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Flashcards in Infection Control Deck (71)
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Pathogenicity :

the ability to cause disease



the degree of pathogenicity


Nonspecific Defense Mechanisms:

defense that protect us from any pathogen


Specific Defense Mechanism (immune response) :

defense that the body offers against a particular pathogen



Microorganisms that occur in specific environments such as: the intestine, skin , vagina and oral cavity


Two types of flora

Resident or normal Flora-always present
Transient flora- occur in periods of limited duration-e.g. Staph aureus


Six Links in the chain of infection

Infectious or causative agent
Portal of exit
Mode of transmission
Portal of entry
Susceptible host


Infectious /Causitive Agent:

1st link in chain of infection
An pathogen or disease producing micro-organism that invades the host and causes disease

Biological agent- living organism invade the host

Other agents
Chemical agent-substance that interact with the body e.g. pesticides, food additives, medications and industrial chemicals
Physical agent- environmental factors such as heat, light, noise and radiation


The Reservoir

2nd link in chain of infection
Place where the agent can survive , grow and multiply e.g. humans , animals and environmental surfaces
The reservoir must contain oxygen and organic matter in order for the host to grow
Must have proper temperature, Ph level, light and moisture for growth
Most common reservoirs are human, animals, the environment
Fomites - objects such as surgical instrument and laboratory instruments
Humans can be carriers or infectious agents


Human reservoirs.

Many common infectious diseases have human reservoirs.
Diseases that are transmitted from person to person without intermediaries include the sexually transmitted diseases, measles, mumps, streptococcal infection, and many respiratory pathogens.


Asymptomatic or passive or healthy carriers:

Human reservoir
never experience symptoms despite being infected.


Incubatory carriers:

Human reservoir
can transmit the agent during the incubation period before clinical illness begins.


Convalescent carriers :

Human reservoir
those who have recovered from their illness but remain capable of transmitting to others.


Chronic carriers

Human reservoir
are those who continue to harbor a pathogen such as hepatitis B virus


Animal reservoirs. 

Humans are also subject to diseases that have animal reservoirs.
Diseases are transmitted from animal to animal, with humans as incidental hosts.
Example : brucellosis (cows and pigs), anthrax (sheep), plague (rodents), trichinellosis/trichinosis (swine), tularemia (rabbits), and rabies (bats, raccoons, dogs, and other mammals),West Nile encephalitis (birds)


Environmental reservoirs

Plants, soil, and water in the environment are also reservoirs for some infectious agents.
Many fungal agents, such as those that cause histoplasmosis, live and multiply in the soil.
Outbreaks of Legionnaires disease are often traced to water supplies in cooling towers and evaporative condensers, reservoirs for the causative organism Legionella pneumophila


Port of Exit

The path by which a pathogen leaves its host.
The portal of exit usually corresponds to the site where the pathogen is localized. For example:
Influenza viruses and Mycobacterium tuberculosis : exit the respiratory tract, schistosomes through urine, cholera vibrios in feces
Blood borne agents: can exit by crossing the placenta from mother to fetus (rubella, syphilis, toxoplasmosis)
Blood borne Pathogens: others exit through cuts or needles in the skin (hepatitis B) or blood-sucking arthropods (malaria).


Modes of Transmission

An infectious agent may be transmitted from its natural reservoir to a susceptible host in different ways


Direct transmission-

Direct contact
Droplet spread


Indirect transmission-

Vectorborne (mechanical or biologic)


Contact transmission-

Mode of Transmission- Direct
transfer of an agent from an infected person to a non infected person e.g. colds, Std'st
Occurs through skin-to-skin contact, kissing, and sexual intercourse.
Most frequent source of health care associated infections e.g. phlebotomist not changing gloves and washing hands before taking blood from the next patient


Droplet Transmission

Mode of Transmission- Direct
Form of contact but method of transfer is different (droplets propelled up to 3 feet- not suspended in the air)
Enters susceptible host trough the nasal mucosa, the mouth or conjunctiva of the eye
Example : Pertussis , influenza and meningococcal infection
Technician handling blood or body fluid


Airborne Transmission-

Mode of Transmission-Indirect
When a susceptible person contacts contaminated droplets or dust particles in the air e.g measles and anthrax spores(Particles distributed by air current)
Aerosols- created when removing
caps from tubes of blood, urine or other body fluid


Vehicle Transmission-

Mode of Transmission-Indirect
agent transferred by inanimate objects e.g. water , food , drugs and equipment
The inanimate object becomes a vehicle when it is touched or injected by a susceptible host
Technician: soiled lab coats must be disposed of properly
Soiled lab equipment must be disinfected


Vectorborne transmission-

Mode of Transmission-Indirect
Occurs when a living host e.g. mosquitoes, fleas, ticks, lice and other animals comes in contact with contaminated items, food, linen–
The animal or insect becomes the vector that transmits disease to the susceptible host. e.g Lyme disease (bite of deer ticks)


Portal of Entry

Blood (hepatitis B, human immunodeficiency virus)


Respiratory tract-

Portal of Entry
mucus droplets



Portal of Entry
from mother to foetus via the placenta or umbilical cord


Circulatory system

Portal of Entry
through insect or rodent bites


GI tract(orifices)-

Portal of Entry
ingestion of contaminated food or water