The Incubation and Infectious Period

Understanding how a disease is transmitted is only part of the story. You must also know when the disease was transmitted. The incubation period, which is the time between the exposure to an infectious agent and the onset of symptoms. For a chronic disease, this is referred to as the latency period. The infectious period is the time when an infected person can transmit a pathogen.

The periods of time before the onset of symptoms are very important in the dynamics of disease spread because they dictate when cases will be detected relative to the time of infection and the incubation period. In some instances, transmission can occur before clinically specific symptoms appear. This is called the prodromal period. Prodromes or prodromal symptoms are early AND non-specific for diagnosis. The infectious period can occur as soon as one to two days after infection.

To help illustrate the prodromal period, let us look at an example: a patient coming down with a case of chicken pox. During the incubation period, the patient often develops prodromal symptoms of a fever or a runny nose before the actual blisters erupt. The disease is in the body and shows early signs and symptoms before symptoms specific to the disease arise.