For Nursing Students

1. Infection- Microbiology
Mrs. Royce Mathew

2. • Infection- it is an invasion of body tissue
by microorganisms and their growth
there.
• Such microorganism is called- an
infectious agent
• If the microorganism produces no
evidence of infection- asymptomatic or
sub clinical
• A detectable alteration in normal tissue
function - disease

3. • Infection- The invasion and multiplication of
microorganisms such as bacteria, viruses, and
parasites that are not normally present within
the body.
• infection and immunity involve interaction
between the animal body (host) and the
infecting micro organism.
• Based on their relationship to their hosts:
microorganisms can be classified as
saprophytes and parasites.

4. • Saprophytes are free-living microbes that
subsist on dead or decaying organic matter.
• They are found in soil and water and play an
important role in the degradation of organic
materials in nature.
• They are generally incapable of multiplying on
living tissues and therefore are of little
relevance in infectious disease.
• Exceptionally, however, some saprophytes like
B.subtilis may infect devitalised hosts whose
natural resistance is greatly reduced
(opportunistic infection).

5. Parasites are microbes that can establish
themselves and multiply in hosts. Parasitic
microbes may be either pathogens or
commensals
• Pathogens are microorganisms that are
capable of producing disease in the host.
• Commensal microbes live in complete
harmony with the host without causing any
damage to it. The normal bacterial flora of the
body consist largely of commensals.

6. CLASSIFICATION OF INFECTIONS
Infections may be classified in various ways.
• Initial infection with a parasite in a host is
termed primary infection.
• Subsequent infections by the same parasite in
the host are termed re-infection
• When a new parasite sets up an infection in a
host whose resistance is lowered by a pre-
existing infectious disease this is termed
secondary infection .

7. • Focal infection (more appropriately focal
sepsis) indicates a condition where, due to
infection or sepsis at localised sites such as the
appendix or tonsils, generalised effects are
produced.
• When in a patient already suffering from a
disease a new infection is set up from another
host or another external source, it is termed
cross-infection.
• Cross-infections occurring in hospitals are
called nosocomial infections (from Greek
nosocomion or hospital)- Hospital acquired
Infection HAI

8. • The term iatrogenic infection refers to
physician induced infections resulting from
investigative, therapeutic or other procedures.
• Depending on whether the source of infection
is within or outside the host's own body,
infections are classified as endogenous or
exogenous, respectively.

9. Based on the clinical effects of infections, they
may be classified into different varieties.
• Inapparent infection is one where the clinical
effects are not apparent. The term subclinical
infection is often used as a synonym.
• Atypical infection is one in which the typical or
characteristic clinical manifestations of the
particular infectious disease are not present.
• Latent infection is one in which some
parasites, following infection, may remain in
the tissues in a latent or hidden form,
proliferating and producing clinical disease
when the host resistance is lowered

10. SOURCES OF INFECTION
1. Humans: The commonest source of infection
in humans are humans themselves.
• The parasite may originate from a patient or a
carrier.
• A carrier is a person who harbours the
pathogenic microorganism without suffering
any ill effect because of it.
• Several types of carriers have been identified

11. • A healthy carrier is one who harbours the
pathogen but has never suffered from the
disease caused by the pathogen, while a
convalescent carrier is one who has recovered
from the disease and continues to harbour the
pathogen in his body.
• Depending on the duration of carriage,
carriers are classified as temporary and
chronic.
• The temporary carrier state lasts less than six
months, while chronic carrier stage may last
for several years and sometimes even for the
rest of one's life

12. • The term contact carrier is applied to a person
who acquires the pathogen from a patient, while
the term paradoxical carrier refers to a carrier
who acquires the pathogen from another carrier.
• The incubation period is the time between
exposure to an infectious agent and the
development of symptoms.
• Different infectious agents have different
incubation periods.
– For example, the incubation period for HIV can be a
few months to many years. For the common cold
virus, symptoms usually appear 1 to 2 days after
exposure.

13. 2. Animals: Many pathogens are able to infect
both human beings and animals.
• Animals may, therefore, act as sources of
human infection.
• In some instances, the infection in animals
may be asymptomatic.
• Such animals serve to maintain the parasite in
nature and act as the reservoir of human
infections.
• They are, therefore, called reservoir hosts.

14. • Infectious diseases transmitted from animals
to human beings are called zoonoses.
Zoonotic diseases may be
• bacterial (plague from rats),
• viral (rabies from dogs),
• protozoal (toxoplasmosis from cats),
• helminthic (hydatid disease from dogs) or
• fungal (zoophilic dermatophytes from cats and
dogs).

15. 3. Insects: Blood sucking insects may transmit
pathogens to human beings.
• The diseases so caused are called arthropod-
borne diseases.
• Insects such as mosquitoes, ticks, mites, flies,
fleas and lice that transmit infections are
called vectors.
• Transmission may be mechanical (for example,
transmission of dysentery or typhoid bacilli by
the domestic fly). Such vectors are called
mechanical vectors.

16. • In other instances, the pathogen multiplies in the
body of the vector, often undergoing part of its
developmental cycle in it. Such vectors are
termed biological vectors (for example, Aedes
aegypti mosquito in yellow fever, Anopheles
mosquito in malaria).
• Biological vectors transmit infection only after
the pathogen has multiplied in them sufficiently
or has undergone a developmental cycle.
• The interval between the time of entry of the
pathogen into the vector and the vector
becoming infective is called the extrinsic
incubation period.

17. 4. Soil and water: Some pathogens can survive in
the soil for very long periods.
• Spores of tetanus bacilli may remain viable in the
soil for several decades and serve as the source of
infection.
• Fungi (Histoplasma capsulatum, Nocardia
asteroides) and parasites such as roundworm and
hookworm survive in the soil and cause human
infection.
• Water may act as the source of infection either
due to contamination with pathogenic
microorganisms (cholera vibrio, infective hepatitis
virus) or due to the presence of aquatic vectors
(cyclops in guineaworm infection).

18. 5. Food: Contaminated food may act as a source
of infection.
• The presence of pathogens in food may be due
to external contamination (food poisoning by
staphylococcus) or pre-existent infection in
meat or other animal products (salmonellosis).

19. METHODS OF TRANSMISSION OF INFECTION
1. Contact: Infection may be acquired by
contact, which may be direct or indirect.
• Sexually transmitted diseases such as syphilis
and gonorrhea illustrate spread by direct
contact.
• The term contagious disease had been used
for diseases transmitted by direct contact,
distinct from infectious disease, signifying all
other modes of transmission

20. • Indirect contact may be through the agency of
fomites, which are inanimate objects such as
clothing, pencils or toys which may be
contaminated by a pathogen from one person
and act as a vehicle for its transmission to
another.
• Pencils shared by school children may act as
fomites in the transmission of diphtheria, and
face towels in trachoma.

21. 2. Inhalation: Respiratory infections such as
influenza and tuberculosis are transmitted by
inhalation of the pathogen.
• Such microbes are shed by the patients into the
environment, in secretions from the nose or
throat during sneezing, speaking or coughing.
Large drops of such secretions fall to the ground
and dry there.
• Pathogens resistant to drying may remain viable
in the dust and act as sources of infection.
• Small droplets, under 0.1 mm in diameter,
evaporate immediately to become minute
particles or droplet nuclei (usually 1-10 µmin
diameter) which remain suspended in the air for
long periods, acting as sources of infection

22. 3. Ingestion: Intestinal infections are generally
acquired by the ingestion of food or drink
contaminated by pathogens.
• Infection transmitted by ingestion may be
waterborne (cholera), food borne (food
poisoning) or hand borne (dysentery).
• The importance of finger borne transmission
is being increasingly recognized, not only n the
case of pathogens entering through the
mouth, but also those that enter through the
nose and eyes.

23. 4. Inoculation: Pathogens, in some instances, may
be inoculated directly into the tissues of the host.
• Tetanus spores implanted in deep wounds, rabies
virus deposited subcutaneously by dog bite and
arboviruses injected by insect vectors are
examples.
• Infection by inoculation may be iatrogenic when
unsterile syringes and surgical equipment are
employed.
• Hepatitis B and the human immunodeficiency
virus (HIV) may be transmitted through
transfusion of infected blood, or the use of
contaminated syringes and needles, particularly
among addicts of injectable drugs

24. 5. Insects: Insects may act as mechanical or
biological · vectors of infectious diseases.
6. Congenital: Some pathogens are able to cross
the placental barrier and infect the fetus in utero.
This is known as vertical transmission.
• This may result in abortion, miscarriage or
stillbirth.
• Live infants may be born with manifestations of a
disease, as in congenital syphilis.
• Intrauterine infection with the rubella virus,
especially in the first trimester of pregnancy, may
interfere with organogenesis and lead to
congenital malformations.
• Such infections are known as teratogenic
infections.

25. 7. Iatrogenic and laboratory infections:
• Infection may sometimes be transmitted
during administration of injections, lumbar
puncture and catheterisation, if meticulous
care in asepsis is lacking.
• Modern methods of treatment such as
exchange transfusion, dialysis and organ
transplant surgery have increased the
possibilities for iatrogenic infections.
• Laboratory personnel handling infectious
material are at risk and special care should be
taken to prevent laboratory infection.

26. • The outcome of an infection will depend on
the interaction between microbial factors
which predispose to pathogenicity and host
factors which contribute to resistance.

27. FACTORS PREDISPOSING TO MICROBIAL
PATHOGENICITY
• The terms 'pathogenicity' and 'virulence' refer
to the ability of a microbe to produce a
disease or tissue injury but it is important to
make a distinction between them.
• Pathogenicity is generally employed to refer
to the ability of a microbial species to produce
disease, while term virulence is applied to the
same property in a strain of microorganism.

28. • Virulence- ability to produce disease
• Communicable disease- An illness due to a
specific infectious agent that arises through
transmission of that agent from an infected
person, animal, or inanimate reservoir to a
susceptible host. (Synonym: infectious
disease.)
• Pathogen or causative agent- A biologic agent
(organism) capable of causing disease. These
include bacteria, viruses, fungi, and protozoa.
Sometimes collectively referred to as “germs.”

29. • Pathogenecity- it is the ability to produce disease.
– A true pathogen causes diseases or infection in healthy
individual.
– An opportunistic pathogen causes disease only in a
susceptible individual.
– Infectious diseases are a major cause of death world wide.
– The control of the spread of microorganisms and protection
of people from communicable disease and infections are
carried out on international, national, state , community
and individual level.
– WHO is the major regulatory agency at the international
level.
– At the state level the health departments track the
epidemics and illness as reports are made throughout that
area.

30. • Causative Agents/OrganismsSynonyms:
pathogen, infectious agent, etiologic agent.
– The pathogens that cause infections are
microorganisms.
– Bacteria, viruses, fungi, and protozoa (“germs”)
are very common in the environment, and most of
them are harmless or even beneficial to people.
– Creating an environment with no microorganisms
is not a realistic goal outside of highly specialized
laboratories.

31. • Most pathogens require an “infectious dose” to
cause disease; that is, it usually takes thousands to
cause disease, not just one or two.
• Pathogens also vary in infectivity (how easy they are
for someone to “catch”) and virulence (the level of
danger from the infection they cause).
• Patients in healthcare settings are generally more
susceptible to infection due to underlying illness and
other factors that weaken their resistance to
infection.
• Therefore, a key goal of infection control programs is
to reduce the number of infectious microbes in
healthcare settings through hygienic practices such
as hand washing and environmental cleaning.

32. Portal of Exit
• The portal of exit is the route (or routes) by which
the causative agent gets out of the reservoir.
• In human reservoirs, skin is an important portal
of exit.
– Breaks in the skin such as sores, wounds, and cuts
may be the portal of exit of infectious microbes, but
germs may exit the host from intact skin as well.
– MRSA and Streptococcus are potent germs that live on
skin and thus can easily exit their reservoir.
– Any body fluid or matter may carry microorganisms
out of the body.
– Blood, faeces, respiratory secretions, and nasal
exudates are examples of body fluids and matter that
enable pathogens to exit the body.

33. • Body fluids and matter from various body
systems are important sources of infection in
healthcare settings.
• Examples of portals of exit from the human
body include:
– Respiratory tract
– Gastrointestinal (or alimentary) tract
– Skin
– Genitourinary tract
– Circulatory system (e.g., blood)

34. • Medical treatments and procedures and
illnesses often increase the opportunities for
organisms to exit the body, thereby increasing
exposure to infectious agents.
• A common example of this is blood drawing,
which allows blood borne pathogens to exit
the circulatory system of the reservoir.
• Diarrheal disease caused by prolonged
treatment with antibiotics is an example of an
illness that increases exit of pathogens from
the GI tract.

35. Modes of Transmission
• In order for an organism to get from
one person to another or from one
place in the body to another, it must
have a way of getting there, or a mode
of transmission.
• For any single agent, there are often
many different ways it can be
transmitted.

36. Portals of Entry
• The term portal of entry refers to the
anatomical route (or routes) by which an
infectious organism gains entry to a
susceptible host.
• The portal of entry is often the same as
the portal of exit from the reservoir but
may include other portals of entry as
well.

37. • For example, the flu virus exits the respiratory tract
when a person sneezes and enters the respiratory
tract of a new host who inhales the infectious virus
released into the air.
– Flu viruses can also exit the body when a person blows his
or her nose in a tissue.
– If another person touches the contaminated tissue and then
touches his nose, the portal of exit from the reservoir and
the portal of entrance is the same.
• However, sometimes the exit and entry portals are
different.
– For example, staph bacteria may escape one person’s
respiratory tract or nose to infect another person’s skin.
– Or a wound infected with MRSA may infect another
person’s nasal passage.
– E. coli, hepatitis A, and many other microbes exit the bowel
in feces and infect a new host via the oral route.

38. Susceptible Host
• The final link in the chain of infection is the
susceptible host.
• Susceptibility can be reduced in several ways. For
some diseases, there are effective vaccines.
• Other diseases produce lasting immunity after
illness.
• People have better resistance to disease when they
are well rested, well fed, and relatively stress free.
• People who have healthy immune systems are often
able to resist infection even when microorganisms
do invade.
• Host factors that influence the outcome of an
exposure include the presence or absence of natural
barriers, the functional state of the immune system,
and the presence or absence of an invasive device.

39. • Course of infection
–Incubation period
–Prodormal Stage
–Illness stage
–Convalescence stage

40. • Incubation period- interval between
entrance of pathogen into body and
appearance of first symptom. E.g.
Chicken pox- 2-3 weeks, common cold 1-
2 days
• Prodromal stage- Interval from the onset
of non specific signs and symptoms(
malaise, low grade fever) to more
specific symptoms. Microorganism grows
and patient is more capable of spreading
disease to others.

41. • Illness stage- period when the patient
manifests signs and symptoms specific to
the type of infection. E.g. common cold
manifested by sore throat, rhinitis, sinus
congestion
• Convalescence stage- interval between
the disappearance of acute symptoms of
an infection to the complete recovery. It
may take several days to months.

42. • Risk factors of infection-
– Broken skin mucosa
– Traumatized tissue
– Decreased ciliary action
– Altered peristalsis
– Obstructed urine flow
– Change in the pH of secretions
– Reduced hemoglobin level
– Suppression of WBC
– Suppresed inflammatory response
– Thinner dermal and epidermal layer of the skin decreases sweat
and skin elasticity
– Circulatory or congestive heart disease
– Reduced elasticity of the veins, blood pooling in lower
extremities
– Dehydration, loss of saliva production
– Loss of ability to secreate HCl I stomach
– Protein and calorie mal nutrition, vitamin deficiency
– Drug therapy like corticosteroid, cytotoxic drugs
– Exposure to nosocomial infection

43. • Breaking the chain of infection.
– 1. Control or elimination of infectious agent.
• Proper hand washing with soap and water. Disinfect the
articles used for the patients.
• Sterilization of contaminated objects, sterilization and
disinfection are physical processes, involving the use of
heat, radiation and chemical process.
• Bathing with soap and water to remove secretion,
drainage, perspiration.
• Frequent change of dressing. Proper disposal of waste and
contaminated articles.
• Disposal of contaminated needles and syringes in moisture
– resistant, puncture proof containers.
• Keep the patients bedside unit neat and clean.
• Bottled solutions should be placed with tight caps as per
instructions.

44. 2. control of portal of exit.
• Practice aseptic precautions.
• Avoid talking directly into another person’s
face to prevent droplet infections.
• Wearing of masks is important once the nurse
herself has infection or deals with patients
suffering from infections.
• Careful handling of wastes like urine, feces,
emesis and blood is important.
• Disposable gloves should be worn to prevent
direct contact with wastes or infected
materials

45. 3. control of transmission of infection.
• Discourage sharing bedpan, urinals, basins etc..
• Use individual thermometer for the patients.
• Damp dusting should be done to prevent
scattering of dust in air.
• Protect own clothing from contact with infected
materials.
• Practice hand washing technique. This is
recommended in the following situations
– Before contact with patients who are susceptible to
infection.
– Before performing invasive procedures like
administration of injections, suction.
– Before and after dressing or touching open wounds.
After handling contaminated equipment.
– Between contact with different patients in high risk
units

46. Control of portal of entry.
• Maintain integrity of skin and mucus membranes. Proper
positioning of tubing prevents injuries and skin
breakdown.
• Regular skin care is essential with application of lubricants.
• Turning and positioning of debilitated patients will help in
preventing skin break down.
• Ensure the personal hygiene of the patients regularly.
• Dispose of contaminated syringes and needles to prevent
accidental injuries to hospital personnel as well as
patients.
• Proper handling of the drainages, catheters is essential.
• Care should be while collecting and handling specimens.
• Regular wound care is to be instituted properly to prevent
infection

47. Protection of susceptible host.
• This involves protecting normal defense
mechanism by .
• Regular bathing along with adequate
lubrication of the skin.
• Regular oral hygiene.
• Maintaining an adequate fluid intake.
• Encouraging deep breathing and coughing
exercises.
• Providing immunization to children and adults

48. Chain of infection