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

Abstract

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 affected counties of 2.25/100,000. Disease risk rose with advanced age, to 17.14/100,000 in persons over 80 years, and all 14 fatal cases were in persons over 55 years (median, 70 years). Community serosurveys in Indian River County, the epicenter of the outbreak (attack rate 21/100,000), showed acute asymptomatic infections in 3.6% of the persons surveyed, with higher rates in persons with outdoor occupational exposure (7.4%) and in clients of a shelter for the indigent (13.3%). A matched case-control study found that evening 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 number of recommended personal protective measures were protective. Four SLE patients were dually infected with Highlands J virus, the first reported cases 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.

Modifiable Risk Factors for West Nile Virus Infection during an Outbreak—Arizona, 2010

“…31,32 However, air-conditioner use and presence of door and window screens were common among both case-patients and control-subjects in our study and did not protect against WNV infection. A finding similar to ours was obtained during a WNV outbreak in New York in 1999.…”

“…mosquitoes, also have been associated with time spent outdoors and not wearing long sleeves and long pants. 30,31 One possible reason our study did not identify modifiable behavioral risk factors might be that few study participants actually adhered to recommended personal protective behaviors. For example, 80% of case-patients and control-subjects reported never using insect repellent.…”

The contribution of rodent models to the pathological assessment of flaviviral infections of the central nervous system

“…Outbreaks of encephalitis resulting from SLEV infection are typically associated with periods of rainfall followed by warm, dry intervals that favor virus amplification in poikilothermic mosquito vectors and provide optimal breeding conditions for Culex species mosquitoes [135,138]. Such outbreaks have been pronounced in close proximity to enzootic habitats, most notably in California [136], Florida [99], Texas [26] and Louisiana [64]. A constellation of ecological factors, including temperature and rainfall [33] in addition to bird and human seroprevalence rates, are undoubtedly associated with the potential for the initiation of outbreaks [137].…”

Evaluation of St. Louis encephalitis virus/dengue virus type 4 antigenic chimeric viruses in mice and rhesus monkeys

“…More than 10,000 cases of severe disease have been described since then in the United States of America, and the virus remains endemic throughout most of the country. The most recent extensive outbreak of disease associated with SLE was in 1990 when over 200 cases with 14 deaths were reported in central Florida [3]. SLE is also endemic in Central and South America, and recent reports have indicated increased human disease associated with SLE in Brazil and Argentina [4,5].…”