The Chain of Infection Model

This model explains the spread of a communicable disease from one host (or person) to another. The basic idea represented in the chain of infection is that individuals can break the chain (reduce the risk) at any point; thus the spread of the disease can be stopped.

 Chain of infection.

Component of the model


Preventive measures

Communicable disease Disease caused by an infectious agent Pasteurization, chlorination, antibiotics, disinfectants, hand washing, etc.
Human reservoir The human being who is harboring the infectious agent Isolation, surveillance, treatment with medications, etc.
Portal of exit The body part through which the infectious agent is exiting from the reservoir, for example the mouth or the anus Utilization of handkerchiefs, condoms, hair nets, insect repellents, hand washing, etc.
Transmission The spread of the infectious agent from the reservoir to the host Isolation, hand washing, mosquito control, sexual abstinence, condom users, etc.
Portal of entry The body part through which the infectious agent will enter the new host, for example the skin after a mosquito bite, the mouth Condoms, hair nets, insect repellents, hand washing, etc.
Establishment of disease in new host (susceptible person)

The host develops signs and symptoms of the new disease.

Immunizations, health education, nutrition promotion; sexual abstinence, condom use, etc.

There are two sets of components that have some similar preventive measures. As a way of helping yourself become familiar with this chart see if you can spot which these are.
The portal of entry and exit both involve preventive measures such as hand washing, condoms, hair nets and insect repellents, while the human reservoir and transmission measures both involve isolation. Be sure you have a clear picture of the definition and prevention of each element before you continue.
With the application of such information, health education can help to create programs that are aimed at breaking the chain and reducing the risks of infection in other people.

The communicable disease model

  • The communicable disease model presents three elements; infectious agent, host and environment, as the minimal requirements for the presence and spread of a communicable disease in a population.
  • The infectious agent is the element that must be present for the disease to occur and spread. Bacteria, viruses and parasites are examples of infectious agents.
  • The host is any susceptible organism. Plants, animals or humans can be invaded by the infectious agent and become the host.
  • The environment includes all other factors that either promote or prohibit disease transmission.