Field- and laboratory-based active dengue surveillance in Chennai, Tamil Nadu, India: observations before and during the 2001 dengue epidemic.

BACKGROUND: Dengue cases are reported every year in the city of Chennai, Tamil Nadu, India. Since April 2001, longitudinal field- and laboratory-based active dengue surveillance has been carried out in Chennai to study dengue trends.

METHOD: A serologic survey of people in Chennai using the hemagglutination inhibition test (HIT) was performed to determine evidence of prior exposure to dengue virus infections. Dengue virus infections and their serotypes were demonstrated in vectors. The serum samples from clinical dengue patients were analyzed for dengue virus-specific immunoglobulins M (IgM) and G (IgG) antibodies by 2 commercial ELISA kits.

RESULTS: There was an increase in the percentage of children with monotypic antibody responses to dengue in the later survey (April 2.2%, September 9.93%). DEN-3 serotype infections were demonstrated in male Aedes aegypti mosquitoes collected in September 2001. Dengue virus infection was diagnosed in 74.5% (143/192) of cases. While dengue-specific IgM responses were predominant among infants with dengue fever, IgG and mixed responses (M + G) were seen in 85% of the children with severe forms of dengue.

CONCLUSION: The findings from these investigations suggest that antibody surveys in children and virus detection in vectors may be included as early warning system parameters in laboratory-based proactive dengue surveillance.