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Six Elements of Infection

There are six elements in the cycle of infection, and all six must be present before the transmission of infection can take place.

Element in the cycle of infection Explanation Common examples
1. Infectious Agent When germs enter the body, they can cause illness
  • Bacteria, virus, fungi, protozoa
2. Reservoir Where germs normally live and multiply
  • Humans
  • Contaminated food, water, toys, sports equipment
  • Insects, animals, soil
3. Portal of Exit How germs leave the body
  • Respiratory tract
  • Intestinal tract
  • Urinary/genitourinary tract
  • Open wounds
  • Blood and body fluids
4. Transmission How germs are spread
* Refer to next page for a detailed explanation of how infections spread.
  • Direct physical contact
  • Respiratory droplet
  • Stool (fecal-oral route)
  • Contact with blood/body fluids
  • Indirect contact
  • Needle stick injury
  • Ingestion of contaminated food and water
  • Contaminated dust particles
  • Contaminated objects
  • Insects/animals
5. Portal of Entry How germs enter the body
  • Respiratory tract
  • Intestinal tract
  • Urinary/genitourinary tract
  • Open wounds
  • Mucus membrane, e.g. eye, mouth
6. Susceptible Host A person who gets an infection because he/she is unable to successfully fight the infection
  • Infants, elderly and debilitated.
  • Persons who are ill.
  • Children who are not fully immunized or have underdeveloped immune systems.
  • Persons taking certain drugs that lower their defenses against germs.
  • Persons with underlying disease conditions that lower their defense against other germs.


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