An article in the New England Journal of Medicine online edition, June 11, 2009, reported on the results of a serologic survey of poultry farmers, workers in broiler and pig processing plants and live bird markets in the Guangzho metropolitan area in Guangdong Province of Southern China.

Less than 1% of poultry retailers in food markets and wholesalers in live bird markets showed antibodies to H5. In contrast 16% of the retailers in markets and 7% of the wholesalers showed antibodies to H9 avian influenza as did 6% of workers in commercial farms. All three groups were regarded as significantly different on statistical analysis from the general population which served as a control.

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An antibody response against H5 influenza was not detected in subsistence poultry farmers, workers on commercial swine operations or employees of food markets not in contact with poultry. Although a small proportion of these groups showed from 1.8-2.8% reactor rates, these values were not significantly different from the general population which showed a 1.3% reactor rate against H9.

Editorial Comment: The result of the study is consistent with the knowledge that close contact with live poultry either through handling birds or processing in wet markets exposes workers to infection if flocks are excreting influenza virus at the time of delivery. The presence of circulating virus in markets represents a potential for recombinant events which could result in the emergence of strains of avian influenza with increased pathogenecity for humans. Failure to control avian influenza through applying biosecurity and vaccination contributes to endemic infection. H9 strain AI is presumed to be endemic in poultry flocks in the province. Maintaining a live bird marketing system perpetuates the danger of dissemination of virus from poultry farms to the general population.