Background: To probe seroepidemiology of the 2009 pandemic influenza A (H1N1) among health care workers\r\n(HCWs) in a children�s hospital.\r\nMethods: From August 2009 to March 2010, serum samples were drawn from 150 HCWs in a children�s hospital in\r\nTaipei before the 2009 influenza A (H1N1) pandemic, before H1N1 vaccination, and after the pandemic. HCWs who\r\nhad come into direct contact with 2009 influenza A (H1N1) patients or their clinical respiratory samples during\r\ntheir daily work were designated as a high-risk group. Antibody levels were determined by hemagglutination\r\ninhibition (HAI) assay. A four-fold or greater increase in HAI titers between any successive paired sera was defined\r\nas seroconversion, and factors associated with seroconversion were analyzed.\r\nResults: Among the 150 HCWs, 18 (12.0%) showed either virological or serological evidence of 2009 pandemic\r\ninfluenza A (H1N1) infection. Of the 90 unvaccinated HCWs, baseline and post-pandemic seroprotective rates were\r\n5.6% and 20.0%. Seroconversion rates among unvaccinated HCWs were 14.4% (13/90), 22.5% (9/40), and 8.0% (4/\r\n50) for total, high-risk group, and low-risk group, respectively. Multivariate analysis revealed being in the high-risk\r\ngroup is an independent risk factor associated with seroconversion.\r\nConclusion: The infection rate of 2009 pandemic influenza A (H1N1) in HCWs was moderate and not higher than\r\nthat for the general population. The majority of unvaccinated HCWs remained susceptible. Direct contact of\r\ninfluenza patients and their respiratory samples increased the risk of infection
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