Concurrent evaluation of epidemic St. Louis encephalitis: are you on the upward or downward side of the curve?

Laboratory confirmation of reported cases of St. Louis encephalitis (SLE) lags 2-4 weeks behind onset of illness. A review of our experience in Mississippi in 1975 and 1976 suggests that plotting the number of reported suspects greater than or equal to 50 years of age by date of onset and adjusting for reporting delays can help determine when the peak of the epidemic has passed. This method circumvents the obligatory delay of serologic tests, minimizes the bias of publicity and intensive surveillance, and may avoid promoting control procedure which are expensive, dangerous, and of uncertain efficacy.