Seroepidemiological survey among schoolchildren during the 2000-2001 dengue outbreak of Ratchaburi Province, Thailand

From August 2000 to 2001, a dengue outbreak occurred in Mueang district, Ratchaburi Province, Thailand. About 800 cases of dengue infection were reported, and among them, 49.5% were clinically diagnosed as dengue hemorrhagic fever according to the WHO criteria. During the outbreak, the incidence rate of dengue infection in Hin Gong subdistrict was 2.9 per 1,000 population. A seroepidemiological survey was conducted among primary schoolchildren from July 2000 to June 2001, to monitor dengue transmission. In a baseline survey, 283 children were surveyed for dengue antibody and 71% were IgG seropositive. In June 2001, the rate of dengue infection showed an increase of 8.8% with 8.0% among immune children and 10.3% among naive schoolchildren. Among 283 schoolchildren, 90 were followed up 3 times, in September and December 2000, and June 2001. An increase in the rate of seroconversion was observed in the period September to December 2000, while the peak dengue outbreaks in the dry season occurred in February 2001. Serosurveys among schoolchildren appear to be early warning system, and can be advantageous in early dengue control actions, in order to break the chain of transmission before an impending epidemic.