Chain of Infection – Level 3 Health and Social Care Cambridge Technical Revision

Understanding the Chain of Infection

Chain of infection: A process that begins when an agent leaves its reservoir, or host, through a portal of exit, is conveyed by some mode of transmission, and enters through an appropriate portal of entry to infect a susceptible host.
Agent: This refers to the microorganism - bacteria, virus, or other pathogen - that causes the infection.
Reservoir: The habitat in which the infectious agent lives, grows and multiplies. Humans, animals, and the environment can all perform this function.
Portal of exit: This is the pathway by which the infectious agent leaves its host. This could be the respiratory tract (e.g. through coughing, sneezing), gastrointestinal tract (e.g. through faeces), or skin/mucous membranes (e.g. through cuts, wounds).

Direct contact transmission: This happens when microorganisms are transferred from an infected person to another person without a third person involved. It commonly involves contact with body surfaces, skin-to-skin contact, kissing, sexual intercourse, and airborne droplet spread.
Indirect contact transmission: This involves intermediate objects or materials (fomites) being contaminated with an infectious agent. For example, microorganisms can be present on towelettes, bedding, toys, injection needles, food, and water.
Airborne transmission: Some diseases are spread in small particles in the air, such as in dust or droplets generated with talking, coughing, or sneezing.
Vector-borne transmission: This is where vectors (like insects) telegraph pathogens from one host to another. Examples: Mosquitos transferring the malaria parasite, ticks transferring the Lyme disease bacteria.

Portal of entry: This is the means by which the pathogen enters a new host. The portal could be the respiratory tract, digestive system, or broken skin such as a cut or abrasion.
Susceptible host: For an infection to establish, the host - the person or animal - must be susceptible to that pathogen. Various factors can affect susceptibility, such as general health, age, or immune status.

Infection prevention relies on interrupting the chain of infection by targeting the links in the chain through techniques such as good hand hygiene, vaccination, safe disposal of waste, and maintaining clean environments.
Hand Hygiene: Regular and correct handwashing significantly reduces the risk of pathogen transmission.
Vaccination: This can help the host develop immunity and prevent certain infections.
Waste management and environmental cleanliness: Proper disposal of medical waste and maintaining a clean environment can eliminate the reservoirs of infection.
Education: Understanding the chain of infection can help individuals make informed decisions about how to prevent the spread of pathogens.

Standard precautions are practices used in healthcare to reduce the risk of transmission of pathogens from both recognised and unrecognised sources. They are applied to all patients, regardless of their diagnosis or presumed infectious status.
These precautions include ensuring good hygiene practice, using personal protective equipment (PPE) such as gloves and aprons when necessary, and managing clinical equipment and the environment adequately to minimize the risk of cross-contamination.