Studies on dengue and dengue haemorrhagic fever (DHF) in West Bengal State, India

A large outbreak of dengue and dengue haemorrhagic fever (DHF) occurred from August to November 2005 involving all districts of West Bengal. Altogether 6293 persons were serologically diagnosed to be suffering from dengue through detection of IgM antibodies, with 27 (0.42%) seropositive deaths. In Kolkata alone 3967 persons were affected with 14 deaths. A total of 874 sera samples from febrile patients were quantitatively analysed for IgG and IgM antibodies using the IVD microwell ELISA dengue fever test kit. In 21.6%, no antibody was detected and 52.6% had only IgG antibodies. In 8.9% only IgM antibodies and in 16.8% both IgG, IgM antibodies were present, suggesting primary and secondary dengue respectively. About 10% of secondary dengue would develop DHF. As in this outbreak secondary dengue was 65.3% of total dengue cases, so of the 6293 dengue victims presumably, 3998 had secondary dengue, thus having risk of DHF in about 400 persons. Case fatality rate amongst DHF patients was 8.5%. This study also indicated that DHF would be a nagging problem in coming days. Age-group analysis of primary and secondary dengue cases revealed that although secondary cases occurred in all ages, more of primary cases belonged to younger ages (1-10) years and more of secondary cases in middle to older ages. Prevailing type during this outbreak was DEN3. This epidemiological study of an outbreak categorized prevalence of primary and secondary dengue, calculated risk factors for precipitation of DHF, model of which could be utilized to compare and evaluate future epidemiological pattern, where-ever and whenever applicable.