title: Epidemiology of human infections with avian influenza A(H7N9) virus in China.
abstract: BACKGROUND
  The first identified cases of avian influenza A(H7N9) virus infection in humans occurred in China during February and March 2013. We analyzed data obtained from field investigations to describe the epidemiologic characteristics of H7N9 cases in China identified as of December 1, 2013.
  
  
  METHODS
  Field investigations were conducted for each confirmed case of H7N9 virus infection. A patient was considered to have a confirmed case if the presence of the H7N9 virus was verified by means of real-time reverse-transcriptase-polymerase-chain-reaction assay (RT-PCR), viral isolation, or serologic testing. Information on demographic characteristics, exposure history, and illness timelines was obtained from patients with confirmed cases. Close contacts were monitored for 7 days for symptoms of illness. Throat swabs were obtained from contacts in whom symptoms developed and were tested for the presence of the H7N9 virus by means of real-time RT-PCR.
  
  
  RESULTS
  Among 139 persons with confirmed H7N9 virus infection, the median age was 61 years (range, 2 to 91), 71% were male, and 73% were urban residents. Confirmed cases occurred in 12 areas of China. Nine persons were poultry workers, and of 131 persons with available data, 82% had a history of exposure to live animals, including chickens (82%). A total of 137 persons (99%) were hospitalized, 125 (90%) had pneumonia or respiratory failure, and 65 of 103 with available data (63%) were admitted to an intensive care unit. A total of 47 persons (34%) died in the hospital after a median duration of illness of 21 days, 88 were discharged from the hospital, and 2 remain hospitalized in critical condition; 2 patients were not admitted to a hospital. In four family clusters, human-to-human transmission of H7N9 virus could not be ruled out. Excluding secondary cases in clusters, 2675 close contacts of case patients completed the monitoring period; respiratory symptoms developed in 28 of them (1%); all tested negative for H7N9 virus.
  
  
  CONCLUSIONS
  Most persons with confirmed H7N9 virus infection had severe lower respiratory tract illness, were epidemiologically unrelated, and had a history of recent exposure to poultry. However, limited, nonsustained human-to-human H7N9 virus transmission could not be ruled out in four families.
authors.affiliation: The authors' affiliations are listed in the Appendix.
authors.forename: Qun
authors.initials: Q
authors.lastname: Li
authors.forename: Lei
authors.initials: L
authors.lastname: Zhou
authors.forename: Minghao
authors.initials: M
authors.lastname: Zhou
authors.forename: Zhiping
authors.initials: Z
authors.lastname: Chen
authors.forename: Furong
authors.initials: F
authors.lastname: Li
authors.forename: Huanyu
authors.initials: H
authors.lastname: Wu
authors.forename: Nijuan
authors.initials: N
authors.lastname: Xiang
authors.forename: Enfu
authors.initials: E
authors.lastname: Chen
authors.forename: Fenyang
authors.initials: F
authors.lastname: Tang
authors.forename: Dayan
authors.initials: D
authors.lastname: Wang
authors.forename: Ling
authors.initials: L
authors.lastname: Meng
authors.forename: Zhiheng
authors.initials: Z
authors.lastname: Hong
authors.forename: Wenxiao
authors.initials: W
authors.lastname: Tu
authors.forename: Yang
authors.initials: Y
authors.lastname: Cao
authors.forename: Leilei
authors.initials: L
authors.lastname: Li
authors.forename: Fan
authors.initials: F
authors.lastname: Ding
authors.forename: Bo
authors.initials: B
authors.lastname: Liu
authors.forename: Mei
authors.initials: M
authors.lastname: Wang
authors.forename: Rongheng
authors.initials: R
authors.lastname: Xie
authors.forename: Rongbao
authors.initials: R
authors.lastname: Gao
authors.forename: Xiaodan
authors.initials: X
authors.lastname: Li
authors.forename: Tian
authors.initials: T
authors.lastname: Bai
authors.forename: Shumei
authors.initials: S
authors.lastname: Zou
authors.forename: Jun
authors.initials: J
authors.lastname: He
authors.forename: Jiayu
authors.initials: J
authors.lastname: Hu
authors.forename: Yangting
authors.initials: Y
authors.lastname: Xu
authors.forename: Chengliang
authors.initials: C
authors.lastname: Chai
authors.forename: Shiwen
authors.initials: S
authors.lastname: Wang
authors.forename: Yongjun
authors.initials: Y
authors.lastname: Gao
authors.forename: Lianmei
authors.initials: L
authors.lastname: Jin
authors.forename: Yanping
authors.initials: Y
authors.lastname: Zhang
authors.forename: Huiming
authors.initials: H
authors.lastname: Luo
authors.forename: Hongjie
authors.initials: H
authors.lastname: Yu
authors.forename: Jianfeng
authors.initials: J
authors.lastname: He
authors.forename: Qi
authors.initials: Q
authors.lastname: Li
authors.forename: Xianjun
authors.initials: X
authors.lastname: Wang
authors.forename: Lidong
authors.initials: L
authors.lastname: Gao
authors.forename: Xinghuo
authors.initials: X
authors.lastname: Pang
authors.forename: Guohua
authors.initials: G
authors.lastname: Liu
authors.forename: Yansheng
authors.initials: Y
authors.lastname: Yan
authors.forename: Hui
authors.initials: H
authors.lastname: Yuan
authors.forename: Yuelong
authors.initials: Y
authors.lastname: Shu
authors.forename: Weizhong
authors.initials: W
authors.lastname: Yang
authors.forename: Yu
authors.initials: Y
authors.lastname: Wang
authors.forename: Fan
authors.initials: F
authors.lastname: Wu
authors.forename: Timothy M
authors.initials: TM
authors.lastname: Uyeki
authors.forename: Zijian
authors.initials: Z
authors.lastname: Feng
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000818:Animals; D002648:Child; D002675:Child, Preschool; D002681:China / Q000453:epidemiology; D005190:Family; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D064766:Influenza A Virus, H7N9 Subtype; D005585:Influenza in Birds / Q000635:transmission; D007251:Influenza, Human / Q000453:epidemiology* / Q000635:transmission / Q000821:virology; D008297:Male; D008875:Middle Aged; D011024:Pneumonia, Viral / Q000453:epidemiology* / Q000821:virology; D011200:Poultry