who were exposed to the suspectedrisk factor with the cumulative incidenceof those who were not exposed.Investigators’ conclusions based on the weight of the accumulated evidence are then written up in a report. Control measures need to be applied as soon as possible after an outbreak begins to minimize the number of
victims. An outbreak investigation may be initiated by an analytic study. In the Iowa trichinosis example, a case-control study enabled the investigators to ascertain which of three social events
was the source of the contaminated pork whose consumption triggered the outbreak.