8. Outbreak epidemiology

An outbreak occurs when the number of new cases of a disease observed in a particular situation and a particular geographical area over a relatively short period is larger than would be expected based on the descriptive epidemiology of that disease (chap.​ 1). An increase in the incidence of a disease in a large population and/or area is referred to as an epidemic. We therefore need to have a good idea of the number of cases that can be expected in a particular period, place and population, and what variability is normal. Proper surveillance is very important, then, if we want to be able to recognize and investigate true outbreaks.