title: A Systematic Review and Meta-Analysis of the Seroprevalence of Influenza A(H9N2) Infection Among Humans.
abstract: BACKGROUND
  Given 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.
  
  
  METHODS
  We 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.
  
  
  RESULTS
  Seroprevalence 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%).
  
  
  CONCLUSIONS
  A 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.
authors.affiliation: Department of Environmental and Global Health, College of Public Health and Health Professions Emerging Pathogens Institute, University of Florida, Gainesville.
authors.forename: Salah Uddin
authors.initials: SU
authors.lastname: Khan
authors.affiliation: Department of Environmental and Global Health, College of Public Health and Health Professions Emerging Pathogens Institute, University of Florida, Gainesville Division of Infectious Diseases, Global Health Institute, & Nicholas School of the Environment, Duke University, Durham, North Carolina Laboratory of One Health Research, Program in Emerging Infectious Diseases, Duke-NUS Graduate Medical School, Singapore.
authors.forename: Benjamin D
authors.initials: BD
authors.lastname: Anderson
authors.affiliation: Department of Environmental and Global Health, College of Public Health and Health Professions Emerging Pathogens Institute, University of Florida, Gainesville.
authors.forename: Gary L
authors.initials: GL
authors.lastname: Heil
authors.affiliation: Department of Environmental and Global Health, College of Public Health and Health Professions Emerging Pathogens Institute, University of Florida, Gainesville.
authors.forename: Song
authors.initials: S
authors.lastname: Liang
authors.affiliation: Division of Infectious Diseases, Global Health Institute, & Nicholas School of the Environment, Duke University, Durham, North Carolina Laboratory of One Health Research, Program in Emerging Infectious Diseases, Duke-NUS Graduate Medical School, Singapore.
authors.forename: Gregory C
authors.initials: GC
authors.lastname: Gray
mesh_terms: D000818:Animals; D000914:Antibodies, Viral / Q000097:blood; D006801:Humans; D053127:Influenza A Virus, H9N2 Subtype / Q000276:immunology*; D007251:Influenza, Human / Q000453:epidemiology* / Q000276:immunology / Q000821:virology; D016036:Seroepidemiologic Studies; D015047:Zoonoses
chemical_list: D000914:Antibodies, Viral
keywords: H9N2 subtype; hemagglutination inhibition test; influenza A virus; meta-analysis; microneutralization test; seroprevalence; systematic review