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Serologic evidence of H7N9 common among poultry workers in China
Data from a serological survey of poultry market workers suggest that although none of the participants had a virologically confirmed influenza A(H7N9) infection, a high proportion had serologic evidence of infection between May and December 2013, according to researchers from the Shenzhen Center for Disease Control and Prevention in China.
“While the identification of mild H7N9 infections through sentinel surveillance indicates that the number of H7N9 infections substantially exceeds the number of laboratory-confirmed cases, our results are consistent with a substantial number of H7N9 infections among poultry workers despite relatively few confirmed cases having occurred in these persons,” the researchers wrote in Clinical Infectious Diseases.
The researchers conducted serological surveys of poultry market workers in May and December 2013. In May, poultry workers were recruited from 10 districts in Shenzhen, and in December, workers were recruited from seven districts where environmental swabs of poultry markets had been positive for H7N9. The participants provided blood samples and completed questionnaires.
In the May survey, the researchers obtained 501 serum specimens from workers, and in December, they obtained 375 specimens. In the May survey, 109 (21.8%) individuals had H7N9 antibody titers of 1:80 or more by hemagglutination-inhibition (HI) assay and 36 (7.2%) individuals had antibody titers of 1:160 or more. In the December survey, 211 (56.3%) individuals had H7N9 antibody titers of 1:80 or more and 56 (14.9%) had antibody titers of 1:160 or more.
Among the 96 workers who participated in both surveys, there was at least a fourfold increase in antibody titers from May to December. In a multivariable analysis, the risk of seroconversion was highest among female poultry workers (OR=2.71; 95% CI, 1.098-6.705) and among workers with an occupational exposure history of 10 or more years (OR=3.59; 95% CI, 1.246-10.354).
“Increases in the incidence of human cases in Shenzhen in January and February 2014 suggest that prevalence in poultry may have also increased during this period, compared to the preceding months, and further serological studies in poultry workers and the general population would be valuable to improve our understanding of the number of infections that have occurred in the present winter break,” the researchers wrote.
Disclosure: One researcher receives research funding from MedImmune and Sanofi Pasteur and consults for Crucell NV.