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Influenza A (H1N1) infections among healthcare workers: a cause for cautious optimism
  1. Judy Sng,
  2. David Koh,
  3. Gerald Koh
  1. Department of Epidemiology and Public Health, Yong Loo Lin School of Medicine, National University of Singapore, Singapore
  1. Correspondence to David Koh, Block MD3, 16 Medical Drive, Singapore 117597; ephkohd{at}

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The 2009 swine flu (influenza A H1N1) pandemic defied predictions that the next influenza outbreak was likely to be due to avian influenza arising from H5N1-endemic countries in Southeast Asia. As the world struggled to cope with the global financial meltdown, a new unexpected influenza challenge emerged from the Americas, but with the public health community better prepared than before. Although the avian influenza predictions have not occurred yet, the dire warnings were not misplaced, as the pandemic planning that ensued greatly helped decision makers and healthcare professionals around the planet to deal with the current A(H1N1) outbreak.

The numbers of A(H1N1) infections have increased rapidly. On 11 June 2009, after nearly 30 000 laboratory confirmed cases reported in 74 countries, the WHO declared the A(H1N1) outbreak the first pandemic of this century.1 Estimates of the reproduction number (defined as the “number of cases that one case generates on average over the course of their infectious period”) for A(H1N1) range from 1.4 to 1.6, which are higher than for the usual strains of seasonal influenza. However, compared to the 10% mortality rate seen with SARS, the case fatality ratio for A(H1N1) is lower and estimated to be from 0.2% to 0.4%.2 3

Although no official numbers have …

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