Incidence

In epidemiology, incidence refers to new cases of disease or new occurrences of medical conditions such as becoming infected with a virus; it is contrasted with prevalence, which includes both new and existing cases or occurrences. While historically the term incidence was limited to disease or death, it is increasingly being used more broadly to quantify the occurrence of events, not just a new disease. Examples of incident cases or events include when a person develops diabetes, becomes infected with HIV, starts [Page 529]smoking, or is admitted to the hospital. In each of these situations, individuals go from an occurrencefree state to having the occurrence.

It is important for epidemiologists to make a clear distinction between incidence and prevalence. While incidence refers to a new disease ...