Rapid assessment of vectorborne diseases during the Midwest flood--United States, 1993.

Heavy spring and summer rainfall during 1993 caused the most extensive flash and riverine flooding ever recorded in the upper midwestern United States. In portions of the flood region,* standing water provided large expanses of habitat capable of producing large populations of the mosquitoes Culex pipiens and Cx. tarsalis. These species can rapidly amplify transmission of the arboviruses that cause St. Louis encephalitis (SLE) and western equine encephalitis (WEE). Although information from state health departments in the disaster area indicated minimal SLE or WEE activity in the region before the flooding, large vector populations in certain areas following the flooding increased the potential for exposure of residents and emergency workers to arboviral infection. To determine the risk for arboviral disease in the disaster area, CDC, in collaboration with state and local health departments, conducted surveillance during August-September 1993. This report summarizes the results of the surveillance activity.