Outbreaks of dengue in Central India in 2016: Clinical, laboratory & epidemiological study

Background & objectives: Dengue virus (DENV) causes outbreaks and sporadic cases in tropical and subtropical countries. Documenting intricacies of DEN outbreaks is important for future interventions. The objective of this study was to report clinical, laboratory and epidemiological features of DEN outbreaks reported in different districts of Central India in 2016. Methods: In 2016, outbreaks (n=4) suspected of DEN were investigated by rapid response team. Door-to-door fever and entomological surveys were conducted. Blood samples were collected and tested using NS1 or IgM ELISA; real-time reverse transcription-polymerase chain reaction was done to identify serotypes of DEN virus (DENV). NS1-positive samples were tested for the presence of IgG by ELISA. Clinical and demographic data were collected and analyzed. Results: Outbreaks occurred in both urban and rural areas in monsoon season and Aedes aegypti was identified as the vector. Fever, chills, headache and myalgia were the major symptoms; no fatality was recorded. Of the 268 DEN suspects, 135 (50.4%) were found serologically positive. DEN positivity was higher (n=75; 55.56%) among males and in the age group of 16-45 yr (n=78; 57.8%). DENV 3 followed by DENV 2 were detected as the major responsible serotypes. High attack rates (up to 38/1000) and low cumulative IgG prevalence (14.9%) were recorded in rural areas. Interpretation & conclusions: Our study showed that DENV 3 was the major serotype responsible for outbreaks that occurred in monsoon. High attack rates and lower number of secondary infections in rural areas indicated that DENV is emerging in rural parts of Central India. Early diagnosis at local level and timely intervention by mosquito control activities are needed to avoid such outbreaks in future.