Download Principles of Infection Control

Principles
of Infection Control
Dr J Mooney, PhD
Categories of Disease

Contagious disease /infection


transmissible diseases (i.e.: transmit from person to person)
by


physical contact with the person suffering the disease
casual contact with their



Non-contagious disease / infection

requires a special mode of transmission between persons or host







bodily secretions including exhaled particles
objects they have touched
vector species (e.g.: anopheles [malarial] mosquito)
non-casual transfer of bodily fluid (e.g.;\ transfusions; needle sharing;
sexual contact)
genetic inheritance (autosomal dominant; autosomnal recessive)
environmental factors (e.g.: goitre formation and low iodine intake)
behavioural (e.g.: cigarette smoking)
usually more harmful and painful than contagious diseases.
The boundary between categories is not perfectly drawn

E.g.: TB is contagious and also subject to environmental factors
Infection



Invasion of body tissues by disease-inducing
microorganisms and
The reaction of those tissues to the
microorganisms and/or their toxins
NB: The mere presence of microorganisms
without tissue reaction is not evidence of infection



Concept of MO load
>106 MOs / mm3 affected tissue
NNB: >103 MOs / mm3 affected tissue in DM
Eukaryocytes
*
**
50% Biomass
Eukaryocyte organisms





nucleated cells **
Single celled animals and plants
All multi-celled animals
All multi-celled plants
NB: Biomass = Total mass of living matter within a
given unit of environmental area
Prokaryocytes



**
Prokaryocytes = non-nucleated MOs *


*
e.g.: bacteria
Found everywhere - sea water, soil, air,
gastrointestinal tracts, hot springs, and in rocks
Cover all non-sterilized surfaces
Prokaryocyte organsism are estimated to make up
remaining 50% of earth’s biomass
Microorganisms (MOs)

MOs are a very diverse group of unicellular eukaryotic and
prokaryotic organisms essential to all ecosystems



MOs live in all parts of the biosphere where there is
liquid water


Include bacteria, fungi, archaea, and protists;
microscopic plants (green algae); and animals such
as plankton and the planarian.
Some microbiologists also include viruses, (others do not, classing
viruses to be non-living organic material)
Soil, hot springs, on the ocean floor, high in the atmosphere and
deep inside rocks
MOs are critical to ecosystems



Nutrient recycling where they act as decomposers
Nitrogen fixation: vital part of the nitrogen cycle
Airborne MOs may play a role in precipitation and weather
Bacteria

Prokaryocytic MOs, ~1-5 X10-6mm long

surrounded by a cell wall,






Also harbor small pieces of DNA called plasmids
Plasmids can transfer via bacterial conjugation.
Reproduce by binary fission
Do not undergo sexual reproduction.
Some species form extraordinarily resilient spores


Often aggregate into multicellular colonies
Non-nucleated - Have a single loop of DNA


lack membrane-bound intra-cellular organelles
Can function and reproduce as individual cells


provides strength and rigidity
Mechanism for survival, not reproduction.
Under optimal conditions bacterial colony can double every 10 minutes
Bacteria (contd)


Vast majority of bacteria are harmless or beneficial
Some are pathogenic and cause infectious diseases, e.g.:




Pathogenic bacteria also cause infections such as


TB caused by Mycobacterium tuberculosis
Pneumonia, caused by bacteria such
as Streptococcus and Pseudomonas
Foodborne illnesses, caused by Shigella,
Campylobacter and Salmonella *.
tetanus, typhoid fever, diphtheria, syphilis and Hansen's disease.
Bacteria can often be killed by antibiotics

ABs destroy their cell wall and then their D.N.A.
Typical bacterial skin, bone and soft
tissue infecting agents

Staphylococcus aureus


Streptococcus pyogenes


Cause localised infections, and
abscess formation
Causes rapidly spreading
infections, such as erysipelas
Eschericha (E) coli

Can cause deep infections, e.g.:
osteomyelitis
Gram Classification of Bacteria

Gram positive (G+ve) Bacteria





Thin cell wall
Take up gram stain (crystal violet granules)
More easily overcome by antibiotics (unless
bacteria develop ABx resistance)
E.g.: Staph aureus
Gram negative (G-ve) Bacteria




More complex cell wall
Tend not to take up gram stain
Less easily overcome by antibiotics
Eg.: Pseudomonas
Fungi


Fungi are eukaryotic (have nuclei)
Several unicellular species


Some fungi, e.g.: pathogenic yeast Candida albicans *,
can undergo phenotypic switching



E.g.: baker's yeast (Saccharomyces cerevisiae)
grow as single cells in some environments
or form filamentous hyphae (mats) in others
Reproduce


both asexually, by budding or binary fission,
and by producing spores (1-40 10-6mm long)


conidia when produced asexually
basidiospores when produced sexually.
Fungi (contd)

Fungi are usually saprophytes


Some can cause diseases in humans, animals and plants


Fungal infections are more common in the immuno-incompetent
population (e.g.: DM, stressed), affecting skin and nails *
Fungi are non-susceptible to antibiotics


most common cause of diseases in crops and other plants
Life threatening fungal infections in humans most often
occur in immunocompromised patients or vulnerable
people with a weakened immune system


MO that feeds on dead or decaying matter
both fungi and their hosts both have eukaryotic cells.
Most clinical fungicides are azole drugs
Common dermatophytes of skin
and nail

Trichophyton rubrum


Epidermophyton


‘Pencils’
‘Clubs’
Microsprorum

‘Spindles’
Viruses

Sub-microscopic MOs

20-300 nanometers in length (1nm = 1 x 10-9mm)

DNA enclosed within a capsule

Not susceptible to antibiotics

Pathogenic viruses include


Adenoviridae, Picornaviridae, Herpesviridae, Hepadnaviridae,
Flaviviridae, Retroviridae, Orthomyxoviridae, Paramyxovirida,
Papovaviridae, Polyomavirus, Rhabdoviridae, Togaviridae.
Cause diseases including

Smallpox, influenza, mumps, measles, chicken pox, ebola, rubella,
warts (VPs), shingles, polio, hepatitis B, HIV, etc etc.
Prions


Infectious pathogens that do not contain nucleic
acids.
Abnormal proteins whose presence causes e.g.:


scrapie, bovine spongiform encephalopathy (BSE; ‘mad
cow’ disease) and Creutzfeldt–Jakob disease (CJD)
Prions are very difficult to destroy by normal
sterilization processes

It requires up to 18 autoclave cycles to denature prion
protein
Control of Infection

Control of Infection


Infection Control


Policies and procedures used in hospitals and health
care facilities to minimize the risk of spreading
infections
Procedures and protocols designed to prevent or limit
cross-contamination in the health care delivery
environment
Purpose of infection control


To reduce the occurrence of infectious diseases
To prevent iatrogenic infection
Causes of Infectious Disease

Spread of Microorganisms



bacteria, viruses, fungi
or Infected material
via a Vector, i.e.:



Human to human contact
Animal to human contact (Zoonoses)
Human contact with



An infected surface
Airborne transmission of microscopic airborne droplets of
infectious agents / desiccated MOs / spore forms
Contaminated food or water
Infection control in hospitals
and other health care settings

Infection control is a formal hospital discipline



Hospital Acquired Infections = nosocomial infections, e.g.:






MRSA
CDiff
Affect ~ 5% of all hospital patients


Copied into all health care settings
Forms part of formal clinical governance procedures
Especially elderly, frail and immunocompromised patients
Medical procedures may introduce infection to patient
Infections also introduced by carriers (visitors / workers) are transmitted to
vulnerable cases
Increase morbidity duration of hospital stay
Increase mortality

Increased focus on hospital hygiene is not reducing incidence of CDiff (up
28% in 2011)
Examples of Infectious Diseases

Hepatitis B




Legionnaire’s Disease




Legionella (bacteria) contamination of air conditioning systems
Inhalation of infected water droplets
Treated with antibiosis
Ringworm (Tinea)




Viral infection causing liver dysfunction
Spread by sexual contact with infected person, or by contact with infected blood
No treatment
Fungal infection of skin
Contact with infected shed squames from human or animal
Treated with antifungals
Tetanus



Soil-borne bacterium causing severe muscle tetany and respiratory failure
Via break in skin
Antibiosis; muscle relaxants (Poor prognosis)
New threats and infections


Any control of infection protocol must prevent transmission
of all known, and also all as yet unknown, infectious agents
New diseases emerge constantly:



Many common infectious diseases have become resistant
to known treatments




HIV / AIDs
SARS (severe acute respiratory syndrome)
Most staphylococci now show a degree of antibiotic resistance
TB
Increased international and air travel exposes a naïve
population to unfamiliar MOs
Bioterrorism

Anthrax
Goals of infection control programs



Definition of formal precautions and
protocols that prevent / reduce exposure to
infectious agents
Introduction of immunization programmes
against preventable diseases
Restriction of exposure of health care
workers to infectious agents
Precautions that avoid and
control the spread of infections










Vaccinate against diseases for which a vaccine is available.
Wash hands often.
Cook food thoroughly.
Use antibiotics only as directed.
See a doctor for infections that do not heal.
Avoid areas with a lot of insects.
Do not purchase exotic animals as pets.
Do not engage in unprotected sex or intravenous drug use.
Find out about infectious diseases prior to travelling: take
appropriate vaccinations / preventative drugs.
Do not drink water that might be contaminated
Ebola
Some hope
Infection Control?
No hope
And….









Wear disposable gloves with all patients, since it is difficult to know whether a
transmittable disease is present or not.
Isolate patients who have a known infectious disease to decrease the risk of
transmitting the infectious agent to another person.
Hospital workers who come in contact with infected patients must wear gloves
and gowns to decrease the risk of carrying the infectious agent to other
patients.
Use air filtration mechanisms to remove MOs and spore forms
Dispose of all items of equipment used in an isolation rooms, or decontaminate
before re-use
House vulnerable patients (immunocompromised) in protective isolation to
decrease the risk of infection
Restrict all hospital workers with infections, including colds, from entry to
isolation rooms.
Handle infected materials so that numbers of infectious agents that may
become airborne are minimized
Hospital ventilation systems must be maintained to prevent recirculation of
contaminated air.
Historical Perspectives
Surgery was very chancy before there was an
understanding of infection control

A surgeon operated in a blood- and often pus-stained coat




Infection was expected within 3-4 days (laudable pus)




Instruments were only rinsed to remove obvious contamination
Wounds were packed with moist lint or raw cotton, or plugged with
cotton wool soaked in collodion
Bandages were kept damp
Thought to be the essential sloughing off of the lining of the wound
It allowed ‘clean tissue’ to form prior to healing
Healing without pus formation was an unexplained mystery
In contrast, damnable pus was feared (death sentence)

= infected gangrene
From the ancients up to 1800s

Diseases caused by imbalance of

4 bodily ‘humours’


4 elements



Blood, phlegm, black bile, yellow bile
Air, fire, earth and water
In relation to the 4 seasons
Treatments focused on reestablishing their balance

Purging, emesis, blistering,
bloodletting
Understanding without knowledge






Marcus Terentius Varro (in 36 BC)
‘...and because therein are bred certain minute creatures (in swamps)
which cannot be seen by the eyes, which float in the air and enter the
body through the mouth and nose and there cause serious diseases’
Ibn al-Khatib, (in 1300s, re: Bubonic Plague [Yesinia infection])
‘The fact of infection becomes clear to the investigator who notices
how he who establishes contact with the afflicted gets the disease,
whereas he who is not in contact remains safe, and how transmission
is affected through garments, vessels and earrings.’
Girolamo Fracastoro (1546)
‘… that epidemic diseases are caused by transferable seed-like entities
that can transmit infection by direct or indirect contact or even without
contact over long distances. ’
Knowledge emerges

Anton van Leeuwenhoek (1642 –
1723)


First direct observation of MOs using
a microscope
Agostino Bassi first stated the
germ theory of disease in 1835

He linked fatal muscardine disease
in silkworms to a visible fungus
JANSSEN
Edward Jenner (1749-1823)

Common empirical observation that



Benjamin Jesty (farmer) inoculated his wife and
two sons with the exudate from cowpox pustules,


Milkmaids had good complexions
They seemed to be immune to smallpox
Conferred on them immunity to smallpox during the
epidemic of 1774
Edward Jenner promoted smallpox vaccination in
1790s


Got all the credit, including a knighthood!
He had no knowledge of why vaccination was effective
Oliver Wendell-Holmes, Snr


US Poet, physician, and medical reformist
1843: published a landmark essay on the germ theory of disease 4 years
before Semmelweis




Insisted that any physician with even 1 case of puerperal fever, should:





Puerperal fever = often fatal infection contracted during or shortly after
childbirth
Transmitted from patient to patient via examining physician (iatrogenic
infection)
Cited doctors who had become ill and died after performing autopsies on
patients who had died of puerperal fever
‘Purify’ his instruments
Burn all clothing worn while assisting in the fatal delivery
Cease obstetric practice for a period of at least six months
He was vilified by the medical establishment who did not believe in
‘contagion’
He re-published his paper in 1855, to great acclaim
Ignaz Semmelweis


Worked in Vienna in 1847
Noted exceptionally high maternal mortality rate due to puerperal fever








Women were examined by medical students studying obstetrics
Students had often had prior contact with autopsy specimens
Puerperal fever was a contagious disease transmitted by cadaver material
Noted far lower morality rate for women attended by midwives
Who had not been examined by medical students
Introduced hand-washing prior to patient examination
Reduced mortality from childbirth to < 2% at his hospital
Was vilified by most of the Viennese medical establishment


(1818-1865)
His theories on the effectiveness of handwashing as effective C of I were
not accepted until Pasteur’s ‘germ theory’ was accepted
Ironically, he died of septicaemia
‘Spontaneous generation’


It was thought that corruption and rotting of organic
material was ‘self generating’, until…..
Francesco Redi (1626 – 1697) demonstrated that maggots
only grew on material that could be accessed by flies



It had been thought that maggots emerged from meat as it rotted
He showed that maggots did not appear on meat in sealed jars
Louis Pasteur demonstrated conclusively that MO growth
did not occur by spontaneous generation.


He exposed freshly boiled broth to air in vessels that was filtered to
prevent all particles passing into the growth medium
As nothing grew in the vessels, it demonstrated that MOs that
corrupted organic materials must be sourced from the exterior.
Louis Pasteur (1822 – 1895)

Formulated the ‘Germ Theory’ of disease




Formulated and proved the rabies vaccine
Named 3 methods to eliminate MOs causing wet
gangrene:



Repeated heating of food products to reduce their MO load
Quality and taste remained unaffected by process
3 of his 5 children died of typhoid


Filtration, Exposure to heat, or Exposure to chemical solutions
Invented Pasteurization (food preservation method)


Determined that MOs (‘germs’) were the cause of many diseases
Noted that MOs can grow under both aerobic and anaerobic conditions
Clean, potable water was not readily available
Would not shake hands for fear of cross infection
John Snow (1813-1858)


He used microscopy and statistics to
establish the source of an outbreak of
cholera in Soho
The Broad Street pump water was contaminated by
sewage, in 1854 (via local broken drain)




Local cases who did not contract cholera sourced their water
from another pump
But distant residents who used the Broad Street pump, did
He removed the pump handle and the epidemic reduced
He scotched the ‘miasma’ theory (‘bad air’) and helped
establish the ‘germ’ theory as the cause of
contagion


He also pioneered anaesthesia, and administered chloroform to
Queen Victoria during the birth of 2 of her children
He was TT, vegetarian, drank only boiled water, and died of a
stroke aged 45!
Florence Nightingale
(1820 – 1910)

She is best known for her work in the Crimean War (1853-56)




6/12 later a UK Sanitary Commission was sent out to Crimea



They made the sewers function, and then death rates began to fall
Nightingale still believed that the improvement was due to better food and supplies!
After the war she worked for the Royal Commission for the Health of the
Army




But death rates rose in the 1st year she was in charge of nursing at Scutari
hospital
Her methods focused on a good diet and adequate supplies, but ignored hygiene!
10x more soldiers died from typhus, typhus and cholera than from battle wounds
She was a keen statistician, and showed by statistics that:
Hygiene was paramount in the control of infection
Poor hygiene had been the cause of the majority Crimea deaths
She became a great advocate of hospital hygiene

designed the ‘X’ hospital format (clean at the centre, dirty at the periphery)
Sir Joseph Lister (1827-1912)



Prior to Lister it was generally accepted that wound
infections were desirable and arose due to ‘miasma’ (bad air)
Lister confirmed Pasteur's conclusions by his own experiments
He developed chemical antiseptics to avoid wound infections


Carbolic acid (phenol) was used to deodorize sewage, so Lister




Sprayed instruments, incisions and dressings with carbolic acid solution
Instructed surgeons to wear clean gloves and wash hands in 5% phenol
solution
Forbade porous handles on surgical instruments
Remarkable reduction in the incidence of gangrene


Heat and filtration not appropriate to human tissue
Published results in BMJ (Vol 90; 2299) 21.09.1867
Lister’s guidelines were followed to the letter during appendectomy
on Edward VII, 2 days before his planned coronation date, in June 1902



Appendectomies were notorious for post-operative infections and patient death
The King survived and was crowned in August, 1902
Lister got his gong
Joseph Bazalgette (1819–91)

~ 1845 Metropolitan Commission of Sewers ordered





Cholera epidemics of 1848-9 and 1853 killed 25,000 Londoners


1856 Bazalgette (railway builder) appointed CE of MBW
1858: the ‘great stink’: Thames was biologically dead, and putrid





all residences used cess pits
all cesspits should be closed
all residences to be connected to a system of drains and sewers
all sewers to empty into the Thames
Parliament was suspended due to the smell
Enabling Act passed to allow ‘enclosed handling’ of London sewage
1100 miles of brick-lined sewer tunnels were constructed + Pumping stations
at Deptford, Erith, Chelsea and Abbey Wood
Still just about coping with 2012 level of demands
Cholera was eradicated and there are now fish in the Thames

Unless Thames Water pumps sewage into the Oggin
Abbey Wood Pumping Station
The flush toilet



Invented by John Harrington (courtier of Elizabeth 1) in 1596
Joseph Brahma (Locksmith) improved the water closet in 1778, so that
it did not freeze up in winter (still working on I of W)
Thomas Crapper, did not invent the flush toilet, but he invented the
ballcock in 1882
Roman
communal
lavatory with
flushing
gutter
Harrington
model: there
was a flap
that opened
by a lever to
let content
drain into a
cess pit
Victorian
Flush Toilet
Koch’s 4 Postulates of
Infectious Disease (1890)

1.
2.
3.
4.
Formulated by Robert Koch and Friedrich Loeffler (1884)
Causative MO must be found in abundance in all suffering from the
disease, but should not be found in the healthy.

NB: does not recognize the carrier state or sub-clinical disease state

NB: does not apply to the prion of CJD

NB: does not apply to those with a natural immunity or to diseases that
Causative MO can be isolated from a diseased subject and grown in
pure culture
Cultured MO should cause disease when introduced into a healthy
subject.
do not affect all equally, e.g. polio
Cultured MO will be identified as identical to the original causative
MO when re-isolated from diseased experimental host
Science backs Empirical Observation 1

Pre-1850s: Sanitation/sterilization measures
and methods were known to limit the outbreak
and spread of disease.




The actual mechanism of specific infective MOs, their
vectors and
mechanisms of their transmission & biological attack,
how MOs progressed in the body at the cellular level,
and
the bio-chemical mechanism of their natural course in
the bodies of living organisms were wholly unknown.
Science backs Empirical Observation 2

By the late 1800s: Rigorous investigative
scientific methods and practices in all the
physical sciences, allowed anecdotal information
to be subject to rigorous examination.



Led to the knowledge of how living organisms receive
infection,
how living organisms manage infections once
established,
and (most important, in penicillin’s case) how natural
and man-made agents could alter the progress of
infection within the living organism
Summary






Early voices on disease prevention / infection control
were largely ignored
Pus and infection was considered an essential and
desirable part of post-surgical healing
Pasteur established the role of MOs in infection
Public health measures played the major part of
infection control in populations
Lister is credited with the introduction of aseptic
techniques during surgery
Nightingale is credited with formalization of nursing
principles and clean / dirty hospital design