Here a contact refers to an association between a susceptible host and a reservoir of infection, which creates an opportunity for the infectious agents to enter the host.

In the stage of exposure, the susceptible host has come into close contact with the infectious agent, but it has not yet entered the host's body cells. Examples of an exposed host include:

a person who shakes hands with someone suffering from a common cold
a child living in the same room as an adult with tuberculosis
a person eating contaminated food or drinking contaminated water.