Report of dengue outbreak investigation in Jothinagar village, Thiruvallur district, Tamil Nadu, India, 2017: epidemiological, entomological, and geospatial investigations

Background: During July 2017 to August 2017, five cases of laboratory-confirmed dengue cases were reported from Jothinagar village, Tamil Nadu, India. The episode was investigated to confirm the existence of an outbreak and formulate appropriate recommendations for containment.Methods: The monthly occurrence of dengue cases from 2014 to 2017 was compared to confirm the outbreak. Additional blood specimens from 22 patients were sent for laboratory confirmation. We conducted active case search, eco-entomological survey, and geo-mapping of cases and Aedes breeding spots.Results: The occurrence of 36 cases of dengue in the village, previously free from the disease for the past 3.5 years, confirmed the outbreak. Twelve were laboratory-confirmed while the remaining 24 were probable cases. The attack rate was highest amongst females in the age group 11-15 years (10.8/100 population). Case fatality was zero. The house index, Breteau index, container index (CI) and pupal index was 37.7% (23/61), 54.1% (33/61), 16.7% (33/198) and 32.8% (20/61) respectively. Discarded tyres were the key productive containers (CI=28.36%). Geo-analysis suggested clustering of cases within 70 m of the Aedes breeding spots particularly within the central part of the village.Conclusions: Based on high entomological indices, an intensive vector elimination campaign was implemented with a special focus on managing discarded tyres. Geo-analysis can be incorporated in surveillance to identify clusters early for control measures.