that the term sterile means nothing less than
not being able to reproduce.
The term sterility, in itself, has nothing to do with being clean, free of endotoxins, free of
microbial residuals or being safe to use. In the internationally accepted definition, sterile
items should have a sterility assurance level (SAL) of 10-6. This definition of sterility as a
probability function does not assume that one in a million products is allowed to be nonsterile but admits a finite mathematical, statistical probability that microorganisms may
survive the sterilization process.
SAL calculations do not in any way define the amount of residual bioburden or the
amount of endotoxins or other biological residuals. SAL only refers to the death rate of
microbes.
Theoretical methods to prove sterility
There are no methods after the sterilization process to prove that the entire load is sterile
without destroying the whole load. Therefore the quality assurance has to be based on
so-called “process challenge devices” and theoretical, mathematical calculations on the
probability of a specific process resulting in sterile goods.
Proper cleaning and decontamination – the number one priority
For this reason it is important that the whole decontamination-disinfection and sterilization
cycle is validated in accordance with a quality assurance program. This must include
validation, qualification and process control of both the cleaning-disinfection procedure
as well as the sterilization process. They cannot be seen as separate entities – if articles
are not thoroughly clean, sterilization will fail.
Dangerous misunderstanding
There is a very common and dangerous misunderstanding that sterilization is the most
important part in the hygiene and infection control cycle. – It cannot be emphasized
enough that the most important part will always be cleaning !
Sterilization procedures combined with wrapping are essential for safe handling, storage
and transport, but sterilization can never be an alternative to cleaning. Cleaning and
subsequent disinfection (read: washer-disinfection) are always the most
important procedures when reprocessing instruments and articles for
sterile use.
This is of course on condition that the washer-disinfection process is performed as
intended and if proper maintenance and validation of the procedure are carried out.
Facts and features about steam sterilization
A tremendous amount of lethal energy
In order to understand correctly the sterilization process it is important to understand
how a steam sterilizer – sterilization with water vapor – functions. A basic prerequisite is
a sterilizer chamber with so-called saturated steam. Heating one liter of water from room
temperature to the boiling point requires approx 300kJ (kiloJoules).
When the water reaches the boiling point, all additional energy will be used to convert the
liquid water to steam and only when all the water has been converted to steam can the
additional energy be used to further raise the temperature. In this latter phase the temperature of the steam will increase. Converting one liter of boiling water to steam requires
2250 kJ.
If the saturated steam comes into contact with any object which is cooler than
the boiling point, the steam will condense, releasing its intrinsic energy. A prerequisite for this great release of energy is that the water changes phase from
saturated steam to liquid. It is this energy release that is used to sterilize the
items in the steam sterilizer.
1. The amount of energy (heat) needed to heat ice from -50°C to 0°C is 95 kJ.
2. At 0°C the temperature rise stops in spite of energy being continuously added. The added energy
is absorbed in the conversion when the water goes from solid (ice) to liquid state (water). The required melting energy is 335 kJ.
3. The water temperature will not increase until all ice is melted. To increase water temperature from
0°C to 100°C, 420 kJ of heat must be added.
4. At 100°C the temperature becomes constant again
The energy consumed until all fluid water is converted into steam is equivalent to 2250 kJ.
5. The temperature of the steam could be further increased – superheated steam.
Steam should be first choice.
Sterility may be achieved by various methods: heat, chemical and ionizing radiation. The
simplest method is heat sterilization. There are two methods: dry heat sterilization, i.e. use
of dry heat (usually a hot air oven or sterilizer), in which moist heat (steam) is used.
Dry heat is a slow process which requires high temperatures. The most definitive method
of sterilization is incineration which will carbonize (char) all organic material. Heating instruments red-hot over an open fire is a well-known ancient method of sterilization, and in
many situations still a useful method but unpractical for medical devices and also harmful.
Incineration has its major use in the handling of hazardous biological waste.
Today, the quickest, safest and most efficient method is steam sterilization. Steam sterilization is also inexpensive and cost-effective.
Without wrapping, logistics are impossible
Regardless of the method, the result of sterilizing procedures depends, among other
things, on the number of microorganisms and other biological material present on the
article before inactivation and the resistance of some microorganisms to the sterilization
process. The volume and composition of the bioburden on the articles to be sterilized
determine the amount of energy required for sterilization. The physical properties of the
materials to be sterilized are also of great importance: solid instruments, hollow items,
porous loads, volume and weight of the load etc.
Steam sterilization – the safest and most reliable method
Steam sterilization is more effective than other forms of sterilization because brief exposure to steam destroys most resistant bacterial species and heat is rapidly achieved
because of mass heat transfer as the steam condenses.
Steam sterilization requires exposure of each item to direct steam contact at the required
temperature and pressure for the specific time. Well-designed steam sterilizers deliver
steam to the bacterial sites throughout the load. The major problems during the process
are air evacuation, superheating and load moisture.
Virtually all air must be evacuated during pre-treatment so that the saturated steam can
come into contact with all surfaces of the goods during the sterilizing phase.
Homogeneous instruments require only the surface of the instrument to be sterilized. Instruments with holes in them have both inner and outer surfaces and the inner surfaces
are difficult to access with steam. It is also easy for air to remain entrapped in larger textiles. Another problem is sterilization of items which are sensitive to heat and moisture.
Facts and features about steam sterilization (continued)
Extreme engineering
Tremendous forces affect the load during the sterilization phase. It takes 3 liters of water to sterilize a package comprising 7.5 kilograms of textile in a steam sterilizer with a
63-liter chamber volume, running a complete textile program. The energy released from
the steam generated by the 3 liters of water when condensing on/in the load (changing
phase from steam back to water) will be 3 x 2 250 kJ = 7 750 kJ. This is an enormous
amount of energy, equivalent with the force needed to lift two jumbo jets 1 meter above
the ground.
During the sterilization phase, the pressure within the chamber is increased up to slightly
over 3000 bar, corresponding to a pressure on the back (inside) of the door of the sterilizer chamber in a small table-top sterilizer equivalent to 2 (two) metric tons. The size of
the door is approximately 6 dm3 (75 sq. in.). In a larger hospital steam sterilizer (63-liter
chamber volume), the corresponding pressure on the inside of the door will be 10 (ten)
metric tons!
The sterilizer adds the wrapping
In the sterilization process, the microbial molecules will be destroyed (broken
down to minor units) but the residuals will still be there. They can only be washed away! It cannot be stressed enough that the sterilization procedure adds the
wrapping, and also gives a bigger safety margin!
Dangerous and entrapped air-pockets
In the sterilizer, for energy to be released and to ensure that all items intended to be sterilized are accessible to the saturated steam, it is important that the air first be removed
from the sterilizer chamber and from all parts of the goods intended to be sterilized.
Instruments and items located where there are pockets of air never come in contact with
saturated steam and will therefore not be sterilized. The same goes for internal surfaces
in hollow instruments, where air-pockets can easily be entrapped.
Steam sterilization with pre- and post-vacuum phases – safe and reliable
In steam sterilizers with pre- and post-vacuum processes, the sterilization process consists of three main phases: pre-treatment, sterilizing and post-treatment.
During pre-treatment, the air is expelled by pulses of vacuum and the introduction of
steam. The temperature increases gradually, up to the degree at which sterilization is to
take place.
Perfect steam within very narrow temperature range
The key prerequisite for saturated steam – and to achieve the relatively large release of
energy – is that the water is at the boiling point, where a change of phase (saturated
steam to water) can occur. The boiling point of a liquid is reached when the vaporization
pressure of the liquid exceeds the surrounding air pressure. At normal air pressure (760
mm Hg – 1 atmospheric pressure at sea level), this occurs at +100°C. The boiling point
varies according to air pressure and therefore under conditions of low or high pressure.
Superheated or supermoist steam will not work
The presence of supersaturated supermoist steam results in the failure of steam to penetrate the items in the chamber. Too much air can be compared to an attempt to force
the air out of the leg of a pair of jeans: it is easy if the textile is dry, but if it is wet much
more force is necessary to expel the air. The same phenomenon occurs with packages or
porous items in supermoist steam.
If the temperature in the steam sterilizer is too high, the steam will be overheated. Overheated steam has a temperature exceeding the boiling point and in this case an energy
conversion phase will not occur and the energy of the overheated steam will be spent in
heating up the instruments. The sterilizer will thus resemble more a hot-air oven, requiring
much higher temperatures and longer exposure to achieve sterility of the goods.
Facts and features about steam sterilization (continued)
“Visible steam” is not steam
When water boils, the saturated steam nearest the surface of the boiling water is invisible
to the naked eye. The visible “foggy steam” at a distance of a few centimeters from
the surface of the boiling water is actually not saturated steam. When steam can be
discerned as fog it has already started to condense as it gets into contact with the cooler
surrounding air. What can be seen is supersaturated or supermoist steam and it is the
microscopically condensed liquid particles which make the “steam” visible. If you put your
hand in this “visible steam” it will become warm and quickly moist from the condensation.
However, if you put your hand into the invisible saturated steam, you will rapidy burn
yourself due to the great release of energy from the saturated steam.
A cloud of condensed water (mist) coming
out of the chamber of the sterilizer on opening
the door after the completed sterilizing cycle,
indicates that the steam intended for sterilization
has been too wet.
This is usually due to overloading the
sterilizer or trying to run the wrong load in
the wrong program.
If the steam is too wet it is actually NOT
steam but condensed water - and there is NO
possibility for the release of the energy when
water changes from gas to fluid phase. The
energy release needed for sterilization will NOT
be there. Consequently the load cannot be
Residual moisture must be minimized
Residual moisture in the packaging material after sterilization will acts as a potential
pathway for microorganisms to penetrate the package. The most common fault is that
the chamber has been packed too tightly or that the load is too heavy.
.
Post vacuum is an effective method for drying the load and removing remaining
moisture.
Different methods of sterilization - advantages and disadvantages
Gravity displacement autoclaves – not for sterile articles
This is the simplest type of steam sterilizers. The standard method for air removal is based
on steam being lighter than air; when steam is introduced in the autoclave chamber it
forms a stratified layer across the top internal volume in the autoclave chamber. With
increased volumes of steam introduced, the steam will press (force) the air towards the
bottom of the autoclave chamber.
In the bottom of the autoclave chamber (at the floor), a valve opens and lets the air out
when steam is forced into the chamber – downward displacement.
There are a number of important drawbacks with gravity-displacement autoclaves:
As the steam is introduced into the chamber, the air pushed downwards by the steam
wave front can diffuse into the steam. Therefore the steam has to be constantly and rapidly
renewed. Even if microscopic, the remaining air-pockets will prevent the steam from getting
in contact with the items to be sterilized. And no contact means no condensation, no
energy-release and consequently no sterilization in these areas. This is the major reason
why such autoclave cycles can only be used for sterilization of solid and unwrapped
articles.
Introducing steam with great speed into the chamber can cause other disadvantages.
High-velocity steam carries with it microscopically small water particles – atomized
particulate water droplets. This results in moist steam, which is not able to release as
much energy as saturated steam.
An additional problem with high-velocity steam is that the introduction causes turbulence
in the autoclave chamber, thereby increasing the mix of air into the steam.
Downward- (gravity-) displacement sterilizers are widely used. However, these are
increasingly being superseded by steam sterilizers with pre- and post-vacuum processes.
Preconditioning with several pre-vacuum phases is essential for sterilization of wrapped,
hollow or porous items.
Flash steam sterilization – only in case of emergency
Flash steam sterilization is a process for steam sterilization of items for immediate use and
should be used only in carefully selected clinical situations. Flash steam sterilization can
be described as downward gravity displacement sterilization using a continuous flow of
high-velocity steam throughout the sterilization phase.
Flash steam sterilization should be used only for solid, unwrapped items. Items must be
transported immediately to the point of use so that sterility is maintained.
All kinds of downward gravity-displacement sterilization are processes
for steam sterilization of items for immediate use and should be used
only in carefully selected clinical situations.
Downward gravity-displacement autoclaves can be regarded as a
method for disinfection
Facts and features about steam sterilization (continued)
Energy transfer is the basis for all types of sterilization. In steam sterilization, the death of
the microbes is caused by very large amounts of energy in the form of heat attacking the
microorganisms when steam condenses – turns from steam (the gas form of H2O) into
water (the liquid form).
Steam sterilization can be compared with the boiling of food. During boiling, carbohydrates
and proteins break down, the food becomes softer – both more chewable and also easier
for the human digestive system to absorb.
Without functional proteins and carbohydrates, a microbe cannot maintain its own
metabolism and function during steam sterilization and will therefore die.
Gravity-displacement autoclaves are the simplest type of steam sterilizers. The standard
method for air removal is based on steam being lighter than air. The whole sterilization
process comprises three (3) phases: preheating of the load, holding time (i.e. when the
actual sterilization takes place) and post-treatment to cool down the load and for removal
of residual water.
Downward gravity-displacement sterilization always results in residual air in
the autoclave chamber and should therefore only be used for solid, unwrapped
items).
Items must be sterilized at the point of use for immediate re-use, so that sterility
is maintained. Items must not be wrapped and must not be transported or
stored.
A steam sterilization cycle at +121°C (+250°F) for 15 minutes will inactivate most heatresistant microbes. However, increasing the temperature to +134°C (+273°F) is preferable,
since this offers a much larger safety margin.
Different methods of sterilization - advantages and disadvantages (continued)
Steam sterilization with pre- and post-vacuum phases
In steam sterilizers with pre- and post-vacuum processes, the sterilization process
comprises three main phases: pretreatment, sterilizing and post-treatment.
During pretreatment the air is expelled by a number of pulses of vacuum and the
introduction of steam. The temperature increases successively, up to the degree at which
sterilization is to take place.
In the pre-vacuum phases, each vacuum pulse brings the air pressure in the sterilizer
chamber down below 300 mbar, the same air pressure as on the top of Mount Everest.
Some steam sterilizers go as deep as 100 mbar in the pre-vacuum phases, which is the
same air pressure as at 20,000 – 25,000 meters (65,000 – 82,000 feet) above sea-level,
i.e. far above the maximum altitude of most aircraft.
Virtually all air must be evacuated during pretreatment (pre-vacuum phase) so that the
saturated steam can affect the goods during the sterilizing phase. If present, trapped air
pockets in the goods prevent steam penetration during sterilization of porous material such
as textiles and hollow items. Solid instruments require only the surface of the instrument
to be sterilized. Hollow instruments with cavities and/or tubules have both inner and outer
surfaces and the inner surfaces are difficult to access with steam. It is also easy for air to
remain entrapped in larger textiles.
The number of evacuation phases necessary is highly dependent on the degree of vacuum
in relation to the number of vacuum pulses. A single vacuum pulse is insufficient and
inadequate for wrapped/hollow/porous loads. Steam sterilization of hollow instruments
and porous objects always requires at least three (3) pre-vacuum pulses. Steam sterilization
of objects with long, narrow lumina, requires several pre-vacuum pulses to a defined, preset, vacuum level.
The actual sterilization period, called the holding time, starts when the temperature in all
parts of the sterilizer chamber and its contents (the load) have reached the sterilization
temperature. The temperature should then remain constant, within the specified
temperature band (134°C±2°C), throughout the sterilization phase (plateau/holding
time).
The pressure / vacuum, in itself, has no lethal effect on the microorganisms. There
are experiments where common bacteria have been able to keep alive under extreme
pressures of up to 400 atm. The killing effect is due to the energy transferal when the
saturated steam condenses on the items to be sterilized and thereby causes cleavage of
intramolecular hydrogen bonds between proteins.
In the post-treatment phase, either the steam or the revaporized condensed water is
removed by vacuum to assure that the goods dry rapidly.
Wrapping makes the load porous – requires vacuum-process
It is important to note that packaging material itself (paper, textiles) is
a porous load and should be handled as such. All packaged/wrapped
goods require sterilizing in steam-sterilizer processes with pre- and
post-vacuum cycles.
Facts and features about steam sterilization (continued)
In steam sterilizers with pre- and post-vacuum processes (i.e. B-cycle), the sterilization
process consists of three main phases: pretreatment, sterilizing and post-treatment.
During pretreatment, the air is expelled by a number of pulses of vacuum and the
introduction of steam. Virtually all air must be evacuated during pretreatment (pre-vacuum
phase) so that the saturated steam can affect the goods during the sterilizing phase
If present, trapped air pockets in the goods prevent steam penetration during
sterilization.
A single vacuum pulse is inadequate for wrapped/hollow/porous loads. Steam
sterilization requires at least three (3) pre-vacuum pulses.
If not dry, it is not sterile and safe!
In the post-treatment phase, either the steam or the revaporized condensed
water is removed by vacuum to assure that the goods will dry rapidly.
The boiling temperature (the temperature where water evaporates) can be elevated by
increasing the pressure. This phenomenon also works the other way around; by lowering
the pressure the boiling temperature will decrease. This is what is used in the postvacuum phase of the sterilizing cycle.
Directly after the completed plateau-phase, all the items in the sterilizer load have a
temperature of +134°C (+273°F), heated up through the condensation of the saturated
steam. At this moment, the load is also moist from the condensation. The sudden change
to a deep vacuum will rapidly lower the boiling temperature to around +35°C (+95°F). With
all the heat still accumulated in the load, the residual water will immediately evaporate,
leaving a dry load.
Different methods of sterilization - advantages and disadvantages (continued)
Dry-heat sterilization – oxidation of items
Dry heat can be used to sterilize items that might be damaged by moist heat. One advantage is
the relatively low cost of equipment, but the disadvantages are the duration of the process and the
high temperature. Diffusion and penetration of heat are slow because the heat transfer medium
is poor, and there is a lack of available heat, particularly compared to steam. Long exposure
times are required because the killing rate by dry heat is slow, as is heat absorption. Killing by
dry heat is an oxidation process and both the oxidation and the high temperatures required may
damage the materials to be sterilized. Certain alloys can be softened by exposure to such high
temperatures.
Since heating in a dry-heat sterilizer is slow, overloading of the dry-heat sterilizer can delay heat
convection. This can be caused either by preventing circulation or by heat absorption in the goods.
Consequently in an overloaded dry-heat sterilizer there is a risk for uneven heat distribution. A heavy
load of instruments will then require an extremely long process time. Under such circumstances,
organic material will tend to char and bake on the items to be sterilized.
For the sterilization of medical devices there has been almost no new development or improvement,
and dry-heat sterilization is about the same as it has been for several decades.
Unsaturated chemical vapor sterilization – not a low-temperature process
In several countries, unsaturated chemical vapor sterilization in worktop sterilizers is still common.
Even though the procedure is based on the use of formaldehyde solution (formalin),
unsaturated chemical vapor sterilization should not be confused with low-temperature
sterilization.
Unsaturated chemical vapor sterilization involves heating a chemical solution containing
formaldehyde, ethanol, acetone, ketone, water and other alcohols in a closed chamber. Usually
a solution of primarily ethanol with added water and a low percentage of formaldehyde (0.23%)
is used.
The temperature during the sterilization phase varies between different brands but is usually around
+130°C (+270°F), but there are also programs with lower temperatures. The steam pressure
during the holding time (sterilization phase) is 1 380 bar – 2 750 bar (20 – 40 psi).
Unsaturated chemical vapor sterilization of carbon steel instruments (e.g. dental burs) causes
less corrosion than steam sterilization because of the low level of water present during the cycle.
Instruments should be dry before sterilizing.
Although this procedure is less corrosive to sensitive instruments than steam sterilization, it has
disadvantages. Formaldehyde has an extremely piercing smell even in low concentration.
After the process, all residuals of formaldehyde must be removed, which requires special separators
and air-filters of exhausted vapor from the chamber.
Authorities should be consulted for hazardous waste disposal requirements for this sterilizing
solution.
Unsaturated chemical vapor sterilization functions in accordance with the same principles as
downward gravity displacement sterilization and should be used as such. There are reports of
poor penetration of hollow items, e.g. rotary dental instruments (hand pieces, turbines).
Again: Unsaturated chemical vapor worktop sterilizers are NOT the same as
low-temperature sterilization using formaldehyde (see below)..
Facts and features about steam sterilization (continued)
Careful loading
Another factor which influences the result of the sterilizing procedure is the way in which
the chamber is loaded.
The goods should not be tightly packed: the steam must be allowed to penetrate
all parts of the goods.
Whether the residual water can be removed or not during the post-sterilization phase
depends on several factors. If the condensate is collected where it is in contact with metal
surfaces or absorbed in a textile surrounding an instrument, practically all condensate will
evaporate, resulting in a dry load.
Residual moisture must be minimized
Residual moisture in the packaging material after sterilization will acts as a potential
pathway for microorganisms to penetrate the package. The most common fault is that
the chamber has been packed too tightly or that the load is too heavy.
If solidly packed instruments are to be sterilized, the total weight of the load must not
increase by more than 0.2% after sterilizing, because of residual moisture in the load
(packaging material) For sterilizing of textiles, the total weight of the load must not increase
by more than 1% after sterilizing.
Post vacuum is an effective method for drying the load and removing remaining
moisture.
Steam sterilizers add the possibility of packaging the goods. Today’s demands
on sterile goods are that the goods are to be sterile the very moment they are to
be used. This means they must be packaged in special, close-fitting packages
that allow nothing to penetrate. This is why modern steam sterilizers must
include pre- as well as post-vacuum treatment.
It is important to note that packaging material itself is a porous load (paper,
textiles) and should be handled as such. All packaged/wrapped goods require
sterilizing in steam-sterilizer processes with pre- and post-vacuum cycles.v
Sterile wrapping (packaging) is also a prerequisite if sterile goods are to be
transported and stored at different locations.
Low temperature sterilization – a delicate process
Sterilization with ethylene oxide gas (ETO) - a lethal process
Ethylene oxide gas (ETO) has been used extensively in many large healthcare facilities
as a low-temperature sterilant. Its primary advantage is that it can sterilize heat- and
moisture-sensitive items without deleterious effects.
Extended sterilization times of 10-48 hours, depending on the materials, and stringent
standards for ETO emission make it an impractical method in healthcare settings. ETO
gas flow has poor penetration through hollow instruments with small lumina.
The vapors of ETO gas are flammable and explosive, although the fire hazard can be
reduced by diluting ETO with carbon dioxide or fluorocarbon. The gas is heavier than air
and can travel long distances to a source of ignition and flash back to a leaking or open
container
Since the 1980s, ETO gas has been classified as both a mutagen and carcinogen, and
its use is now strictly regulated.
ETO has a sweet odor with an odor threshold of 200 ppm (perception) but is not
distinguishable from other organics until 500-700 ppm. The IDLH (Immediately Dangerous
to Life and Health) level for ETO is 800 ppm.
Formaldehydes sterilization at low temperature
Formaldehyde is a colorless, toxic gas. The boiling (vaporization) temperature is
-21°C (-6°F). Formaldehyde is highly soluble in water and commercially available as a
35% solution called formalin.
In the low-temperature sterilization process, the pure heat energy of steam sterilization
is replaced by a mixture of steam and formaldehyde gas at temperatures in the range of
+55 to +80°C (+122 to +176° F).
The presence of steam allows the formaldehyde to penetrate and kill any
microorganisms.
Before the formaldehyde is admitted, the goods are subjected to pre-treatment consisting
of repeated evacuations and steam flushes. This very important procedure aims at
removing air from the goods and the chamber, while simultaneously humidifying the
microorganisms to make them susceptible to formaldehyde. The effectiveness of the
humidifying part of the pre-treatment is essential for the rest of the process.
A formalin solution is injected from a sealed bottle. The
formalin is then evaporated and enters the chamber as a
gas. A vacuum in the chamber assists the admission of
the gas. Steam is then added to keep the temperature
at the predetermined level. The admission is repeated
several times to enhance the penetration into long, narrow
lumens and cavities.
During the sterilization time, a 35 % formalin solution,
which is evaporated before entering the chamber,
sterilizes the load. The chamber is maintained at the
specified temperature, sterilant concentration, pressure
and humidity.
Facts and features about steam sterilization (continued)
Endospores hiding in salt crystals
The result of a sterilization process is greatly influenced by the quality of the steam and
the water quality influences the quality of the steam produced. Certain standards are
therefore required for the quality of the steam as well as the water being used. Solid
particles such as welding parts, graphite, rust flakes, sand etc. must not be present. Nor
can other liquids than the water itself or chemicals be present. The salt content should
not exceed 1 mg/kg steam.
The ion concentration and pH-level will affect the sterilization results. For example, a
single calcium carbonate crystal can harbor up to 100 viable bacterial endospores.
Spores can have a 900-fold increase in resistance to steam when occluded in calcium
carbonate crystals. Therefore deionized and clean water should always be used for steam
sterilization.
Salt cristalls on instrument surfaces seen through electronmicroscope
Checking the so-called conductivity of the water gives a measurement of the salt (ion)
content. The conductivity is the capability to transfer electricity which in turn is dependent
on the amount of ions in the water. Higher levels of ions (salts) in the water will result in
higher conductivity.
The conductivity is also related the risk of corrosion of instruments, e.g. rust, calcification,
mineral deposits, discolorations etc
With respect to purity, in the condensate from the steam, the
following values should not be exceeded:
Chemical substance
concentration in mg/kg
SiO2
0.01
Iron
0.1
Cadmium
0.005
Lead
0.05
Other heavy metals
0.1
Chloride
0.1
Phosphate
0.1
Other properties
Conductivity
< 3 µS/cm (at 20ºC)
pH-value
5–7
Hardness
< 0,1 dH
Low-temperature sterilization – a delicate process (continued)
After the predetermined sterilizing exposure time, the formaldehyde is effectively removed
from the goods by repeated vacuum and intermediate steam flushes.
The post-treatment process ends with a deep vacuum, followed by a huge number of
pulsating air flushes via the air admission filter. This part of the process removes residual
formaldehyde in the goods and the chamber.
The use of formaldehyde may only be undertaken by fully trained personnel. Formaldehyde
should be disposed of as hazardous waste. Personnel should wear appropriate protective
equipment to protect skin and eyes from contact with the solution and avoid vapor
inhalation. Adequate room ventilation is necessary.
There is a separate European Norm for formaldehyde low-temperature sterilizers,
EN14180.
Plasma sterilization – combination of three killing actions
To use of so called plasma to achieve sterilization is a possible alternative to conventional
sterilization for heat sensitive instruments.
The gas plasma process uses ionized gas which will give a combined action of ultraviolet
light radiation and the action of free radicals. Ultraviolet light is a method for transferring
energy through irradiation. Free radicals are molecules with an uneven number of electrons,
for example the hydroxylradical molecule (HO, hydrogen and oxygen). Since the molecule
is missing one electron it is highly reactive. Another example is oxygen radicals (O). Radicals
are extremely reactive chemical components, and have lethal effects on microbes.
The initial sterilization phase consists of removing the air from the sterilizer chamber as well
as air entrapped in the items to be sterilized. Gas is then introduced into the chamber. The
gas is exposed to a very high energy field, transforming the gas into a low-temperature
gas plasma.
When the gas molecules stabilize after the removal of the high energy field, they strive
to return to normal conditions. To do so, the gas molecules (plasma) have to release the
added energy , which is done by emission of ultraviolet light radiation.
In commercially available plasma sterilizers, vapor of hydrogen peroxide or vapor of
peracetic acid is used as gas. This gives triple-phase sterilization: from the substance
itself; by exposure to free radicals; and through irradiation from ultraviolet light.
Facts and features about steam sterilization (continued)
The result of all steps included in the reprocessing of instruments from usage through
transport, decontamination, cleaning, disinfection, wrapping, sterilization, storage and
delivery is greatly influenced by the handling itself.
Proper instrument handling directly influences the lifespan of the
instruments and also to a great extent the quality as well as the final result
of treatments carried out with these instruments.
To ensure proper and complete elimination of all biological materials prior to sterilization,
it is crucial to control and handle the whole process of decontamination – cleaning and
disinfection – correctly.
The cleaning of instruments and articles is the all-important issue in decontamination,
disinfection and sterilizing. It is not only the microorganisms (i.e. bacteria, virus, fungi etc)
that have to be removed during the cleaning process, but also organic substances. These
substances consist of carbohydrates, fat and protein and if they are not removed from
the instruments before sterilization, the sterilization process itself will prove inefficient.
What the steam sterilizer really adds is the possibility of packaging the goods. The
demands on sterile goods are that they must be sterile the very moment they are to be
used, and they must therefore be packaged in special, close-fitting packages that allow
nothing to penetrate them. All packaged/wrapped goods require sterilizing in steamsterilizer processes with pre- and post-vacuum cycles.
Residual moisture in the packaging material after sterilization acts as a potential pathway
for microorganisms to penetrate the package. The most common fault is that the chamber
has been packed too tightly or that the load is too heavy.
Steam sterilization requires:
• evacuation of as much remaining air as possible from the sterilizer
chamber;
• the sterilizer chamber to be filled with saturated water vapor;
• the correct pressure and temperature in the sterilizer chamber to
achieve saturated water vapor;
• the sterilizer to be correctly packed, with the correct load of goods;
• instruments and articles being super-clean before sterilization.
Low temperature sterilization – a delicate process (continued)
Plasma sterilizers work at low temperatures: +46 – +50°C (+115 – +120° F).
An important shortcoming of plasma sterilization is its dependence on the actual thickness
of the microorganisms to be inactivated, since any material covering the microorganisms,
including packaging, will slow down the process.
The penetration of the ultraviolet light is also restricted by any organic materials (e.g. cell
debris) covering the spores, and by the stacking or aggregation of spores.
The advantages of gas plasma sterilization are that it is a fast, low-temperature process. It
is reported to be suitable for the sterilization of metals, natural rubber, silicone and various
polymers such as polyvinyl chloride.
It is not suitable for the sterilization of liquids, oils, powders, biological tissues, paper,
cotton and linen (note: wrapping materials!).
It has inferior penetrability compared with other methods. The Center for Disease Control
and Prevention (CDC), USA, does not recommend gas plasma sterilization of endoscopes
with lengths > 40 cm or an internal lumen diameter < 3mm.
Gas plasma sterilization processes use strongly oxidative chemical sterilizing agents
(hydrogen peroxide or peracetic acid), and it is well known that these agents can cause
surface oxidation, including surface oxidation of some biomedical elastomers.
Hygiene and infection control must be considered as today’s most important
tasks in all healthcare systems, and must be integrated in all activities.
Facts and features about quality processes
Corrosion destroys delicate and sophisticated instruments
Corrosion is a common problem. When in the same fluid, instruments and other articles
made of different metals may corrode, and corrosion destroys sharp and delicate
instruments. Corrosion pits also make the surface rough, which increases the possibilities
of microorganisms to attach themselves to the instruments. Mixing different types of metal
in a liquid solution results in an electrochemical cell and causes corrosion. This is often the
case during cleaning, ultrasonic baths and washer-disinfectors.
Chlorines
Stainless steel is extremely resistant to many chemical substances. Among the few
substances that can destroy stainless steel are halogen salts, the most commonly used
and harmful being chlorides.
Depending on the concentration of chlorides, the corrosion damage can range from small
points of attack (so-called “pitting corrosion”) to completely damaged instruments with
large corrosion holes.
Important chloride sources to pay attention to during instrument usage and processing
are: fresh-water chloride content, insufficient demineralization of water used in washerdisinfectors and for steam sterilization, leakage or spillage from ion exchangers used for
water softening, drug residues (physiological salt solutions), organic residues (body fluids
such as blood, saliva, sweat etc), laundry, textiles, packaging materials and the use of
agents not suitable for or improperly used in the treatment of surgical instruments.
If paper wrapping consists of chlorine-bleached paper, residual chlorine ions can be
released from the paper when in the wet stage (for instance in the steam sterilizer) and
indirectly harm instrument surfaces. The same phenomenon can appear with textiles and
textile products if chlorine has been used in the manufacturing process or during laundry.
Chlorines are commonly used for bleaching textiles.
Textiles must not have any detergent residue and should be neutral (pH7) if immersed in
water or steam. The residue of high alkaline detergents (pH 9-13) used by laundries to
clean towels and other textiles may cause stains on instruments.
This is also one of the reasons why instruments normally should not be dried with towels
– preferably naked instruments and articles should be touched and handled as little as
possible before wrapping and sterilization.
Corrosion of instruments due to extended contact with sodium hypochlorite
Quality assurance achieves the best possible result
Quality programs add many benefits
Quality assurance and quality processes have several implications, one of which is of
course to give the patient the best possible care with as few side-effects as possible, all
with the very best safety and comfort, and at a reasonable price.
Proper instrument handling directly influences the lifespan of the instruments and, to a great
extent, the quality and final results of treatments carried out with these instruments.
Validation and process control of all medical devices used to reprocess the instruments
– such as ultrasonic baths, washer disinfectors and sterilizers – is also of consequence.
The result of all steps included in the reprocessing of instruments, from usage through
transport, decontamination, cleaning, disinfection, wrapping, sterilization, storage and
delivery, is greatly influenced both by the handling itself and by the different media used
during reprocessing (water, steam, detergents, chemicals, etc). For example, a sterilization
process is to a high extent influenced by the quality of the steam, which in turn is influenced
by the quality of the water used to produce that steam. Certain quality standards are
therefore required for the steam as well as the water.
High demands on manufacturers of instruments
Design and production of medical devices include knowledge about the intended purpose
and use. This must cover the whole cycle from ease of handling and ergonomic demands
to the choice of material. For surgical instruments, requirements in terms of elasticity,
strength, rigidity properties, as well as resistance to wear and corrosion, must be taken
into account.
Instruments made of high-quality stainless steel with high elasticity and high tensile
strength are normally highly resistant to wear and corrosion. All of these capacities can be
negatively influenced by improper handling of the instruments, particularly in connection
with cleaning, disinfection and sterilization.
Instruments made of stainless steel are often believed to be extremely strong and suitable
for using for almost any amount of time. But the truth is that all kinds of instruments
can be harmed both by mechanical, thermal and chemical influences. Instruments often
consist of different parts and of different kinds of metals and alloys, even in the same
instrument.
Facts and features about quality processes (continued)
Dissolved minerals in water
The quality of water used in the processing of instruments has considerable influence on the result after
handling. Natural water contains dissolved salts, minerals and ions.
A washer-disinfector works with water temperatures close to the boiling point and a steam sterilizer uses
the principle of condensing and evaporating water. Therefore if the water used in these processes contains
too high a concentration of ions, there will be a concentration of ions on instruments when water in the
specific processes evaporates from the instruments.
The most common form of scaling from water is calcium carbonate (CaCO3), also known as lime. Scaling
leaves deposits on instruments and articles, and most scaling is hard and very difficult to clean. It is possible
for corrosion to occur underneath such deposits. With increased water hardness, blood removal also tends
to become more difficult.
Lime and other deposits can also enclose microorganisms and biological residues. A single calcium
carbonate crystal can harbor up to 100 viable bacterial endospores. Spores can have a 900-fold increase
in resistance to steam when occluded in calcium carbonate crystals.
Enclosed microorganisms can of course cause infections in surgical wounds; lime and other scale particles
being insoluble and coming loose from instruments during surgery can cause granulomas.
If water contains sodium carbonate (Na2CO3), the sodium carbonate will hydrolyze when the water is
boiling, thereby producing free alkali that causes caustic embrittlement and destruction of instruments.
Stain or plating – what is the difference
Stains can either be plated or deposited on the surface of an instrument. Stains are discolorations of metal
by material added to the surface of the metal. Plating means that material is deposited on the surface
of instruments by chemical action. Instruments of different metals in a chemical bath may be subject to
plating. An aqueous chemical solution might serve as an electrolyte, making it possible for metal ions to
move from one instrument to another.
Plating changes the surface structure on the instruments, which can make the instrument in question more
prone to corrosion
Plating due to prolonged contact with acidic
disinfectant.
Staining due to close contact with other rusty
instruments.
Body fluids to be removed as soon as possible
Blood, pus, and other secretions contain chloride ions that cause corrosion, most often
appearing as an orange-brown color. If left on the instruments for any extended period
of time (up to 4 hours), the instrument will be marked and stained, especially if these
residues are allowed to dry. If the dried-on debris is “baked-on” during the sterilization
process, the result will be even more devastating, with additional concentration of ions
and extreme difficulty to remove.
Careful instrument processing necessary to maintain high quality
Careful handling is important to maintain the tenability of instruments. They should not
be thrown or dropped, but should be processed in trays, holders or stands to prevent
impact against each other. Contact with each other should be minimized during washing,
disinfection and sterilization. The instruments must be arranged in such a way as to
prevent mechanical damage through contact.
Arrange safe transport routines
Closed systems should be used to transport contaminated medical devices from the
operating area and wards to the decontamination and sterilizing area. Dry disposal
is preferred. If wet disposal is used, instruments should be immersed in a detergentdisinfectant solution that has no protein-fixing effect.
Because of the corrosion risks, instruments should be processed for reuse not later than
6 hours after use.
Closed systems should also be used when transporting sterile medical devices from the
sterilizing area out to different users within the healthcare setting. Everybody involved
should be able to trust that all quality procedures in use will assure the highest possible
safety of sterile articles.
Proper design of the sterilizing area itself will add quality; the whole area should be ”oneway-only”. This is best achieved by designing the area so that there is only one possible
direction in which to transport instruments from decontamination through cleaning and
disinfection to wrapping and sterilization and finally to storage facilities.
Facts and features about quality processes (continued)
Deionized water must also be clean
Stains are often mistaken for rust (which is a chemical change in the metal material) because of the similar
brown/orange color that stains usually have. Brown/orange-colored stains are usually phosphate deposits
on the instrument. Phosphate can come from traces of minerals in the sterilizer water source, a dirty
sterilizer, high alkaline or acidic detergents, surgical wrappings, and dried blood or tissue. Condensation of
steam on the instruments during steam sterilization can deposit the phosphate and produce the stain on
the instrument surface. Iron, copper or manganese can cause similar discoloration.
Steam sterilizers designed not to recycle water during sterilization are the optimal solution. In steam sterilizers
equipped with an internal water tank for reuse of water, cleaning of the water tank as well as regular (daily)
exchange of water is necessary to maintain high quality.
A brown/orange stain or a blue-black stain can occur from plating during the cleaning or steam sterilizing
process. Through electrolysis, when dissimilar metals touch each other while being sterilized, ultrasonically
cleaned, or sometimes even stored together, the stained material actually bonds the stain material to the
instrument metal.
Cold sterilization can cause corrosion
Most cold sterilization solutions render instruments sterile only after a very long exposure time (more than
10 hours’ immersion, usually overnight). This prolonged chemical action can be more detrimental to the
surgical instruments than a much shorter steam sterilization cycle.
In one study, when comparing the efficacy of 2% glutaraldehyde with 0.2% peracetic acid, when organic
matter was added, the 0.2% peracetic acid formulation cleaned without corrosion, while 2% glutaraldehyde
fixed the matter to the scalpel, causing corrosion within 2 hours.
Never use abrasives
Neither stains nor plating should be removed using abrasive
brushes or other substances, since this will only destroy delicately
polished instruments and also remove the important passive layer
on stainless steel. If needed, instruments should be refurbished
at surgical instrument service facilities by professional technicians
recommended by the manufacturer.
Cleaning of difficult areas
The hinged areas of scissors and other instruments should be kept clean
and clear of tissue and other matter. Over time, the small area in and
around the hinge can build up a hardened layer of material, resulting in
corrosion. Once this build-up begins, the effectiveness of the instrument
is quickly reduced.
Maintenance of such instruments should include application of instrument
milk to joints, hinges, locks and friction surfaces. These agents should
be based on paraffin/white oil, be biocompatible, suitable for steam
sterilization and vapor-permeable. Silicon oils should never be used.
Replace instruments that can not be properly cleaned
IInstruments with coagulating residues that cannot be removed even by intensive cleaning must be
discarded, because their proper function and required hygienic condition can no longer be guaranteed.
Instruments with cracks in joint areas as well as those that are damaged, distorted or otherwise worn must
also be replaced
.
Water quality will affects the quality of the whole sterilization
process
Hard or soft water – both alternatives will add costs
The result of a sterilization process is greatly influenced by the quality of the water being
used during the entire process.
Soft water has a lower ion content and hard water higher. Hardness is measured in °dH
(= “German degrees of water hardness). Soft water has a relative hardness below 5°dH
and hard water over 10°dH.
Harder water requires additional concentration of detergents for cleaning, while soft water
increases the risk of corrosion.
The use of more detergents to compensate for hard water might be more expensive
than to install proper water deionizing equipment. On the other side of the scale, the
increased risk for corrosion due to soft water might cost much more in investments in
new instruments than the costs for using deionized water.
Calcium and magnesium have a buffering capacity, but in higher concentrations this also
leads to decomposition in the form of lime deposits and scaling.
Replacement of ions does not improve the final result
One way to soften water is by using sodium salts to replace the hardening ions, but this
does not reduce the total load of ions in the water, it merely alters the molecules present
in the water. Sodium salts react with the calcium and magnesium in the water forming
other types of salts which in themselves can cause depositions on the materials and
instruments.
Ion exchangers not suitable in health care settings
Other ways to deionize water are so-called ion exchangers, using silicic acids (Si(OH)4),
which can cause glaze-like discolorations of instruments. This cannot be controlled
through conductivity analysis of the water in use. The best method is to use fully distilled
deionized water or water deionized by effective filtration through chemically active filters
in several steps.
There are many methods to clean water and remove undesirable components; the
very best is the usage of deionized water. Deionized water also has an active effect on
microorganisms and biofilms through so-called reverse osmosis.
Detergents can become corrosive in the wrong environment
Calcium and magnesium ions in hard water react with the higher fatty acids of soap and
detergents to form an insoluble gelatinous curd. This curd contains a concentration of
chemicals from the soap/detergent, and the gelatinous curd is itself corrosive.
Residuals must be removed by rinsing
Thorough rinsing after the cleaning process is important since residuals of detergents
left on the instruments can become concentrated due to heating during the subsequent
sterilization phase – even if the pH-level of the detergent is adequate, it can reach critical
levels if allowed to concentrate in droplets on instruments and other surfaces.
Facts and features about quality processes (continued)
Avoid acidic and high-alkaline detergents
Black stains are usually due to an acid reaction. An acidic detergent deposit left on the
instrument during sterilizing might cause a black stain. Strong substances, containing
acid or alkaline-based solutions can lead to pitting and staining.
Instruments should be cleaned with appropriate low-alkaline detergents. Ordinary soap,
laundry soap, or surgeon’s hand scrub are intended for other purposes and will damage
delicate and sensitive surgical instruments.
Wash or rinse off directly after use
The washing process should begin within 10 minutes after surgery, even if sterilization
will take place much later. Washing instruments within a few minutes of surgery is your
best defense against corrosion, pitting, and staining.
Instruments that can be taken apart must be disassembled in accordance with the
manufacturer’s instructions prior to cleaning. A 3% hydrogen peroxide solution will remove coagulating residues adhering to instruments after usage.
Soft plastic brushes, lint-free cloths or cleaning guns are recommended for cleaning.
Never, however, immerse stainless steel instruments in physiological salt (NaCl) solution.
Prolonged instrument contact with sodium chloride solution leads to pitting and stresscorrosion cracking.
Unsafe use of dry-heat sterilizers
Multi-colored stains or chromium oxide stains result from excessive heat. These rainbow
colored stains indicate the instrument may have lost some of its original hardness after
being heated. Cutting edges lose their sharpness quickly when hardness is reduced. Flash
flame decontamination (an instrument is decontaminated by inserting it into a flame for
a few seconds) changes the molecular structure of most materials adversely, shortening
the useful life of instruments.
In dry-heat sterilizers, the temperature can reach very high peaks because of variations in
the heating-up procedure itself. There is also a risk of extreme overheating in minor zones
in the dry-heat sterilizer, for example close to or the area of the chamber in contact with
the heating elements. This super-heating in dry-heat sterilizers has adverse effects on
costly instruments.
Three different kinds of stainless steel for various purposes
There are three major groups of stainless steels: austenitic, ferritic, and martensitic.
For surgical instruments, martensitic steels are most common. Martensitic steel contains
11.5-18% chromium and up to 1.2% carbon, with nickel sometimes added. They can be
hardened by heat treatment and have modest corrosion resistance.
Hard or corrosion-prone surface depends on the amount of carbon
Stainless steel resists rust, can be ground to a fine point or edge, and retains its sharpness.
During manufacturing, the carbon content can be altered to improve desired qualities.
Increasing the amount of carbon makes the stainless steel harder, resulting in for example
a harder cutting edge on a pair of scissors. However, at the same time the higher carbon
content makes the instrument more susceptible to rust and corrosion.
During manufacturing, the instruments are subjected to a passivation and polishing
process in order to make the stainless steel as corrosion-resistant as possible. Passivation
and polishing removes the carbon molecules from the instrument surface, forming a layer
which acts as an outer corrosion-resistant seal.
The passivation process leaves microscopic pits where the carbon molecules were
removed. Polishing is therefore important to create a smooth surface and a layer of
chromium oxide on the surface of the instrument.
Be careful with new instruments
A continuous passivation process occurs through repeated exposure to oxidizing agents in
chemicals, soaps, and the atmosphere. Regular handling and sterilization will further build
up and increase the layer of chromium oxide protecting the instrument from corrosion.
Older instruments thus seem to be less subject to corrosion than newer ones. Newer
instruments have not had the time to build up a thicker protective chromium oxide layer.
Since the passive layer increases over time, the risk for corrosion damage will also decrease,
but on every passive layer there are areas that are more susceptible to corrosion attacks
due to the local crystallographic structure. These areas are always more susceptible when
in damp or aqueous environments.
Five times longer lifespan with tungsten added
Tungsten (Wolfram, W), is an exceptionally strong refractory metal used in steels to
increase hardness and strength.
Tungsten carbide is a dense, metal-like substance, light gray with a bluish tinge. For
fabrication, powdered tungsten carbide is mixed with another powdered metal, usually
cobalt, and pressed into the desired shape, then heated to temperatures of 1,400°–
1,600° C; the other metal, which melts, wets and partially dissolves the grains of tungsten
carbide, thus acting as a binder or cement.
The cemented composites of tungsten carbide–cobalt when used, for example, in the
cutting edges of scissors, makes them last up to 5 times longer than ordinary stainless
steel blades.
Facts and features about quality processes (continued)
Quality assurance and quality control are commonly misunderstood and seen as purely
administrative tasks in many healthcare settings. It is important to emphasize that quality
processes are one of the most important tools for development in every organization.
Quality assurance activities are intended to prevent non-conforming procedures and/or
results and should include quality control activities.
Quality systems should apply to the organizational structure, responsibilities, procedures,
processes and resources for implementing quality management.
Quality systems should identify, recommend, or provide solutions for quality problems
and verify their implementation.
Quality indicators must be based on ordinary daily activities, they should be easily
recognizable and understandable by all personnel involved. Quality procedures and
development are always most effective when as many people as possible are involved
and should therefore be integrated as a natural part of all activities carried out at the
healthcare premises.
Optimal security for washer disinfectors
and sterilizers. If for any reason goods are
suspected of not being sterile, it should be
possible to trace them to local units, in order to
be withdrawn and returned to the sterilization
unit. Furthermore, to assure optimal security,
process data from washer-disinfectors and
sterilizers must be documented.
if
It
Call back items with risk of being nonsterile. A crucial part of traceability systems
is the possibility to call back sterilized articles
process control of sterilizers shows process
failure.
is also important that items are called back
with immediate alert – computer-based
traceability programs make this possible.
Sterility depends on handling and
storage. Instruments and materials should be
stored in a cool, dry and dark place. Articles
made of rubber or latex will age even if stored
unused. During transport it is also important
that instruments are stored in a manner
that prevents misplacement and transport
damages. Success in maintaining sterility
greatly depends on proper handling and
storage. Instrument corrosion might well be
the result of improper storage conditions such
as humidity and temperature fluctuations.
Quality systems to meet predetermined specifications
The term “quality system” encompasses all activities that are necessary to assure that a
device or procedure meets all predetermined specifications and the desired outcome.
This includes assuring that processes are controlled and adequate for their intended
use and/or purpose, that documentation is controlled and maintained, that equipment is
calibrated, validated, inspected, tested, etc.
Intended use – intended purpose ? What is the difference?
“Intended use” refers to the manufacturer’s statement regarding what the medical device
should be used for and under what circumstances. “Intended purpose” is what the user
wants the device to carry out.
For example, the intended use of a hospital steam sterilizer with a final post-vacuum
drying phase is to deliver sterile wrapped and dry goods.
One important task in every quality system is to define both the intended use and the
intended purpose so as always to be sure that the appropriate equipment is being used
for the right procedures and to follow given manuals and instructions.
Following given instructions not only concerns the handling of equipment but also
installation, service, maintenance, validation of equipment as well as transport and
storage of sterilized items etc. Continuous training of personnel is another important
quality issue.
Risk analysis - a major tool for improvement
Identifying faulty production or discrepancies from desired final results not only means
finding the major discrepancies – they will usually be found and identified even without
a quality assurance system. The important task is to find all minor and often unidentified
discrepancies or even better to identify potential risks. Finding potential risks through risk
analysis gives greater possibilities to work with the prevention of discrepancies from given
standards.
Emerging nosocomial infections heighten the demands for quality
In the current worldwide situation of emerging nosocomial infections and increasing
antimicrobial resistance, hygiene and infection control must be seen as one of the key
target areas for quality assurance and quality improvement.
This must include documented safe use of disinfectors and sterilizers as well as traceability
and the possibility of tracking instruments and articles down to patients and critical
procedures carried out.
Based on sound documentation, analysis of non-conforming results must be carried out
not only to increase efficiency but foremost to prevent nosocomial infections due to nonconforming handling of disinfected and sterilized articles.
Increased demands on sterile goods
In a traceability system, all sterilization processes should be registered and documented.
It should be possible to trace sterile goods from the disinfectors (washers), packing area,
sterilizers (autoclaves) and dispatch area and preferably to the unit receiving the goods.
Provided the goods have been used, it should also be possible to trace them to the
patients for whom they were used.
Facts and features about quality processes (continued)
Too many instruments – a common problem
The type of equipment and the type of procedures in use at the clinic to a very great
extent determine the safety margin of the decontamination. A very important issue, one
that is often overlooked, is the logistics of instruments.
A common problem in many healthcare
settings is an abundance of instruments,
which contributes to a more difficult and
time-consuming procedure to keep
track of all instruments and to make sure
that storage and sterile conditions as
well as packaging/wrapping conditions
are maintained.
It is always necessary to carry out an
inventory of instruments and items
in stock. Manual inventories are
highly manpower-consuming, while
computer-based traceability programs
help to facilitate the inventory process.
Logistics and storage
Materials and instruments are often placed in several of the clinic’s
storage facilities, from larger ones to the sterile supply area or
cupboards in the treatment rooms. Having many storage facilities
makes it difficult to survey how many articles and instruments there
are really in use. The number of instruments, items and articles
must never be too high, but there is always a minimal number of
everything that must be kept in stock in order to never end up in
a situation of not being able to carry out certain procedures due
to “lack of stock”.
Using bar-codes and computer-based traceability systems where the predefined lowest
critical number of all instruments, items and articles are always kept under control will
reduce the risk that the items are in the wrong place, or non-existent. To compensate
for the risk of not having the necessary equipment, most healthcare settings have an
over-supply of almost everything, just to have a safe margin. This surplus leads to
increased need of space for storing, increased cost for keeping storage facilities at the
right temperature and humidity levels, as well as increasing the time and number of staff
needed for inventories. All of this adds to the economical burden of healthcare costs.
Simplified identification of instruments for re-sterilization
Having fewer instruments in circulation makes it easier and safer to locate goods that
should be re-sterilized and re-disinfected and assures that there is always up-to-date
information on what instruments are needed in the surgery. Higher security is a result of
always having the right materials and instruments in the treatment area.
Traceability equally important on items from suppliers
Traceability systems should not only cover articles disinfected and sterilized in the healthcare
setting in question, but there should also be traceability on items from different suppliers.
Many items are delivered factory-sterilized but even factory sterilization processes can
eventually result in non-sterile products or other non-conforming results, and therefore
need to be called back to the supplier.
Delivered goods and articles will have different expiry dates, some articles need to be
stored under specific conditions etc, which calls for effective inventory systems to maintain
the highest possible quality.
Another important area for traceability and tracking is the use of pharmaceuticals and
chemical substances.
Traceability system to tailor-make instrument needs
Traceability systems facilitate the flow of instruments and goods the whole way between
treatments, via the sterile area, to storage. Traceability systems, documentation and analysis
of the handling of instruments as well as keeping track of the total load of instruments and
articles in circulation is thus a good way to improve the overall economy.
Computer based systems and bar-codes
To be effective, traceability systems are best maintained with the help of computer-based
software. It is of course possible to maintain a good and efficient quality program including
traceability with manual systems. However, computer technology facilitates possibilities
to make overviews and analyses that were almost impossible not so many years ago.
Bar-code for fast and efficient identification
Barcodes offer the best and fastest system for instrument identification when integrated
into computer-based software.
Computer-based traceability systems help maintain effective control of sterile supply
purchases, stock and production, as well as allowing financial analyses, price calculations
and the invoicing of dispatched units. It also makes it possible to track instruments to
specific departments and even down to individual patients and surgical procedures.
Economical benefits through knowledge of turnover rate
When the location and turnover rate of the instruments are known, the total number of
required instruments can be reduced. With increased possibilities for on-line purchasing
over the internet, computer-based logistic systems can be used for automatic ordering
when the stock of items reaches the critical minimum level. This reduces the staff time
needed to order new goods.
Facts and features about quality processes (continued)
Loss of valuable time
Unstructured handling of instruments results in losing valuable
time and raises the risk of reducing security and disregarding
aseptic materials. To ensure proper quality assurance on all
processed instruments, adequate documentation in the form of
written work instructions clearly defining and describing every
step in the decontamination – disinfection – sterilization process
must be on hand.
This should also include risk analysis, methods for validation and process control as well
as defined configurations for loading washer-disinfectors and sterilizers. Secure handling
of instruments also leads to minimizing the risk of prick and puncture wounds, through
less stress.
Traceability and quality procedures improve overall competence
Quality assurance activities, including systems for traceability, are not only essential purely
from safety, logistic and economical standpoints. They are also and probably foremost an
important way to guide an organization in choosing the proper competence development,
not only in the form of recruitments of personnel and other resources but, more importantly,
in the continuous education of staff at the site.
Computer-based systems for traceability and logistics
also have a great benefit in crossing language barriers.
With current technology it is possible to work out of
the very same database and have screen interfaces
in different languages depending on who is working
behind the screen.
It will also be possible, instead of text, to show different
procedures and, when working in the sterilizing unit,
pictures of different instrument set-ups to make sure
that everything is in accordance with predefined
requirements.
Economy – the last (and a less effective) factor to identify reduced success
The success or failure of an organization is often measured mainly in terms of financial
results and on a short-term basis. But in organizations that work with quality assurance
and where the personnel is involved in a continuous quality development program and
can also influence their work by suggesting quality improvements, one of the very early
warning signs is usually seen in the personnel’s involvement in quality procedures. The
phenomenon can be detected and analyzed long before the economy is affected. Usually,
overall economy is the last factor in a long chain of events.
This is the major, and unfortunately most often overlooked, benefit of working with quality
processes. The more transparency and the more different procedures and their effects
further on in the production line can be visualized and understood among the personnel
involved, the more the personnel will be apt to participate in daily quality improvements
– which is one of the most important factors both for maintaining high quality and for
achieving the best possible financial results of a given organization.
Discontinue all procedures that don’t improve the final result
The terms effectivity and efficiency are often misinterpreted as the need of producing
more in the same given time. The most important consideration should actually be to
identify as many procedures as possible that add no value to the final result, since they
are merely a waste of time and resources. When unnecessary procedures are identified,
all these resources can instead be focused on adding value and improving quality.
The possibilities generated by modern computer technology must be integrated at all levels in healthcare. It is also important that computer technology is incorporated by simple
and easily understandable means and equipment so as not to be an additional burden
to the personnel involved, but rather a tool to improve quality and efficiency. Software
must therefore be tailored in such a way that necessary information can be retrieved at all
levels and give feedback directly on local procedures. In the field of hygiene and infection
control, this comes down to documentation of manual and machinery performance to
ensure the highest possible security as well as traceability and tracking of procedures,
instruments and articles.
Incorporation of these practices into the daily procedures, and continuing to work with
their further development, results in more rapid dissemination and integration of the final
results, evidence-based processes, efficiency, safety and overall healthcare economy.
Traceability demands placed on sterile
goods and their processing should include
to possibilities to:
• trace sterile goods from reception in
the sterile services department, through
the washer-disinfectors, packing area,
sterilizers, further to the storage area
and delivery to the costumers (hospital
departments), the use on patients and then
back again;
• identify unique instruments or unique
sets of instruments used on a particular
patient;
• identify the set with the patient and
all previous and subsequent patients on
whom that item has been or will be used;
• monitor all sterilizer processes;
• monitor
all
washer-disinfector
processes;
• monitor staff operations on specific
instruments and trays;
• generate tray lists and labels;
• keep control of maintenance of
equipment as well as instruments and
trays.
Facts and features about quality processes (continued)
Performance qualification , measuring steam temperature and pressure
For performance qualification, a number of thermal sensors (thin wires) are placed in the
sterilizer chamber and inserted into the packages, against the items to be sterilized. Each
wire has a so-called thermal sensor at the tip, which measures the temperature inside the
chamber and on the surface of the items selected as reference loads for the actual cycles,
in order to determine that acceptable surface sterilization has been achieved. The thermal
sensors, together with an extra pressure sensor, are connected to measuring equipment
that registers temperature and pressure for each phase of the process. The registered
measurements are then compared with the specifications in the relevant standard. The
actual temperature measured on the goods and items in the load is compared with
the theoretically calculated temperature which should apply at the measured chamber
pressure.
It is important that the entire chamber and the packaged goods reach the vaporization
temperature (boiling point) at a certain given pressure for a certain time for the processes
to be tested. +134ºC and 3.0 atm or +121ºC and 2.0 atm.
In order to have as rapid a turnover of instruments as possible, the sterilizing time in the
steam sterilizer should be minimal, at a minimal temperature at the relevant pressure. It
is therefore important that the relationship between temperature, time and pressure is
maintained, not only in the chamber but also in the packaged goods.
When the sterilizer enters the sterilizing phase, the entire chamber including the packaged
goods must maintain an exact temperature and this may not vary by more than 2.0ºC
among the measuring points in the load. The reading from each separate thermal sensor
may not vary by more than 1.0ºC during the sterilizing phase.
Validation, Process Challenge Devices and Quality Indicators
Health care providers must be able to rely on sterility
It is vital that sterilization procedures always promote the same level of safety and efficiency.
Requirements include routine biological, mechanical and chemical monitoring to ensure
that all parameters of sterilization are met before using the instruments on patients.
The quality processes at the sterilizing unit must be such that the healthcare provider
always can rely on the goods meeting the sterility demands when being used. In this
sense, the sterilizing unit, regardless of its size, will be an important ”manufacturer” of
sterile items.
It is not feasible to check whether individual instruments or sets of instruments are sterile
or not after sterilization. To do this, the wrapping would have to be opened and test
samples taken from the sterilized goods – which would of course mean that any package
checked would become unsterile and could not be used. For this reason, every single
procedure in the reprocessing of sterile instruments has to be carefully monitored to make
sure that the ”production line” will render a sterile result.
There are a number of studies showing uncertainty about sterilizing equipment. To reliably
provide sterile goods, it is necessary that the sterilizing equipment (the autoclave) is
regularly checked and otherwise correctly operated.
The performance of a steam sterilizer shall be checked regularly with exact physical
methods of measurement. The full procedure includes validation, commissioning and
qualification of performance.
Validation of steam sterilizers to conform with standards
Qualification of performance requires determining on location that the steam sterilizer
fulfils these basic criteria and that it functions with a load typical for the healthcare setting
in question. As the qualification of performance applies to all steam sterilizers that produce
sterile goods, the load used for qualification of performance must therefore be a typical
sterilizing load. The reference load / loads should subsequently be used for repeated
testing – details of the load and the location of each separate thermal sensor should
therefore be documented and filed for future reference.
Process Challenge Devices for safer sterilization
Process monitoring should be carried out on every sterilizing process intended to
produce sterile goods. This can be done using physical, chemical or biological indicators.
Proper and complete monitoring of sterilization procedures should routinely include a
combination of different process parameters. It is important to bear in mind that indicators
do not actually prove that sterilization has been achieved, only that parameters have been
attained.
Don’t forget visual inspection
Process challenge devices add quality control, but to
inspect visually that everything is really clean is still one of
the most important controls after the completed cycle in the
washer-disinfector and before sterilization
Facts and features about quality processes (continued)
Process Challenge Devices
• Physical in the form of a printer or so-called pressure and temperature loggers.
• Chemical, in the form of integrated indicators, which give a color indication depending on pressure,
saturation of steam and temperature.
• Biological, in the form of spore tests (B. Stearothermophilus). Although spore tests reveal whether the
sterilization process in question can inactivate certain bacterial spores that are particularly resistant to heat,
such tests provide no detailed information about the actual process. Furthermore, biological indicators are
difficult to standardize and there may be variations in heat resistance between different batches. Biological
indicators assess the sterilization process directly by using the most resistant microorganisms. Bacillus sp.
spores used in biological indicators are more resistant and present in greater numbers than the common
microbial contaminants found on patient care equipment. Inactivation of the biological indicator strongly
implies that other potential pathogens in the load have also been killed. However, spore tests can, with the
reservations described above, be a means of monitoring the function of steam sterilizers, but are not really
adequate for full monitoring of the function of an sterilizer intended to produce sterile goods.
There are also specific test methods to monitor the functioning of sterilization cycles:
• The Bowie & Dick Type Test, which is used to verify conditions in the sterilizer chamber for sterilizing
porous loads such as textiles.
• The Helix Test, which is used to verify conditions in steam sterilizers for sterilizing hollow instruments
(”hollow loads”).
When using biological indicators, they should be placed where sterilization is important to test, e.g. as in
the left picture, inside the syringe. Biological indicators can either be sent to a microbiology laboratory or,
even better, cultured directly on site.
Chemically integrated indicators can be tailored for specific sterilizing cycles. As process challenge devices
they react to time, temperature and the quality of saturated steam. The test device can be placed in the
type of load where sterility is essential. Readings can be made directly after the sterilization process. Left
within the wrapping, the process challenge device can also be monitored when the instrument set in
question is about to be used. This gives possibilities for a double check.
Goods must be sterile at point of use - requires wrapping
Steam sterilizers add the possibility of packaging the goods. Today’s demands on sterile
goods are that the goods are to be sterile the very moment they are to be used, and they
must therefore be packaged in special, tight packages that allow nothing to penetrate
them.
It is important to note that packaging material itself is a porous load (paper, textiles) and
should be handled as such. All packaged/wrapped goods require sterilizing in steamsterilizer processes with pre- and post-vacuum cycles.
Before the holding time (the actual sterilization phase in the whole sterilizer cycle) starts,
the air inside the package must be evacuated at the same time as the steam penetrates
and heats up the goods. Virtually all air must be evacuated during pretreatment so that
the saturated steam can affect the goods during the sterilizing phase.
Residual moisture in the packaging material after sterilization will act as a potential pathway
for microorganisms to penetrate the package. Post-vacuum is an effective method for
drying the load and removing any remaining moisture.
After sterilization, the goods must be maintained in a sterile state during
transport and storage, until used. The packaging material must therefore meet
stringent criteria. In order to assure this, all quality assurance procedures are
of extreme importance, including validation, performance qualification and
process challenge devices.
Facts and features about quality processes (continued)
The Bowie&Dick type test is a special application of a chemically integrated indicator that
can be used as a process challenge device simulating a large porous load. Textiles, for
example surgical draping, are important large porous loads.
The Helix test is a special application of a chemically integrated indicator that can be used
as a process challenge device simulating a hollow load and hollow instruments.
It is not only instruments with long hollow lumens, such as endoscopes, that are hollow.
All instruments with hinges or parts held together by screws are considered hollow.
In all testing of sterilizers it is important to bear in mind that it is not the testing
itself that is of importance but rather what answers are crucial to get from the
different process challenge devices.
When the goods are released, the sterilizing personnel shall be able to assure,
as far as possible, that goods are sterile. This is not possible after a single type
of test, but only after numerous tests of several kinds, since they challenge the
process for different types of loads.
Different kinds of loads
The result of steam sterilization is influenced partly by the kind of material the items are
made of, and partly by the shape of the items. These are classed as follows:
• Homogeneous / solid instruments
• Tube-shaped, hollow instruments
• Porous material, textiles
It is important to evacuate air during pretreatment so that saturated steam can be in
contact with the goods during the entire holding time. Two other very important factors
that influence the result of a sterilizing process are whether the items are packaged and
the shape of the package.
In principle, sterilizing can be carried out with:
• unpackaged goods;
• single wrapping, e.g. instruments on covered trays or on instrument racks;
• double wrapping, e.g. a covered tray inside a foil packet.
If the instruments are open in the sterilizer, it is easy for the steam to contact the surface
of the goods, which are easily heated up on contact with the condensing water vapor.
Conditions are different for packaged goods. The properties of the packaging material are
important for achieving sterility and maintaining sterility during storage.
What is the importance of process challenge devices?
There should also be a system for tracking sterilized goods. Goods used for sterile
intervention (surgery) should be traceable to the specific sterilization procedure. This is of
particular importance in larger clinics with a number of operators and even more important
when CSSUs (central sterile supply units) handle goods for a large number of users, as
well as when sterile supplies are sourced externally.
Process monitoring should be carried out on every sterilizing process intended to produce
sterile goods. This can be done using physical, chemical or biological indicators. It is,
however important to bear in mind that indicators do not actually prove that sterilization
has been achieved, only that parameters have been attained.
Not only the sterilizer process should be scrutinized
To ensure proper and complete elimination of all biological material prior to sterilization, it
is crucial to check and handle a washer-disinfector correctly and, above all, to know how
to load it to clean and disinfect the instruments efficiently.
There are several interesting test kits on the market. One of the greatest advantages of
using a test kit is the opportunity to test and understand the best way to load and handle
the washer-disinfector.
The test kits can also show the flaws in the handling of the washer-disinfector. These
might be simple flaws like installation failure, the disinfector being too old, the pump being
worn out, the wrong kind of cleaning or rinsing agent, soft or hard water, badly perforated
trays or simply that the washer-disinfector is overloaded. The latter is by far the most
common problem!
Ultrasonic cleaners usually have a lifecycle of 3-5 years depending on the frequency of
use (number of running cycles). They must be checked on a regular basis to verify that
the cleaning capabilities are properly maintained.
This can be done either by using commercially available challenge devices or by using
ordinary aluminum foil. If aluminum foil is allowed to hang freely down into the water bath
of the ultrasonic cleaner, the pulsating waves should be strong enough to tear holes all
over the surface of the foil.
Facts and features about quality processes (continued)
Process challenge devices for washer-disinfectors and ultrasonic cleaners
The cleaning of instruments and articles is the all-important issue in decontamination,
disinfection and sterilizing. Not only the microorganisms (i.e. bacteria, virus, fungi etc.)
have to be removed during the cleaning process, but also organic substances (e.g. saliva,
blood, tissue remnants). These substances consist of carbohydrates, fat and protein and
if they are not removed from the instruments before sterilization, the sterilization itself will
prove inefficient.
For this reason, process challenge devices for washer-disinfectors and ultrasonic cleaners
are even more important than similar devices for sterilizers.
Like sterilizers, there are several different ways to evaluate the
capacity of washer-disinfectors, all aiming to give indications of the
efficacy to remove residual bioburden on the load.
Still, manual inspection of all instruments before wrapping and
sterilization must be regarded as the most important method of
cleanliness control!
“Sterile” does not mean clean and safe - conclusions
Most equipment-associated infection is due to inadequate cleaning and
disinfection.
Medical devices heavily loaded with microbiological material will be more
difficult to sterilize than those that are only lightly contaminated and must
therefore be thoroughly cleaned to reduce organic material or bioburden
before disinfection and sterilization.
Automated processors, e.g. washer-disinfectors and ultrasonic cleaners,
improve the quality of the decontamination process and offer the safest, most
reliable option, provided they are suitably monitored and maintained.
A general principle is that all items used to penetrate soft tissue or bone,
enter or contact the bloodstream or other normally sterile tissues, should
be sterilized and be sterile at the point of use.
If washer-disinfectors are technically defective or are incorrectly operated,
microorganisms can be detected on medical devices, and may subsequently
be transmitted to patients.
The result of sterilizing procedures depends on the number of microorganisms
and other biological material present on the article before inactivation and
the resistance of microorganisms to the sterilization process.
Packaging material itself (paper, textiles) is a porous load and should be
handled as such. All packaged/wrapped goods require sterilizing in steamsterilizer processes with pre- and post-vacuum cycles.
Saturated steam under pressure is by far the quickest, safest, most
efficient and most reliable medium, known for the destruction of all forms
of microbial life.
Process monitoring should be carried out on every sterilizing process
intended to produce sterile goods. This can be done using physical,
chemical or biological indicators.
It is important to bear in mind that indicators do not actually prove that
sterilization has been achieved, only that parameters have been attained.
To comply with GMP (Good Manufacturing Practice), manufacturers are
obliged to provide full details on how to decontaminate the reusable
devices they supply. This should include details of compatibility with heat,
pressure, moisture, processing chemicals and ultrasonics.
Facts and factors about hand hygiene
The most important single procedure of all!
Hand disinfection with alcohol-based hand disinfectant: always before
handling clean goods and after handling contaminated/used goods – one
of the most important single procedures to prevent the spread of infectious
diseases!
Technique for handdisinfection.
Figure from: Infection Control: Basic Concepts And Training. Second Edition
International Federation of Infection Control 2003
Hand hygiene and personal protection
Hand hygiene – hand disinfection
There is conclusive evidence that contaminated hands are responsible for transmitting
infections and are a major contributing factor in the current infection threats to hospital
in-patients. Hand hygiene prevents cross-infection in hospitals, but among healthcare
workers, compliance with guidelines is poor. For most hand disinfection purposes,
alcohol-based hand rubs are preferable to hand washing with soap and water. Alcoholbased hand rubs should be available not only at each bedside but also in all places
where disinfected hands are important, e.g. in the sterilizing unit, storage facilities etc.
An alcohol-based hand-rub requires less time, acts faster, is less irritant to the skin of the
hands, and contributes significantly to sustained improvement in compliance associated
with decreased infection rates.
The microorganisms that occur on the skin of the hands and under the fingernails consist
partly of so-called normal or permanent skin flora, and partly of so-called transient skin
flora. The permanent skin flora comprise microorganisms that normally colonize the
skin and under the fingernails. These bacteria are usually nonpathogenic and provide a
certain protection against pathogenic bacteria. The transient microflora of the skin can
comprise many different types of microorganisms, depending on what the hands may
have touched, e.g. saliva or blood. Hand-washing, cleaning fingernails and disinfection
are primarily intended to target the transient microflora.
Part of the normal function of the skin is to provide a barrier protection against
microorganisms, wear and chemical agents and to regulate body temperature and
protect the body from dehydration. The skin is a kind of permeable membrane between
the body and the outside world. Under normal conditions, the thickness of the skin
remains constant, and the rate of regeneration of skin cells, determined mainly by external
influences (wear, chemical effect etc) is directed by different cellular functions.
The fat (glycerol lipids) normally found in the skin is an essential part of its barrier
protection. The cleaning agent in soap dissolves fat and splits protein and partly removes
the protective layer of fat from the skin, split parts of the outer epithelium and thereby
reduces the ability of the skin to maintain a fully effective barrier protection.
Hand-washing with soap and water for 15 seconds reduces the transient bacterial flora
around 10-fold; for 30 seconds, around 1000-fold. Washing with soap can, however, have
the opposite effect – increasing the bacterial flora on the hands, partly as described above,
by disrupting the protective barrier of the skin of the hands and partly because certain
strains of bacteria can colonize and multiply in soap solutions. This applies particularly to
pseudomonas and liquid soap in dispensers.
Hand disinfection with alcohol-based disinfectant for 30 seconds
reduces the bacterial flora on the skin of the hand 10,000-fold; and
for 60 seconds up to 100,000-fold and is thus markedly more effective
than washing with soap and water.
Facts and factors about hand hygiene (continued)
Apart from the concentration, other determinants of the effectiveness of hand disinfection
are the duration of contact and the volume (amount) of disinfectant. Using small amounts,
less than 1ml, offers no advantage over washing with soap and water. A good guide is
that if the hands feel dry 10-15 seconds after rubbing in alcohol-based disinfectant then
the volume used was inadequate. The time for this sensation to be noticed (until the
hands feel dry) should be at least 30 seconds, preferably 60 seconds.
Protective gloves
Gloves can prevent transmission of infection by reducing the degree of soiling of the
hands. Change to a fresh pair of unused gloves on a regular basis. Disinfectant on gloves
can damage or disintegrate the gloves, thereby reducing the protection they are intended
to provide. Gloves should not be used as a substitute for proper antiseptic work routines.
Gloves are, however, an excellent complement.
Hand hygiene more important with the use of gloves
The use of gloves actually increases the need for hand disinfection. There is very little
air inside a well-fitting glove, and this can stimulate the growth of anaerobic bacterial
flora. Anaerobic bacteria are often the most aggressive pathogenic bacteria. The moisture
(perspiration from the hands inside the glove) provides an excellent substrate for the
bacteria. This so-called “glove juice” is a potential risk to the patient, but mainly a risk
of deterioration of the skin of the hands of the wearer. Incorrect handling of gloves is
a frequent underlying cause of sensitivity reactions and development of allergies. In
particular this applies to washing hands with soap and water and then inserting into a
glove a hand that is still moist and bears residual traces of soap! Once again, the use of
a good alcohol-based disinfectant is preferable.
Protection against prick- and puncture wounds
Gloves should be made of a smooth, elastic material with good compressive and tensile
strength. Gloves should have very high puncture resistance, as the major reason for
wearing gloves is to protect from prick and puncture wounds. One of the main reasons
for healthcare personnel to become cross-infected is prick and puncture wounds when
handling soiled sharp instruments!
Medical gloves (examination gloves) must
never be used when handling instruments in
the decontamination and sterilizing area.
Use only proper gloves intended for cleaning
and handling contaminated goods !
Alcohol-based hand disinfectants
The most common hand disinfectant is 70 volume-% ethyl alcohol, giving a disinfectant
effect corresponding to about 77 vol-% ethanol or 60 vol-%. isopropyl alcohol (isopropanol).
Propyl alcohols (e.g. isopropanol) are volatile at high concentrations.
Hand disinfectants based on isopropanol therefore usually contain 45 vol-% isopropanol
together with some other alcohol or chemical disinfectant in order to attain a concentration
of about 60 vol-% isopropanol. The occupational hazards of alcohols are negligible.
Alcohols have a dehydrating effect on the skin of the hands, and this can also cause
a similar effect to the one described above with respect to hand cleaning with soap
and water. In order to avoid dehydration of the skin surface, alcohol-based disinfectants
contain some kind of rehydrating agent, usually 1-3% glycerol.
In general, alcohol is an effective disinfectant for vegetative bacteria, including MRSA
(methicillin resistant staphylococcus aureus), mycobacteria, fungi and most viruses e.g.
encapsulated viruses such as herpes simplex virus, HIV, influenza virus, hepatitis B-virus
and hepatitis C-virus.
Alcohols are not as effective against naked viruses such as Hepatitis A-virus and polio
virus. To compensate for this, a somewhat higher concentration of alcohol is required, or
the addition of other disinfectant agents. Alcohol has no effect against bacterial spores
and protozoa (unicellular animals, e.g. amoeba).
Wash hands with soap at the beginning of the working day and thereafter
only when the hands are visibly soiled.
Hand disinfection with alcohol-based hand disinfectant: always before
handling clean goods and after handling contaminated/used goods.
d disinfectant based on ethanol or isopropanol, with a disinfectant effect
corresponding to about 77 vol-% ethanol, or alternatively isopropyl alcohol
> 60 vol-% (or equivalent).
Hand disinfectant containing 1 - 3% glycerol as a rehydrating agent.
Use liberally: 3 – 5 ml.
Apply thoroughly to all the skin of the hand – don’t forget the fingertips
The time to take effect is at least 30 seconds (before the hands begin to
feel dry
If necessary the hands should be rinsed in cold running water before hand
disinfection.
Facts and factors about hand-hygiene (continued)
Protective clothing shall always be worn in all areas of the sterilizing unit,
regardless of the size of the unit.
The clothing as well as the personal hygiene are both essential parts of the
barrier protection within the sterilizing unit.
Different types of protective clothing are needed in different parts of the
decontamination and sterilizing process.
In order to separate as much as possible and to maintain crucial barriers, the
geographical boundaries of the sterilizing unit are also of importance.
There must be “one-way traffic” only through the sterilizing unit as well as
blocked ways for both personnel and goods.
In all healthcare settings, irrespective of size and the type of care provided,
the quality of all services provided is highly dependant on the quality provided
within the sterilizing unit.
Cross-infection control, hygiene and sterilization must be seen as
today’s most important tasks in all healthcare systems.
The continued use of inferior equipment as well as non-updated
clinical procedures, is difficult to justify on professional, moral,
ethical or economical grounds.
Personal hygiene important in health and medical care
Every human being sheds around 104 skin particles/minute while walking around. Of
these skin particles, around 10% are carriers of bacteria. Each individual sheds 10008000 bacteria-carrying particles/minute. Both aerobic and anaerobic skin bacteria are
released into the atmosphere. Studies of operating rooms show that anaerobic bacteria
comprise around 30% of all bacteria in the air in the operating room.
The number of bacteria-carrying particles in the air depends on how many people are
present, the level of physical activity, how they are dressed and the type of ventilation.
The normal bacterial flora of the surface of the skin varies between different parts of the
body:
Skin region
Scalp
Axilla
Abdomen
Forearms
Hands
CFU/cm2 (colony forming units)
1 x 106
5 x 105
4 x 104
1 x 104
4 x 104 -- 5 x 106
(104 = ten thousand; 105 = one hundred thousand; 106 = 1 million)
Bacteria on the skin are classified as either transient or permanent flora. The transient
bacteria are those that may be temporarily present on the skin in the surface layers and
are relatively easy to remove with ordinary hand hygiene. The permanent bacteria colonize
the deeper layers of skin and are more difficult to remove. It has been shown that the
skin of the hands of health personnel can become permanently colonized with diseasecausing bacteria.
Due to the shedding of bacteria from the human body, the use of protective clothing as
well as personal hygiene are of great importance when it comes to the control of crossinfection risks.
The passage of skin bacteria through protective clothing has been demonstrated, but
unless the clothing is wet through, only very few bacteria are involved. There is every
justification for changing surgical coats at least once daily. Clinical clothing (scrubs) should
be laundered frequently and at temperatures high enough to kill the infectious agent (at
least +70ºC).
Hair protection to protect from inferior wound healing
Transmission of infection from hair is not regarded as an issue in healthcare settings. Hair
strands can, however, carry bacteria, not only the person’s own but also those from the
environment. Strands of hair can therefore contaminate surgical wounds and instruments
if they alight on them.
A major problem with strands of hair is that they can cause wound granulomas if they for
some reason end up in the surgical site on patients. Strands of hair cannot be broken
down by the human body’s immune system. Strands of hair are very difficult to detect,
which is why hair protection is of importance when working in the sterilizing unit.