• Salah Uddin Khan, Benjamin D Anderson, Gary L Heil, Song Liang, and Gregory C Gray.
• Department of Environmental and Global Health, College of Public Health and Health Professions Emerging Pathogens Institute, University of Florida, Gainesville.
• J. Infect. Dis. 2015 Aug 15; 212 (4): 562-9.

IntroductionGiven that influenza A(H9N2) is recognized as a pandemic threat, we evaluated the overall burden of influenza A(H9N2) infections among avian-exposed human populations.MethodsWe performed a systematic search of PubMed, AGRICOLA, and CAB Abstracts databases for literature published during 1997-2013. Studies reporting serological evidence of human influenza A(H9N2) infection among avian-exposed populations were included. We used a World Health Organization (WHO)-recommended case definition for serological evidence of infection based on results of hemagglutination inhibition (HI) and microneutralization (MN) assays. We calculated overall seroprevalence through a random effects meta-analysis model.ResultsSeroprevalence data reported by the studies ranged from 1% to 43% (median, 9%) by HI, which was not significantly different from the seroprevalence estimated through the WHO-recommended case definition (median, 1.3%; range, 0.5%-42.6%). Reported seroprevalence by MN ranged from 0.6% to 9% (median, 2.7%), which was greater than the seroprevalence estimated through the WHO-recommended case definition (median, 0.3%; range, 0.1%-1.4%).ConclusionsA small proportion of avian-exposed humans had evidence of influenza A(H9N2) infection. As the virus has a near global distribution in poultry, it seems likely that present surveillance efforts are missing mild or asymptomatic infections among avian-exposed persons. It seems prudent to closely monitor avian-exposed populations for influenza A(H9N2) infection to provide prepandemic warnings.© The Author 2015. Published by Oxford University Press on behalf of the Infectious Diseases Society of America. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.

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