7.2.1: The Chain of Infection
Recall in Chapter 6 how the epidemiologic triangle describes infectious diseases. Another model we can use to describe communicable disease spread is the chain of infection. See Fig. \(\PageIndex{1}\) below.
The chain of infection model describes each step in the transmission process, as well as those components of the epidemiological triangle (agent, host, environment). In order for a pathogen (agent) to be passed from one living organism to another, there must be a port of exit on the infected individual, a mode of transport, and a port of entry in a new susceptible individual. Hospitable environments are those that encourage this transmission, and potentially the growth of the pathogen outside of a host. Hygiene and workplace safety measures tend to focus on blocking routes of transmission and creating an inhospitable environment for pathogens (National Institute for Occupational Safety and Health, 2023).