ABSTRACT
Introduction: In October 2009; the first outbreak of pandemic influenza A(H1N1) 2009 virus in Madagascar occurred at a school in Antananarivo. Among the first 12 cases; five were reported in boarding pupils at the school. The school closed 10 days into the outbreak. Mass oseltamivir prophylactic treatment was used to contain the outbreak. This study aimed to determine the transmission of infection among boarding school pupils and to evaluate the adverse effects of oseltamivir chemoprophylactic treatment and their impact on compliance.Methodology: After conducting an initial investigation of the outbreak we administered a questionnaire to 132 boarders who were present after the school re-opened. Questions addressed symptoms of influenza-like illness; compliance with chemoprophylaxis; and adverse effects. Results: Of 59 boarders; 20 (45.0) had confirmed pandemic influenza A (H1N1) infection. Among the asymptomatic boarders; compliance with oseltamivir chemoprophylaxis was moderate: 56.2took the full 10-day course; and 66.9completed at least seven days. In contrast; among symptomatic boarders; only two did not take the full course of oseltamivir. Fifty percent of the boarders receiving oseltamivir experienced symptoms such as fatigue (38.7); difficulty concentrating (22.6) and headaches (19.4). Bad compliance was not associated with adverse effects.Conclusion: Since the symptoms of pandemic influenza A(H1N1) 2009 virus were generally mild; the burden of adverse effects must be considered when deciding on mass oseltamivir chemoprophylaxis among teenagers