title: Decreasing risk of hepatitis A infection in León, Nicaragua: evidence from cross-sectional and longitudinal seroepidemiology studies.
abstract: OBJECTIVE
  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 León, 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 León, 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.
authors: Department of Microbiology and Parasitology, Faculty of Medical Sciences, National Autonomous University, León, Nicaragua.
authors: Orlando
authors: O
authors: Mayorga Perez
authors: Institute of Social & Preventive Medicine (ISPM), University of Berne, Berne, Switzerland.
authors: Martin W G
authors: MW
authors: Brinkhof
authors: Institute of Social & Preventive Medicine (ISPM), University of Berne, Berne, Switzerland.
authors: Matthias
authors: M
authors: Egger
authors: Max von Pettenkofer Institute, Ludwig-Maximilians University, Munich, Germany.
authors: Gert
authors: G
authors: Frösner
authors: Crucell Switzerland AG, Berne, Switzerland.
authors: Christian
authors: C
authors: Herzog
authors: Institute of Social & Preventive Medicine (ISPM), University of Berne, Berne, Switzerland.
authors: Marcel
authors: M
authors: Zwahlen
mesh_terms: D000293:Adolescent; D000328:Adult; D002648:Child; D002675:Child, Preschool; D003140:Communicable Disease Control; D003430:Cross-Sectional Studies; D062665:Epidemiological Monitoring; D005260:Female; D006506:Hepatitis A / Q000097:blood* / Q000175:diagnosis* / Q000453:epidemiology*; D030041:Hepatitis A virus; D006801:Humans; D007223:Infant; D008137:Longitudinal Studies; D008297:Male; D009527:Nicaragua; D015995:Prevalence; D012306:Risk; D055815:Young Adult