Epidemiology of dengue and related entomological and environmental factors - Surat City, Gujarat, India 2011-2016

Abstract

Purpose: Surat city observed a rising trend in dengue from 2011 to 2016. Our objectives were to estimate the incidence of dengue in terms of time, place and person, analyze the entomological indices pertaining to Aedes aegypti breeding and climatic factors for dengue transmission in the city. Methods & Materials: We analyzed the surveillance data of vector-borne disease control (VBDC) department from 2011 to 2016. We calculated age, sex and location specific cumulative incidence of dengue. The data was plotted to understand the seasonal distribution of cases. Median House index (HI), Breteau index (BI) and container index (CI) were calculated. Temperature, humidity, rainfall and number of patients were correlated with vector density using spearman correlation coefficient (rs). Results: Overall 2446 (11%) of 22101 suspected cases were confirmed positive for dengue as per IgM or NS1 ELISA tests. Incidence increased from 1.5 (2011) to 17.5 (2016) per 100,000 population. Incidence was higher among males. Median age of dengue cases was 20 years (Inter quartile range: 14-28). Five (16%) of 32 VBDC units had incidence above the city average since 2012. Incidence was highest post monsoon. The median HI and BI was <1% and the median CI was < 0.4% throughout the study period. Vector density was significantly correlated with humidity (rs = 0.556), rainfall (rs = 0.644) and number of cases (rs = 0.708). Peak vector density followed peak number of rainy days. Conclusion: Higher incidence in young males and low house index indicates the probable transmission away from the house. The reasons for high incidence in 5 VBDC units require further micro level evaluation to find out the risk factors. Climate is conducive for vector breeding.