Vernon J. Lee, M.B., B.S., M.P.H., Jonathan Yap, M.B., B.S., Alex R. Cook, Ph.D., Mark I. Chen, M.B., B.S., Ph.D., Joshua K. Tay, M.B., B.S., Boon Huan Tan, Ph.D., Jin Phang Loh, M.Sc., Seok Wei Chew, B.Sc., Wee Hong Koh, B.Sc., Raymond Lin, M.B., B.S., Lin Cui, Ph.D., Charlie W.H. Lee, M.Sc., Wing-Kin Sung, Ph.D., Christopher W. Wong, Ph.D., Martin L. Hibberd, Ph.D., Wee Lee Kang, M.B., B.S., M.Med., Benjamin Seet, M.B., B.S., M.P.H., and Paul A. Tambyah, M.D. NEJM Volume 362:2166-2174 June 10, 2010 Number 23
Background From June 22 through June 25, 2009, four outbreaks of infection with the pandemic influenza A (H1N1) virus occurred in Singapore military camps. We report the efficacy of ring chemoprophylaxis (geographically targeted containment by means of prophylaxis) with oseltamivir to control outbreaks of 2009 H1N1 influenza in semiclosed environments.
Results A total of 1175 personnel were at risk across the four sites, with 1100 receiving oseltamivir prophylaxis. A total of 75 personnel (6.4%) were infected before the intervention, and 7 (0.6%) after the intervention. There was a significant reduction in the overall reproductive number (the number of new cases attributable to the index case), from 1.91 (95% credible interval, 1.50 to 2.36) before the intervention to 0.11 (95% credible interval, 0.05 to 0.20) after the intervention. Three of the four outbreaks showed a significant reduction in the rate of infection after the intervention. Molecular analysis revealed that all four outbreaks were derived from the New York lineage of the 2009 H1N1 virus and that cases within each outbreak were due to transmission rather than unrelated episodes of infection. Of the 816 personnel treated with oseltamivir who were surveyed, 63 (7.7%) reported mild, nonrespiratory side effects of the drug, with no severe adverse events.
Conclusions Oseltamivir ring chemoprophylaxis, together with prompt identification and isolation of infected personnel, was effective in reducing the impact of outbreaks of 2009 H1N1 influenza in semiclosed settings.
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