Dengue serologic survey in Ribeirão Preto, São Paulo, Brazil

The city of Ribeirão Preto suffered a dengue 1 epidemic that began in November 1990 and ended in March 1991. A serologic survey designed to detect IgG antibodies to the four dengue serotypes and other flaviviruses was carried out in Ribeirão Preto during September and October of 1992. Dengue 1 antibodies were detected in 5.4% of the survey participants. Significantly higher seropositivity (9.3%) was found among subjects residing in the Northwest Sector of Ribeirão Preto than among those living in the city's other three sectors. The Northwest Sector also exhibited relatively high levels of breeding sites used by the Aedes aegypti vector, the highest number of reported dengue cases of any sector, and relatively poor socioeconomic conditions. The fact that the epidemic was limited mainly to the Northwest Sector probably resulted mainly from intense vector control and educational measures undertaken in response to the outbreak. As of the 1992 survey, most of the city's population remained vulnerable to dengue 1 infection; however, an estimated 23,000 with dengue 1 antibodies appeared to be at relatively high risk of developing dengue hemorrhagic fever/dengue shock syndrome in the event of infection with dengue 2. Both of these considerations indicate an ongoing need to maintain dengue education and vector control measures.