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Mayorga Perez, Orlando; Brinkhof, Martin W. G.; Egger, Matthias; Frösner, Gert; Herzog, Christian; Zwahlen, Marcel (2014): Decreasing Risk of Hepatitis A Infection in Leon, Nicaragua: Evidence from Cross-Sectional and Longitudinal Seroepidemiology Studies.
In: PLOS ONE 9(2), e87643
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Abstract

Nicaragua is highly endemic for hepatitis A. We aimed to provide an estimate of the change in the age-specific risk of hepatitis A virus (HAV) infection based on serological data from cross-sectional and longitudinal samples collected in Leon, Nicaragua, in 1995/96 (n = 979) and 2003 (n = 494). Methods: The observed age-specific prevalence of anti-HAV antibodies was correlated to the age-specific risk of infection by calculating the probability of freedom from infection at a specific age. Results: The proportion of seropositive children aged 1.5 to 6 years was 42% in 2003 compared to 67% in 1995/96. Estimated annual risk of infection for a 3-year old child was 30% (95% CI: 27.0%,33.1%) in 1995 and 15.5% (95% CI: 12.4%,19.0%) in 2003. There was good agreement between estimates based on cross-sectional and longitudinal data. The age-specific geometric mean of the quantified anti-HAV antibody levels assessed in 2003 was highest at age 4 and decreased steadily up to age 40. Conclusions: The substantially lower risk of HAV infection in 2003 than in 1995 for young children indicates a beginning transition from high to intermediate endemicity in Leon, Nicaragua. Consecutive age-stratified serosurveys are useful to assess changes in risk of infection following public health interventions. The decreasing age-specific GMC of anti-HAV antibodies during adulthood in a country with endemic HAV indirectly suggests that ongoing HAV exposure in the community has marginal boosting effect on antibody levels once protective immunity has been established by natural infection.