Pandemic Influenza A/H1N1 2009 Antibodies in the Metropolitan Area of Buenos Aires in Argentina.

Objective: To estimate the infection prevalence in Buenos Aires during the outbreak of pandemic influenza A/H1N1 2009 virus (A(H1N1)pdm09).Methods: A(H1N1)pdm09-specific antibodies were measured by hemagglutination inhibition assay in human serum samples collected 6 months after the outbreak and before the introduction of the A(H1N1)pdm09 vaccine in Argentina. Baseline levels of cross-reactive antibodies to A(H1N1)pdm09 were determined by testing 162 serum samples collected before 2009.Results: The overall seroprevalence of A(H1N1)pdm09 in 150 children and 427 adults was 28.9% (95% confidence interval (CI) 25-33%), with a 58.0% prevalence in children <19 years of age and an 18.7% prevalence in adults >= 19 years of age (p < 0.001). The prevalence was 43.5% in children < 5 years old and 60.6% among children aged 5-18 years. The prevalence in adults declined with increasing age: 24.9% in 19-39-year-olds, 9.7% in 40-59-year-olds, and 8.1% in those >60 years old. The prevalence of specific A(H1N1)pdm09 antibodies was higher compared with the baseline in children (p = 0.014), adolescents (p < 0.001), and adults < 40 years old (p = 0.017). Seroprevalence in health care workers was not different from the rest of the population (13.6% vs. 19.3%, respectively; p = 0.421).Conclusions: The prevalence of specific A(H1N1)pdm09 antibodies was high at 28.9%. The highest prevalence was observed in children, adolescents, and young adults. (C) 2013 The Authors. Published by Elsevier Ltd on behalf of International Society for Infectious Diseases. All rights reserved.