title: Sero-epidemiologic study of influenza A(H7N9) infection among exposed populations, China 2013-2014.
abstract: The 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.
  
  
  
  We assessed the seroprevalence of antibodies to influenza A(H7N9) virus in three populations during the early stages of the epidemic.
  
  
  
  From 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.
  
  
  
  Among 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.
  
  
  
  There 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.
authors.affiliation: Chinese Center for Disease Control and Prevention, Beijing, China.
authors.forename: Nijuan
authors.initials: N
authors.lastname: Xiang
authors.affiliation: National Institute for Viral Disease Control and Prevention, Collaboration Innovation Center for Diagnosis and Treatment of Infectious Diseases, Chinese Center for Disease Control and Prevention, Key Laboratory for Medical Virology, National Health and Family Planning Commission, Beijing, China.
authors.forename: Tian
authors.initials: T
authors.lastname: Bai
authors.affiliation: Henan Provincial Center for Disease Control and Prevention, Zhengzhou, Henan Province, China.
authors.forename: Kai
authors.initials: K
authors.lastname: Kang
authors.affiliation: Jiangxi Provincial Center for Disease Control and Prevention, Nanchang, Jiangxi Province, China.
authors.forename: Hui
authors.initials: H
authors.lastname: Yuan
authors.affiliation: United States Centers for Disease Control and Prevention, Atlanta, GA, USA.
authors.forename: Suizan
authors.initials: S
authors.lastname: Zhou
authors.affiliation: Chinese Center for Disease Control and Prevention, Beijing, China.
authors.forename: Ruiqi
authors.initials: R
authors.lastname: Ren
authors.affiliation: Xinhui District Center for Disease Control and Prevention, Jiangmen, Guangdong Province, China.
authors.forename: Xiuying
authors.initials: X
authors.lastname: Li
authors.affiliation: Anhui Provincial Center for Disease Control and Prevention, Hefei, Anhui Province, China.
authors.forename: Jiabing
authors.initials: J
authors.lastname: Wu
authors.affiliation: Jilin Provincial Center for Disease Control and Prevention, Changchun, Jilin Province, China.
authors.forename: Liquan
authors.initials: L
authors.lastname: Deng
authors.affiliation: Hunan Provincial Center for Disease Control and Prevention, Changsha, Hunan Province, China.
authors.forename: Ge
authors.initials: G
authors.lastname: Zeng
authors.affiliation: Shandong Provincial Center for Disease Control and Prevention, Jinan, Shandong Province, China.
authors.forename: Xianjun
authors.initials: X
authors.lastname: Wang
authors.affiliation: Shanghai Municipal Center for Disease Control and Prevention, Shanghai, China.
authors.forename: Shenghua
authors.initials: S
authors.lastname: Mao
authors.affiliation: Hebei Provincial Center for Disease Control and Prevention, Shijiazhuang, Hebei Province, China.
authors.forename: Jian
authors.initials: J
authors.lastname: Shi
authors.affiliation: National Institute for Viral Disease Control and Prevention, Collaboration Innovation Center for Diagnosis and Treatment of Infectious Diseases, Chinese Center for Disease Control and Prevention, Key Laboratory for Medical Virology, National Health and Family Planning Commission, Beijing, China.
authors.forename: Rongbao
authors.initials: R
authors.lastname: Gao
authors.affiliation: National Institute for Viral Disease Control and Prevention, Collaboration Innovation Center for Diagnosis and Treatment of Infectious Diseases, Chinese Center for Disease Control and Prevention, Key Laboratory for Medical Virology, National Health and Family Planning Commission, Beijing, China.
authors.forename: Tao
authors.initials: T
authors.lastname: Chen
authors.affiliation: National Institute for Viral Disease Control and Prevention, Collaboration Innovation Center for Diagnosis and Treatment of Infectious Diseases, Chinese Center for Disease Control and Prevention, Key Laboratory for Medical Virology, National Health and Family Planning Commission, Beijing, China.
authors.forename: Sumei
authors.initials: S
authors.lastname: Zou
authors.affiliation: Chinese Center for Disease Control and Prevention, Beijing, China.
authors.forename: Dan
authors.initials: D
authors.lastname: Li
authors.affiliation: United States Centers for Disease Control and Prevention, Atlanta, GA, USA.
authors.forename: Fiona
authors.initials: F
authors.lastname: Havers
authors.affiliation: United States Centers for Disease Control and Prevention, Atlanta, GA, USA.
authors.forename: Marc-Alain
authors.initials: MA
authors.lastname: Widdowson
authors.affiliation: United States Centers for Disease Control and Prevention, Atlanta, GA, USA.
authors.forename: Carolyn M
authors.initials: CM
authors.lastname: Greene
authors.affiliation: Chinese Center for Disease Control and Prevention, Beijing, China.
authors.forename: Yanping
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Chinese Center for Disease Control and Prevention, Beijing, China.
authors.forename: Daxin
authors.initials: D
authors.lastname: Ni
authors.affiliation: Jiangxi Provincial Center for Disease Control and Prevention, Nanchang, Jiangxi Province, China.
authors.forename: Xiaoqing
authors.initials: X
authors.lastname: Liu
authors.affiliation: Chinese Center for Disease Control and Prevention, Beijing, China.
authors.forename: Qun
authors.initials: Q
authors.lastname: Li
authors.affiliation: National Institute for Viral Disease Control and Prevention, Collaboration Innovation Center for Diagnosis and Treatment of Infectious Diseases, Chinese Center for Disease Control and Prevention, Key Laboratory for Medical Virology, National Health and Family Planning Commission, Beijing, China.
authors.forename: Yuelong
authors.initials: Y
authors.lastname: Shu
mesh_terms: D000328:Adult; D000818:Animals; D000914:Antibodies, Viral / Q000097:blood*; D002681:China / Q000453:epidemiology; D005260:Female; D006801:Humans; D064766:Influenza A Virus, H7N9 Subtype / Q000276:immunology* / Q000302:isolation & purification; D005585:Influenza in Birds / Q000453:epidemiology; D007251:Influenza, Human / Q000453:epidemiology* / Q000276:immunology / Q000635:transmission / Q000821:virology; D008297:Male; D009976:Orthomyxoviridae Infections / Q000453:epidemiology / Q000276:immunology / Q000821:virology; D011200:Poultry / Q000821:virology; D016036:Seroepidemiologic Studies; D055815:Young Adult
chemical_list: D000914:Antibodies, Viral
keywords: H7N9 virus; avian influenza; close contact; general population; poultry workers; serology