Chain of infection

Last revised by Joshua Yap on 2 Oct 2022

The chain of infection, also known as the chain of transmission, refers to the chronological sequence in which an infectious agent, and hence disease, is able to disseminate through a population. The chain results from a complex interaction between the agent, environment, and host.

Typically the chain comprises these key components:

  1. reservoir

  2. portal of exit

  3. mode of transmission

  4. portal of entry

  5. host

At the start of the chain, the infectious entity (e.g. virus) lies and replicates in a natural reservoir; this may be an organism or somewhere in the environment (e.g. a lake or the soil). By some means, the infective agent leaves its reservoir via a portal of exit, and employing a mode of transmission, passes through a portal of entry to reach its host 1.

Clinical significance

A good understanding of the chain of infection is of key importance in controlling and ultimately preventing any infectious disease. If one of the links of the chain can be broken, the transmission can be halted and the disease stopped 1.

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