Epidemiological features of and public health response to a St. Louis encephalitis epidemic in Florida, 1990-1

A St. Louis encephalitis (SLE) epidemic in Florida during 25 weeks in 1990- 1, resulted in 222 laboratory-diagnosed cases, an attack rate in the 28 aff ected counties of 2.25/100000. Disease risk rose with advanced age, to 17.1 4/100000 in persons over 80 years, and all 14 fatal cases were in persons o ver 55 years (median, 70 years). Community serosurveys in Indian River Coun ty, the epicenter of the outbreak (attack rate 21/100000), showed acute asy mptomatic infections in 3.6% of the persons surveyed, with higher rates in persons with outdoor occupational exposure (7.4%) and in clients of a shelt er for the indigent (13.3%). A matched case-control study found that evenin g outdoor exposure for more than 2 h was associated with an increased risk for acquiring illness (odds ratio [OR] 4.33, 95% CI 1.23-15.21) while a num ber of recommended personal protective measures were protective. Four SLE p atients were dually infected with Highlands J virus, the first reported cas es of acute infection with this alphavirus. The case-control study provided the first evidence that a public education campaign to reduce exposure had a protective effect against acquiring the disease.