• Nijuan Xiang, Tian Bai, Kai Kang, Hui Yuan, Suizan Zhou, Ruiqi Ren, Xiuying Li, Jiabing Wu, Liquan Deng, Ge Zeng, Xianjun Wang, Shenghua Mao, Jian Shi, Rongbao Gao, Tao Chen, Sumei Zou, Dan Li, Fiona Havers, Marc-Alain Widdowson, Carolyn M Greene, Yanping Zhang, Daxin Ni, Xiaoqing Liu, Qun Li, and Yuelong Shu.
• Chinese Center for Disease Control and Prevention, Beijing, China.
• Influenza Other Respi Viruses. 2017 Mar 1; 11 (2): 170-176.

BackgroundThe first human infections of novel avian influenza A(H7N9) virus were identified in China in March 2013. Sentinel surveillance systems and contact tracing may not identify mild and asymptomatic human infections of influenza A(H7N9) virus.ObjectivesWe assessed the seroprevalence of antibodies to influenza A(H7N9) virus in three populations during the early stages of the epidemic.Patients/MethodsFrom March 2013 to May 2014, we collected sera from the general population, poultry workers, and contacts of confirmed infections in nine Chinese provinces reporting human A(H7N9) infections and, for contacts, second sera 2-3 weeks later. We screened for A(H7N9) antibodies by advanced hemagglutination inhibition (HI) assay and tested sera with HI titers ≥20 by modified microneutralization (MN) assay. MN titers ≥20 or fourfold increases in paired sera were considered seropositive.ResultsAmong general population sera (n=1480), none were seropositive. Among poultry worker sera (n=1866), 28 had HI titers ≥20; two (0.11%, 95% CI: 0.02-0.44) were positive by MN. Among 61 healthcare and 117 non-healthcare contacts' sera, five had HI titers ≥20, and all were negative by MN. There was no seroconversion among 131 paired sera.ConclusionsThere was no evidence of widespread transmission of influenza A(H7N9) virus during March 2013 to May 2014, although A(H7N9) may have caused rare, previously unrecognized infections among poultry workers. Although the findings suggest that there were few undetected cases of influenza A(H7N9) early in the epidemic, it is important to continue monitoring transmission as virus and epidemic evolve.© 2016 The Authors. Influenza and Other Respiratory Viruses Published by John Wiley & Sons Ltd.

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