8.2 Epidemics, Outbreaks, and Clusters

An epidemic happens when there are more cases of a disease than expected: cases involving a wide geographic area, a specific group of people, and over a specific period of time. All cases in an epidemic have some common cause or at the very least, are related in some way.

An outbreak is an epidemic, albeit localized to one area.

A cluster refers to a group of cases that occur during a specific place and over a specific period of time. It does not matter if the number of cases in a cluster is more than expected.