Dengue and Chikungunya Seroprevalence in an Urban Low-Income Cohort in Delhi: A Cross-Sectional and Nested Longitudinal Study

Objectives: The aim of this study was to ascertain the seroprevalence and determinants of dengue virus (DENV) and chikungunya virus (CHIKV) seropositivity in Delhi, India. Methods: This cross-sectional serosurvey with a nested longitudinal immunological sub-study was conducted in an urban resettlement and slum settlement in the North-East district of Delhi in individuals aged ≥2 years. Dengue and Chikungunya virus IgG antibodies were screened using indirect enzyme-linked immunosorbent assay (ELISA), and a longitudinal subset of 100 paired IgG-seropositive samples was further characterized via a plaque reduction neutralization test (µPRNT50) to evaluate changes in functional neutralization over time. Results: A total of 752 participants, including 56.65% female participants, were included in the study. Of the participants studied, 81.91% (95% CI: 78.97, 84.60; n = 616) were positive for IgG antibodies against DENV, and 28.32% (95% CI: 25.13, 31.69; n = 213) were positive for CHIKV IgG antibodies. µPRNT50 confirmed stable, near-universal CHIKV neutralization (97% baseline, 98% endline). However, DENV neutralizing antibody showed a significant contraction for DENV-3 (79% baseline, 60% endline) and DENV-4 (69% baseline, 60% endline), while DENV-1 (76%) and DENV-2 (77% to 80%) antibodies remained stable. Individuals living in households with screened windows had significantly lower odds of contracting DENV infection (AOR: 0.36; 95% CI: 0.21, 0.61) and CHIKV infection (AOR: 0.63; 95% CI: 0.43, 0.90) compared with those living in households without screened windows. Further, individuals from households with uncovered containers with stagnant water had 50% higher odds of CHIKV infection than those without such containers (AOR: 1.55; 95% CI: 1.05, 2.29). Conclusions: This study revealed a high burden of DENV and CHIKV exposure in this high-risk urban population. While neutralization remained stable for CHIKV, DENV-1, and DENV-2, waning DENV-3 and DENV-4 antibodies suggest differential serotype-specific immunity in the participants.