Reference:
- Lecturer
The chain of infection is a model used in communicable disease to outline the process by which an infective agent (the first link in the chain) reaches a susceptible host (the last link in the chain). This is an important tool to combat communicable diseases. The following are the six links in the chain of infection, and how each one may be broken.
- Agent: the microorganism capable of producing disease.
- This is broken using disinfection (removing microorganisms) and sterilization (removing microorganisms and spores). This can be achieved through physical and chemical methods.
- The most common method for sterilization in hospitals is autoclaving, the application of heat and pressure at 15 PPI, 121°C/250°F.
- In lower-level facilities, sterilization is done with chemical soaking.
- At home, sterilization can be done with boiling.
- This is broken using disinfection (removing microorganisms) and sterilization (removing microorganisms and spores). This can be achieved through physical and chemical methods.
- Reservoir: the location where the microorganism remains. This may be other organisms (humans, animals, insects) or contaminated food, soil, and water.
- Human reservoirs: measles, mumps, HIV, STDs. People who carry the disease, yet does not show outward signs of infection are called carriers.
- Animal reservoirs: anthrax (sheep), rabies (dogs)
- Environment reservoirs: histoplasmosis (soil), toxoplasmosis (cat feces)
- Portal of Exit: a method by which microorganisms exit the reservoir. In humans, this can be through secretions (except tear and sweat; these are antimicrobial— they are part of the chemical barriers of the immune system), bodily fluids, sexual contact, etc.
- Mode of Transmission: the medium that the microorganisms travel by. This is generally divided between contact (most common), droplet (travels ~1 meter), airborne (travels >1 meter), and the fecal-oral route (ingestion of contaminated items).
- The weakest link of the chain of infection as it is easily broken. The most effective method of preventing infection is handwashing.
- Portal of Entry: a method by which microorganisms can enter a new host. This can be through breaks in the skin, the eyes, or other openings in the mucosa.
- Susceptible Host: a host adequately susceptible to the microorganism entering. This may be anyone, but is more likely for children (<5 years old, prior to immune system maturity), older adults, unimmunized people, and the immunocompromised.