Clinical Attack Rate of Chikungunya in a Cohort of Nicaraguan Children.

Chikungunya virus (CHIKV) was recently introduced into the Americas. In Nicaragua, the first endogenous transmission of CHIKV was recognized in September 2014. We used an ongoing dengue cohort study of children aged 2-14 years in Managua, Nicaragua, to document the attack rate of symptomatic chikungunya in a presumably naive population. From September 2014 through March 2015, the overall clinical attack rate of laboratory-confirmed CHIKV infection was 2.9% (95% confidence interval [CI]: 2.3%, 3.4%). The attack rate was greater in children ≥ 8 years of age (4.1%; 95% CI: 3.2%, 5.1%) than in those < 8 years of age (1.5%; 95% CI: 0.9%, 2.1%). The mean age of CHIKV cases presenting with typical chikungunya symptoms was 9.8 years, compared with 7.8 years for cases presenting with undifferentiated fever (P = 0.04). Our data suggest that the clinical attack rate in children may underestimate the true burden of disease as some children, especially young children, may experience more atypical symptoms (e.g., undifferentiated fever).