title: Risk factors for influenza A(H7N9) disease--China, 2013.
abstract: BACKGROUND
  The majority of human cases of novel avian influenza A(H7N9), which emerged in China in spring 2013, include reported exposure to poultry. However, specific host and exposure risk factors for disease are unknown, yet critical to design prevention measures.
  
  
  METHODS
  In April-June 2013, we conducted a case-control study in 8 Chinese provinces. Patients with laboratory-confirmed A(H7N9) (n = 89) were matched by age, sex, and neighborhood to controls (n = 339). Subjects completed a questionnaire on medical history and potential exposures, including poultry markets and other poultry exposure. We used conditional logistic regression to calculate matched and adjusted odds ratios (ORs) for the association of A(H7N9) virus infection with potential risk factors.
  
  
  RESULTS
  Fifty-five percent of patients compared with 31% of controls reported any contact with poultry (matched OR [mOR], 7.8; 95% confidence interval [CI], 3.3-18.8). Sixty-seven percent of patients compared with 35% of controls visited a live poultry market (mOR, 5.4; CI, 3.0-9.7). Visiting live poultry markets increased risk of infection even after adjusting for poultry contact and other confounders (adjusted OR, 3.4; CI, 1.8-6.7). Backyard poultry were not associated with increased risk; 14% of cases did not report any poultry exposure or market visit. Obesity (mOR, 4.7; CI, 1.8-12.4), chronic obstructive pulmonary disease (mOR, 2.7; CI, 1.1-6.9), and immunosuppressive medications (mOR, 9.0; CI, 1.7-47.2) were associated with A(H7N9) disease.
  
  
  CONCLUSIONS
  Exposures to poultry in markets were associated with A(H7N9) virus infection, even without poultry contact. China should consider permanently closing live poultry markets or aggressively pursuing control measures to prevent spread of this emerging pathogen.
authors.affiliation: Public Health Emergency Center, Chinese Center for Disease Control and Prevention, Beijing.
authors.forename: Bo
authors.initials: B
authors.lastname: Liu
authors.affiliation: Epidemic Intelligence Service assigned to the Influenza Division, US Centers for Disease Control and Prevention, Atlanta, Georgia.
authors.forename: Fiona
authors.initials: F
authors.lastname: Havers
authors.affiliation: Influenza Division, Zhejiang Provincial Center for Disease Control and Prevention, Hangzhou.
authors.forename: Enfu
authors.initials: E
authors.lastname: Chen
authors.affiliation: Shanghai Municipal Center for Disease Control and Prevention.
authors.forename: Zhengan
authors.initials: Z
authors.lastname: Yuan
authors.affiliation: Jiangxi Provincial Center for Disease Control and Prevention, Nanchang.
authors.forename: Hui
authors.initials: H
authors.lastname: Yuan
authors.affiliation: Fujian Provincial Center for Disease Control and Prevention, Fuzhou.
authors.forename: Jianming
authors.initials: J
authors.lastname: Ou
authors.affiliation: China Office, US Centers for Disease Control and Prevention, Beijing.
authors.forename: Mei
authors.initials: M
authors.lastname: Shang
authors.affiliation: Henan Provincial Center for Disease Control and Prevention, Zhengzhou.
authors.forename: Kai
authors.initials: K
authors.lastname: Kang
authors.affiliation: Public Health Emergency Center, Chinese Center for Disease Control and Prevention, Beijing.
authors.forename: Kaiju
authors.initials: K
authors.lastname: Liao
authors.affiliation: Hunan Provincial Center for Disease Control and Prevention, Changsha.
authors.forename: Fuqiang
authors.initials: F
authors.lastname: Liu
authors.affiliation: Public Health Emergency Center, Chinese Center for Disease Control and Prevention, Beijing.
authors.forename: Dan
authors.initials: D
authors.lastname: Li
authors.affiliation: Zhejiang Hangzhou Center for Disease Control and Prevention, Hangzhou.
authors.forename: Hua
authors.initials: H
authors.lastname: Ding
authors.affiliation: Public Health Emergency Center, Chinese Center for Disease Control and Prevention, Beijing.
authors.forename: Lei
authors.initials: L
authors.lastname: Zhou
authors.affiliation: Shanghai Pudong New Area Center for Disease Control and Prevention, Shanghai.
authors.forename: Weiping
authors.initials: W
authors.lastname: Zhu
authors.affiliation: Public Health Emergency Center, Chinese Center for Disease Control and Prevention, Beijing.
authors.forename: Fan
authors.initials: F
authors.lastname: Ding
authors.affiliation: Zhejiang Huzhou Center for Disease Control and Prevention, Hangzhou.
authors.forename: Peng
authors.initials: P
authors.lastname: Zhang
authors.affiliation: Public Health Emergency Center, Chinese Center for Disease Control and Prevention, Beijing.
authors.forename: Xiaoye
authors.initials: X
authors.lastname: Wang
authors.affiliation: Public Health Emergency Center, Chinese Center for Disease Control and Prevention, Beijing.
authors.forename: Jianyi
authors.initials: J
authors.lastname: Yao
authors.affiliation: Public Health Emergency Center, Chinese Center for Disease Control and Prevention, Beijing.
authors.forename: Nijuan
authors.initials: N
authors.lastname: Xiang
authors.affiliation: China Office, US Centers for Disease Control and Prevention, Beijing.
authors.forename: Suizan
authors.initials: S
authors.lastname: Zhou
authors.affiliation: Jiangxi Provincial Center for Disease Control and Prevention, Nanchang.
authors.forename: Xiaoqin
authors.initials: X
authors.lastname: Liu
authors.affiliation: China Office, US Centers for Disease Control and Prevention, Beijing.
authors.forename: Ying
authors.initials: Y
authors.lastname: Song
authors.affiliation: Shanghai Minhang District Center for Disease Control and Prevention.
authors.forename: Hualin
authors.initials: H
authors.lastname: Su
authors.affiliation: Public Health Emergency Center, Chinese Center for Disease Control and Prevention, Beijing.
authors.forename: Rui
authors.initials: R
authors.lastname: Wang
authors.affiliation: Influenza Division, Zhejiang Provincial Center for Disease Control and Prevention, Hangzhou.
authors.forename: Jian
authors.initials: J
authors.lastname: Cai
authors.affiliation: Public Health Emergency Center, Chinese Center for Disease Control and Prevention, Beijing.
authors.forename: Yang
authors.initials: Y
authors.lastname: Cao
authors.affiliation: Shandong Provincial Center for Disease Control and Prevention, Jinan City.
authors.forename: Xianjun
authors.initials: X
authors.lastname: Wang
authors.affiliation: Institute for Viral Disease Control and Prevention, Chinese Center for Disease Control and Prevention, Beijing.
authors.forename: Tian
authors.initials: T
authors.lastname: Bai
authors.affiliation: Anhui Provincial Center for Disease Control and Prevention, Hefei, China.
authors.forename: Jianjun
authors.initials: J
authors.lastname: Wang
authors.affiliation: Public Health Emergency Center, Chinese Center for Disease Control and Prevention, Beijing.
authors.forename: Zijian
authors.initials: Z
authors.lastname: Feng
authors.affiliation: Public Health Emergency Center, Chinese Center for Disease Control and Prevention, Beijing.
authors.forename: Yanping
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Influenza Division, US Centers for Disease Control and Prevention, Atlanta, Georgia.
authors.forename: Marc-Alain
authors.initials: MA
authors.lastname: Widdowson
authors.affiliation: Public Health Emergency Center, Chinese Center for Disease Control and Prevention, Beijing.
authors.forename: Qun
authors.initials: Q
authors.lastname: Li
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D016022:Case-Control Studies; D002648:Child; D002681:China / Q000453:epidemiology; D005260:Female; D015438:Health Behavior; D049674:History, 21st Century; D006801:Humans; D064766:Influenza A Virus, H7N9 Subtype / Q000235:genetics / Q000276:immunology; D007251:Influenza, Human / Q000453:epidemiology* / Q000266:history; D008297:Male; D008875:Middle Aged; D062486:Public Health Surveillance; D012307:Risk Factors; D016036:Seroepidemiologic Studies; D055815:Young Adult
keywords: China; H7N9; avian influenza; avian influenza A(H7N9) virus