Segmentation of epidemic curves can sometimes be used to unmask a risk factor specific to a particular period of the epidemic. The following illustrate situations during which segmentation of epidemic curves could have been done to identify a specific vehicle.

The figure below shows that during an epidemic of Norwalk like virus in Sweden in 2002 a particular cluster occurred between February 26 and 28. An analysis restricted to that period may have identified specific risk factors that could otherwise go undetected if all cases were included in an analysis.


(Separate analysis of early and late cases in an outbreak can also be considered a form of segmentation