Title: The chain of infection model
Course: Health Education, Advocacy and Community Mobilisation Part 1 - Ethiopia (Full)

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. Figure 3.4 shows the basic links in the chain and Table 3.1 explains the links in detail.

Figure 3.4 Chain of infection model.

Table 3.1 Chain of infection.

Component of the model | Definition | Preventive measures
Communicable disease | Disease caused by an infectious agent | Pasteurization, chlorination, antibiotics, disinfectants, hand washing, etc.
Human reservoir | The human being who is harbouring 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 | Utilisation of handkerchiefs, condoms, hair nets, insect repellents, hand washing and latrines, 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.

Now look at Table 3.1 carefully again. 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.

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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 programmes that are aimed at breaking the chain and reducing the risks of infection in other people. As a Health Extension Practitioner, you will be able educate individuals and your community about these interventions and help to implement many of them.