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Infection Control

THE CHAIN OF INFECTION
Infectious diseases are spread through a series of steps known as the “chain of infection”.
For an infection to occur and spread, each of the six links of the chain must take place.
Removing any link in the chain will stop the cycle. Therefore, identifying and instituting appropriate actions at different steps in the cycle will halt the spread of the infection.
1. Infectious Agent
Infectious agents can be:
Bacteria (one-celled microorganisms), examples of disease: gonorrhea, tuberculosis, strep throat;
Viruses (one-celled microorganisms that contain either DNA or RNA but not both), examples of disease: influenza, measles, hepatitis B;
Parasites (single or multi-celled microorganisms), examples of disease: malaria, pinworm, lice;
Fungi (molds and yeasts), examples of disease: vaginal yeast infections, ringworm, histoplasmosis;
Rickettsia (single or multi-celled microorganisms that occupy a position intermediate between viruses and bacteria), examples of disease: Rocky Mountain Spotted Fever, typhus, Lyme Disease; and
Prions (a small infectious particle composed primarily of protein), example of disease: Creutzfeld-Jakob Disease.
2. Reservoir
A reservoir is a place for microorganisms to live. Reservoirs can be animals, insects, food, water, humans, objects, the air we breathe, etc.
If a human, animal, or insect serves as the reservoir, they often do not have any symptoms of the disease.
3. Portal of Exit
There must be a way for the microorganism to leave the reservoir for transmission of disease. This is known as the portal of exit.
For example, some infectious bacteria may leave the human body in feces.
4. Method/Mode of Infection
Infectious diseases are spread by contact, by vehicle, by vector, and by inhalation.
Transmission by Contact
Direct contact
Some microorganisms are transferred from one individual to another by close or intimate contact such as kissing.
Example: hepatitis A, staph/strep infections, scabies
Indirect contact
Some microorganisms are transferred from one individual to another when the healthy individual comes in contact with items from the infected individual such as eating utensils, Kleenex, contaminated clothing, bed linens, contaminated sharps (needles and instrument probes), and splashes of blood, serum, plasma, body fluids to the eyes, mouth, or nose.
Includes transfer of microorganisms through needle sticks and sharps injuries.
Examples: hepatitis A, hepatitis B, hepatitis C, HIV, influenza, staph/strep infections.
Droplet contact
Microorganisms are present in droplets generated when an infected individual coughs, sneezes, or talks. The healthy individual becomes infected when these droplets come in contact with nose, mouth, or eyes.
Requires close contact (within 3 feet); droplets are > 5 microns in size.
Examples: chickenpox, influenza, respiratory syncytial virus, measles.
Transmission by Vehicle
Infection is transmitted by contaminated food, water, and drugs.
Examples: E. coli 0157-contaminated food/drink, chicken/utensils contaminated with salmonella.
Transmission by Vector
Infection transmitted by an insect, animal, arthropod.
Examples: West Nile virus (mosquito), malaria (mosquito), Lyme disease (tick).
Transmission by Inhalation
Microorganisms are present in droplets generated when an infected individual coughs, sneezes, spits, laughs, or talks.
Infection is transmitted when a healthy individual inhales the droplets.
Droplets, called droplet nuclei, are < 5 microns in size and can remain suspended in air, be widely dispersed by air currents, and remain in air over a long distance.
Close patient contact is not necessary.
Example: tuberculosis.
5. Portal of Entry
Microorganisms must have a means of entering a new reservoir or host.
Microorganisms can enter through breaks in the skin, through the mucous membranes, through the digestive tract, through an insect bite, through the respiratory tract, etc.
6. Susceptible Host
If the host’s immune mechanisms are strong, it may be able to stop the infection. However, factors such as age, genetics, nutritional status, disease state, and overall health, can make a person significantly more susceptible to a microorganism.
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