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Unit 12
Infection
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Objectives
• Spell and define terms.
• Identify the most common microbes and
describe some of their characteristics.
• List the links in the chain of infection.
• List the ways that infectious diseases
are spread.
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Objectives
• Define spores and explain how spores
differ from other pathogens.
• Name five serious infectious diseases.
• Identify the causes of several important
infectious diseases.
• Describe common treatments for
infectious disease.
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Objectives
• List natural body defenses against
infections.
• Explain why patients are at risk for
infections.
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Introduction
• Humans are surrounded by a world of
tiny organisms
• These beings cannot be seen with the
naked eye
• They make their presence known only
by their effects
– Same way we become aware of the wind
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Microbes
• There are many different types of
microbes
– Many of which are pathogenic to humans
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Bacteria
• Simple one-celled microbes
• Named according to their shapes and
arrangement
• Cause infections in the skin, respiratory
tract, urinary tract, and bloodstream
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Fungi
• Two groups of fungi are most commonly
associated with infection in humans
– Yeasts
– Molds
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Viruses
• Smallest microbe
• Has a variety of shapes
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Protozoa
• Simple one-celled organisms
• Live on living matter
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The Chain of Infection
• Infections occur when certain conditions
exist
• Conditions are called the chain of
infection
• Refer to Figure 12-3A
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The Chain of Infection
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Chain of Infection
• Breaking one link in the chain of
infection is all that is needed to prevent
the spread of disease
• Refer to Figure 12-3B
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Chain of Infection
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Causative Agent
• Microorganism that can produce the
disease process in humans
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Susceptible Host
• Person who can become infected with a
pathogen
• Unable to resist a microorganism
invading the body, multiplying, and
causing infection
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Susceptible Host
• Host is susceptible to the disease
– Lacks immunity or physical resistance to
overcome the invasion of pathogens
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Reservoir
• Where pathogens live, multiply, and
survive
• May or may not multiply in the reservoir
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Reservoir
• Source
– Person, animal, or substance from which
the infectious agent passes to the host
– May also be an inanimate object, such as
water, a sink or counter top, or doorknob
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Source
• Reservoir may be the same as the
source or different from the source
– Reservoir is where the pathogen lives or
resides
– Source is the site from which the pathogen
is transmitted to a susceptible host
• Directly or indirectly through an object or in the
environment
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Source
• This distinction is important when
deciding the types of precautions and
control measures to use to prevent
further spread
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Portals of Entry
• Where organisms enter the body are
called portals of entry
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Portals of Entry
• Portals
– Body openings, mucous membranes, and
breaks in the skin
• Portals also result from tubes placed in
body
– Urinary catheters, or from punctures
produced by invasive procedures such as
intravenous fluids
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Portals of Exit
• Infectious organisms leave the reservoir
of the human host through body
secretions or portals of exit
• Portal provides a way for a pathogen to
leave the reservoir
– Leaving nose or mouth on a sneeze or
cough
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Mode of Transmission
• Mode or method of transmission:
– Method by which the infectious agent
passes from a source to the host
– May be transmitted by more than one route
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Mode of Transmission
• Methods of transmission are:
– Direct contact
– Indirect contact
– Airborne and droplet spread
– Fomites (a method of indirect contact)
– Vectors
– Common vehicles
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Types of Infections
• Infections can be:
– Local
– Generalized
– Systemic
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Body Flora
• Different microbes live on our body
surfaces
– Microbes are called the normal body flora
– Flora are not the same in all body areas
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Body Flora
• They are not harmful in the area in
which they normally reside
– But may cause infection if they are moved
to another area of the body
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How Pathogens
Affect the Body
• Potential for infection depends on the
risk factors listed previously
• Two major factors are:
– Susceptibility of the host
– Amount of infectious agent that finds a
portal of entry into the host
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Body Defenses
• The body has some natural defenses to
protect itself from infections
• There are several natural external
defenses
• The most important of these is the skin
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Immunity
• Immunity is the ability to fight off
disease caused by microbes
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Immunizations
• Artificial defenses called immunizations
protect against specific pathogens
• Immunization is provided by vaccines
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Immunosuppression
• Occurs when the body’s immune
system is inadequate
– Fails to respond to the challenge of
infectious disease organisms that it
normally would fight successfully
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Serious Infections
in Health Care Facilities
• Serious bacterial and viral infections are
increasing in health care facilities as
well as in the general public
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Bacterial Infections
• Bacteria are often the cause of serious
skin, respiratory, urinary, and
gastrointestinal infections in patients
• If a physician suspects that a patient
has a bacterial infection:
– Culture and sensitivity test may be ordered
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MRSA and VRE
• Two groups of organisms have become
resistant to two powerful antibiotics
– Methicillin and vancomycin
• These organisms are:
– Methicillin-resistant Staphylococcus aureus
(MRSA)
– Vancomycin-resistant enterococci (VRE)
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Tuberculosis
• Before the development of antibiotics:
– Tuberculosis was a widespread disease
with a high fatality rate
• In the 1950s:
– Use of antibiotics effective against
tuberculosis caused deaths to drop sharply
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Escherichia Coli 0157:H7
• You have learned that Escherichia coli
can cause serious problems outside the
intestinal tract.
• E. coli 0157:H7
– Caused outbreaks resulting in serious
illness and death
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Pseudomembranous Colitis
• Many bacteria live in the bowel of a
healthy person
• Most of them are harmless
– Some friendly bacteria help with digestion
• A few of these have the potential to be
troublemakers if they get out of control
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Viral Infections
• Viral infections include:
– Shingles
– Influenza
– Hepatitis
– Acquired immune deficiency syndrome
(AIDS)
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Other Important Infections
• Infection caused by fungi:
– Coccidioidomycosis
• Infection caused by protozoa:
– Giardiasis
– Cryptosporidiosis
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Spores
• Microscopic reproductive bodies are
responsible for the spread of some
diseases
• They can survive in a dormant form until
conditions are ideal for reproduction
• Spores will multiply and continue to
spread infection
• They are very difficult to eliminate
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Spores
• Avoid alcohol products for cleansing
hands if a patient has a disease spread
by spores:
– Alcohol will not kill spores
– Mechanical action of washing with soap
and water loosens spores and washes
them down the drain
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Severe Acute
Respiratory Syndrome
• SARS is a highly contagious viral
respiratory illness caused by a
coronavirus
• Special isolation precautions are
required
• Much remains to be learned about
SARS
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Parasites
• Survive by feeding off another human or
animal
– Head lice are parasites that spread by
direct and indirect contact
– Scabies is a skin disease caused by a
parasite called a mite
– Mites are microscopic organisms that
cannot be seen with the eye
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Parasites
• Both head lice and scabies are known
for spreading rapidly through health
care facilities
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Bedbugs
• Are real parasites
– Most people believe they are imaginary
– Survive in hot and cold environments and
live up to a year without eating
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Bedbugs
• There is no recorded incidence of
disease as a result of bedbugs,
although it is suspected
• Bites cause a painful rash on the skin
• Bedbugs feed at night
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Bedbugs
• Bedbugs hide in or around the bed,
including:
– In the mattress
– Behind the headboard
– Behind the baseboard on the wall
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Bioterrorism
• Use of biological agents
– Pathogenic organisms or agricultural pests,
for terrorist purposes
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Smallpox
• Smallpox is a serious viral infection that
is sometimes fatal
• Disease emerged thousands of years
ago but was eliminated during the
twentieth century
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Outbreak of Infectious
Disease in a Health Care Facility
• An outbreak of an infection in a health
care facility can be serious for all
patients
• Unless steps are taken immediately
– Infection can spread rapidly
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