the measure of disease incidence observed in a small population sample over a short time — during an epidemic, for example.

The cumulative incidence of infection in a group observed over a period during an epidemic. This "rate" can be determined empirically by identifying clinical cases and/or by means of seroepidemiology. Because its time dimension is uncertain or arbitrarily decided, it should probably not be described as a rate. See also infection rate; secondary attack rate; seroepidemiology.

an incidence rate usually expressed as a percentage