Deciding an Outbreak is Over

An outbreak ends when the number of new illnesses reported drops back to the number normally expected. The epidemic curve helps investigators see that illnesses are declining. Even when illnesses from the outbreak appear to have stopped, public health officials still continue surveillance for a few weeks to be sure cases don’t start to increase again. If that happens, they continue or restart their investigation. It could be that the source was not completely controlled, or that a second contamination involving another food or location is linked to the first outbreak.