Seroprevalence of chikungunya virus infection in India, 2017: a cross-sectional population-based serosurvey

Since its re-emergence in 2005, chikungunya virus (CHIKV) transmission has been documented in most Indian states. Information is scarce regarding the seroprevalence of CHIKV in India. We aimed to estimate the age-specific seroprevalence, force of infection (FOI), and proportion of the population susceptible to CHIKV infection. We did a nationally representative, cross-sectional serosurvey, in which we randomly selected individuals in three age groups (5–8, 9–17, and 18–45 years), covering 240 clusters from 60 selected districts of 15 Indian states spread across all five geographical regions of India (north, northeast, east, south, and west). Age was the only inclusion criterion. We tested serum samples for IgG antibodies against CHIKV. We estimated the weighted age-group-specific seroprevalence of CHIKV infection for each region using the design weight (ie, the inverse of the overall probability of selection of state, district, village or ward, census enumeration block, and individual), adjusting for non-response. We constructed catalytic models to estimate the FOI and the proportion of the population susceptible to CHIKV in each region. From June 19, 2017, to April 12, 2018, we enumerated 117 675 individuals, of whom 77 640 were in the age group of 5–45 years. Of 17 930 randomly selected individuals, 12 300 individuals participated and their samples were used for estimation of CHIKV seroprevalence. The overall prevalence of IgG antibodies against CHIKV in the study population was 18·1% (95% CI 14·2–22·6). The overall seroprevalence was 9·2% (5·4–15·1) among individuals aged 5–8 years, 14·0% (8·8–21·4) among individuals aged 9–17 years, and 21·6% (15·9–28·5) among individuals aged 18–45 years. The seroprevalence was lowest in the northeast region (0·3% [95% CI 0·1–0·8]) and highest in the southern region (43·1% [34·3–52·3]). There was a significant difference in seroprevalence between rural (11·5% [8·8–15·0]) and urban (40·2% [31·7–49·3]) areas (p