Epidemiology and control of St. Louis Encephalitis in Birmingham, Alabama, 1975

Abstract

In 1974, 56 (78 per cent) of the United States cases of St. Louis encephalitis (SLE) occurred in Alabama, Mississippi, and Tennessee. As a result, the Jefferson County (Alabama) Health Department Implemented a comprehensive SLE surveillance program the following year. Jefferson County is located in northcentral Alabama and contains 34 incorporated municipalities, including Birmingham, the state's largest city. Thirty-two confirmed and four presumptive cases of SLE were identified in Jefferson County during 1975. Of these, 28 confirmed and two presumptive cases were Birmingham residents while the other four confirmed cases lived less than two kilometers from the city limits. The majority of the cases (25 confirmed, three presumptive) had clinical onsets between August 23 and September 27; the peak of the outbreak occurred during the week of August 31 when ten confirmed cases became ill. A total of 178 suspect cases were ultimately investigated. Of the 109 cases clinically diagnosed as aseptic meningitis, only eight (7.3 per cent) were subsequently confirmed as SLE. In contrast, 20 (44.4 per cent) of the 45 cases diagnosed as encephalitis were serologically confirmed. Sixteen of the 20 encephalitic cases were at least 55 years of age, while only two of those initially diagnosed as aseptic meningitis were in this age group.