This document discusses infection control concepts, including the cycle of infection and how microorganisms like bacteria, viruses, fungi and protozoa can be transmitted. It explains that hospitals are sites for disease transmission due to gathering sick patients. Proper infection control practices like following established policies are important for healthcare worker and patient safety. Microorganisms can be transmitted through direct or indirect contact via fomites, vectors, vehicles, droplets or airborne routes. The body has natural and acquired defenses against infections that can be supported by vaccines and immunoglobulins.

1. Infection control Concepts.

2. Introduction:
• As hospital are gathering places for the sick, they are also focal point
for the transmission of disease.
• Infection control key aspect in patient care.
• As a member of health care system it is a professional duty to follow
established infection control policies.
• This will promote the safety of patients, yourself and other members
of health care system.

3. Micro-organisms :
• Living organisms that are too small to be seen with naked eyes.
• Includes- bacteria , viruses , protozoa , prions and fungi.
• Normal flora – lives inside body without causing infections.
• Investigation for underlying abnormalities in specific areas of the body
when bacteria are isolated from normally sterile sites e.g. Escherichia
coli isolation from blood cultures indicates probable intra-abdominal
pathology because Escherichia coli is part of the normal gastrointestinal
flora, or isolation of a Viridans Streptococcus in blood cultures may
indicate infective endocarditis as a result of poor dentition as
Viridans Streptococcus are part of the normal mouth flora

5. Bacteria
• Bacteria are very small , single- celled organisms with a cell wall and
an atypical nucleus , that lacks a membrane .
• Cell wall is essential for survival of the bacterium , making it target for
destruction by some antibiotics.
• Bacteria grow independently and can replicate without a host cell.
• Three distinct shapes : spherical (cocci ),rod- shaped (bacilli),
and spiral (twisted).
• Can be gram positive or gram negative.
• Gram positive if they retain the color after being treated by alcohol .
• Can also be acid-fast or nonacid-fast.

6. Cont..
• Streptococci and staphylococci are gram positive. Escherichia coli is
gram negative and mycobacterium tuberculosis is acid-fast.
• Bacteria are also grouped by their oxygen requirement.
• Obligate Aerobes and anaerobes
• Bacteria that can grow in both condition either aerobic or anaerobic
are called facultative organisms .
• Some type of bacteria can generate endospores.
• Generally endospores are resistant to destruction.

7. Rickettsiae:
• Are also consider bacteria but are atypical , smaller than bacteria and
barely visible in an ordinary light microscope.
• They only grow inside animal cells (e.g. rats, rabbit)
• Do not survive in environment.
• They are transmitted among animal when they are bitten by infected
arthropods such as ticks , lice, fleas and mites.
• Human are only accidental host.
• These cause rocky mountain spotted fever and typhus fever.

8. Viruses :
• Smallest known disease – causing organisms. Must be viewed in
electronic microscope.
• A fully developed viral particle is called as virion, is made up of either
DNA or RNA.
• Is covered by protein coating called the capsid.
• Capsid may be covered by a lipoprotein envelop that has projecting
spikes .
• Enveloped viruses such as influenza , HIV , hepatitis B uses these
spike to attach to the host cell.
• Rhino virus does not posses spikes .Capsid helps in attachment.

9. Cont..
• Viruses can not survive independently.
• They invade the host cell and stimulate it to participate in the
formation of additional virus particles.
• It has been difficult to create antiviral drugs that are not also harmful
to host cell.

11. Corona virus microscopic image .

12. Fungi :
• Fungi occurs as single celled yeasts or as long, branched filament like
structures called molds (many cells).
• Yeast reproduce by forming buds, whereas mold reproduces by
spores.
• Many fungi serves for useful purpose.
• Antibiotic penicillin .
• Helps in decomposition of dead animals and plants.
• In humans fungi causes skin infections , such as athlete's foot and ring
worm.
• Respiratory infections , pharyngeal and esophageal candidiasis.

14. Prions:
• The smallest and least understood among all pathogens.
• Scientists believe that it might be a infectious protein.
• They don’t posses DNA or RNA , their method of replications are also
not fully understood.
• They affect the nerve cells and are resistant to body’s natural defense
system.
• They were first identified as the cause of scrapie, a degenerative
disease affecting the nervous system of sheep.
• Prions are the cause of bovine spongiform encephalopathy (mad cow
disease.)and both classic and variant creutzfeldt –jakob disease in
humans. Causes neurological problems and dementia.

15. Protozoa :
• They are complex single-celled animals that generally exist as free-
living organisms.
• Few are parasite and live within human body.
• May be classified as motile and non- motile.
• They locomot using pseudopods / cilia / flagella.
• Most protozoa produces some type of resistant form , such as cyst to
survive in the environment outside of host.
• Other protozoa have complex life cycles involving alternate residence
in the human body and insect vector . Like malaria.
• They can infect gastrointestinal , genitourinary , circulatory and
respiratory systems.

16. Cont..
• Amebiasis and giardiasis – causes diarrhea.
• Trichomoniasis – affects genitourinary tract. Causes yellow-greenish
discharge from male and female urethra and vagina.
• Toxoplasmosis – affects the blood and lymphatic system .

19. Cycle of Infection:
• The factor involved in the spread of disease are sometimes called the
cycle of infection.
• For infection to be transmitted , there must be an infectious organism
, a reservoir of infection , a portal of exit , a susceptible host, a portal
of entry , and a means of transporting the organism from the
reservoir to the susceptible individual .

20. Infectious Organisms:
• Microorganisms capable of causing disease are called pathogenic
organisms or pathogens.
• They posses certain properties called virulence factors.
• These factors enable bacteria to destroy or damage host cells and
resist destruction by the host’s cellular defense.
• Each bacterial pathogens has an affinity for a certain type of cell in
the body.
• They attach to this cell and excrete protein substance called toxins.
• Virulence factor assist the pathogens to avoid recognition by the host
cells .

21. Reservoir Of Infection:
• The reservoir or source of infection may be any place where
pathogens can thrive in sufficient numbers to pose a threat.
• Such environments must provide moisture, nutrients , and a suitable
temperature , all of which are found in human body.
• A reservoir of infection might be a patient with hepatitis , a
radiographer with an upper respiratory infection or a visitor with
staphylococcal boils.
• Animals , the reservoir for salmonella.
• Soil , the reservoir for tetanus.
• Food, the reservoir for botulinum.
• Water, the reservoir for typhus.

22. Portal of Exit:
• The portal or exit from the human body may be any route through
which blood, body fluid , excretions, or secretions.
• Example includes the respiratory , urinary and gastrointestinal tracts ,
an infected wound and the bloodstream .

23. Susceptible host :
• Patient who have a reduced natural resistance to infection.
• May develop nosocomial infection.
• For health care workers – occupationally acquired infections.-
hepatitis B and C viruses are the biggest concern.
• Hospital workers , mainly radiographer are exposed to many
pathogens.

24. Portal of Entry:
• It is the route by which microorganisms gain access into the
susceptible host.
• Example: respiratory , urinary and GI tracts, open wound or break in
skin , mucous membranes of eyes, nose and mouth and the blood
stream .

25. Transmission of Disease.
• Direct contact
• Indirect contact
a) Fomites- object that has been in contact with pathogenic organisms
is called a fomite. A contaminated urinary catheter is a typical
example. X-ray table , vertical Bucky , sponges etc.
b) Vectors – vector is an arthropod / insect (infected by infectious
organisms ). Eg: malaria , dengue , plague etc.
c) Vehicles – any medium that transport microorganisms like food,
water , drugs, blood etc.
d) Droplet contamination – Large droplet containing microorganism
and measuring more than 5 micrometer. Does not last in air form
long time and travel short distance around 3 feet . Eg: Influenza,
meningitis , diphtheria , pertussis , streptococcal pneumonia etc.

26. Cont..
e) Airborne Transmission – occurs from dust that contains spores or
droplet nuclei.
- Droplet nuclei are defined as particle of evaporated droplets
containing microorganisms.
- They can remain suspended in air for longer period of time.
- Eg: Tuberculosis , rubeola (Measles), Varicella viruses.

27. Body’s defense against Infections:
• Natural Resistance- intact skin and mucous membranes , cilia of
respiratory tract , lysozyme in tears , acid in stomach , vagina and skin
. 2nd line of defense is inflammatory response and phagocytosis .
Viruses infected cells produce interferons , a small protein molecule
that protects the uninfected cells from invasion by the original virus
as well as others. Produced in labs. for treatment of hepatitis B and C.

28. Acquired Immunity :
• Humans are born with a certain amount of immunity , but most
humans become resistant to disease by becoming infected with a
specific organism.
• Immunity can also be conferred from vaccines made from dead or
weakened strains of microorganisms for a specific infection. –
Acquired Immunity .
• Antibodies are produced against antigens .
• Acquired immunity is long term .

29. Passive Immunity:
• Passive immunity occurs when an individual receives preformed
antibodies from others to provide temporary immunity .
• Eg: immunoglobulin injections to prevent infection after exposure to
certain viruses and the immunity that is passed to infants from their
mothers at birth and in breast milk .

30. • Reference: Patient care in Radiography , 9th edition , Ruth Ann Ehrlich
.
• Online sources.
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