Background The primary objective of this study was to find the performance of the 2009 probable case definition of dengue and compare it with the definition given by the WHO-SEAR expert group in 2011. Methods A cross-sectional study was conducted in Thiruvananthapuram district of Kerala, which is hyperendemic for dengue. A consecutive series of 851 participants defined by the selection criteria were recruited from the primary, secondary, and tertiary health care settings. Sensitivity, specificity, predictive values, and likelihood ratios of the clinical case definitions were calculated using reverse transcriptasepolymerized chain reaction (RT-PCR) as gold standard in case of fever less than or equal to 5 days and serology (IgM positivity) for fever .5 days. Diagnostic odds ratio (DOR) was also calculated as a single indicator of performance of the case definition. Results The 2009 World Health Organization (WHO) case definition had a sensitivity of 76.4% (69.6-82.1) and negative predictive value of 87.5%. The 2011 WHO-SEAR expert group case definition had a higher sensitivity of 87.9% (82.2-91.9) but lower negative predictive value of 86.6%. The three independent criteria which were significantly associated with dengue were thrombocytopenia less than 150 000 (OR 2.80), leukopenia (OR 2.28), and absence of backache (OR 2.68). The performance of 2009 case definition was better (DOR 2.4) than the 2011 WHO-SEAR expert group case definition. This was further enhanced when thrombocytopenia was specified as platelet count less than 150 000 (DOR2.7). When 'no backahe' was added as an additional criteria, the performance of both definitions improved. Conclusions The 2009 WHO case definition has better discriminatory power than the 2011 WHO-SEAR expert group case definition. The performance of 2009 WHO case definition is enhanced by specifying thrombocytopenia as platelet count less than 150 000. The inclusion of 'no backache' further improves the discriminatory power. This may be more useful in primary care settings, to rule out dengue.

Background: The state of Kerala is endemic for Dengue. The district Kollam in Kerala reported increasing fever trend as per the state surveillance report. So an investigation was planned to estimate the burden of fever in the locality of reported Dengue cases, to calculate vector indices around areas of confirmed cases and to study the clinical profile and risk factors of Dengue fever.Methods: A Cross sectional survey with entomological survey was conducted in houses around the confirmed dengue cases. A case control analysis was done with Dengue positive as cases and negative test results among the fever cases as controls .Odds ratio was calculated for strength of association and statistical test of significance using Chi Square test.Results: Total number of households visited was 80, numbers of hospitalized patients were 26.Total fever cases studied were 46 of which 30.4% and 8.7% were positive for IgM and IgG Dengue respectively.PCR was positive in 28.3%. Chills [OR – 3.55 (1.05-12.1)], p value < 0.03, was found to be significantly associated with Dengue positivity .Dengue positivity was higher among housewives, but not found to be statistically significant. 51.2% of the households had water storage containers at home. Breteau index in one of the areas surveyed was 60 and 52.Conclusion: More awareness needed to be generated among the public of the importance of identifying and destroying the vector breeding sites around households as very often breeding sites are found right inside houses.