title: [Epidemiological characteristics of 420 influenza A (H1N1) cases confirmed in the early stage of the epidemic in mainland China].
abstract: OBJECTIVE
  To describe the epidemical characteristics of A (H1N1) influenza identified in the early stage (from May 11 to June 22, 2009) of the epidemic, in mainland China.
  
  
  METHODS
  Epidemical characteristics of 420 confirmed A (H1N1) influenza cases reported from May 11 to June 22, 2009 were analyzed descriptively, including the distribution of age, sex, source of infection, main symptoms and incubation period.
  
  
  RESULTS
  A total of 77.8% early cases in mainland China were imported from other countries. Three countries including America, Canada and Australia were attributed to 90% of the imported cases. Most of the cases were from 6 months to 73 years old, with 94% of them under 50 years. Most of the symptoms would include fever (81%), cough (40%) and sore throat (35%). The mean incubation period of second-generation cases was 4.3 (4.2 +/- 1.5) days.
  
  
  CONCLUSIONS
  Imported cases dominated the total cases in the early stage of the epidemic had similar gender distribution of those from exporting countries. Fever, cough and sore throat were the three main symptoms manifested in influenza cases. 2.5 +/- 1.9 (1 - 11) days was found in imported cases between the day of off-board and the onset of symptoms. The incubation period was 4.3 +/- 1.7 (1 - 8) days among the secondary cases.
authors.affiliation: State Key Laboratory of Pathogen and Biosecurity, Academy of Military Medical Science Institute of Microbiology and Epidemiology, Beijing 100071, China.
authors.forename: Ya-pin
authors.initials: YP
authors.lastname: Li
authors.forename: Quan
authors.initials: Q
authors.lastname: Qian
authors.forename: Li-qun
authors.initials: LQ
authors.lastname: Fang
authors.forename: Hong
authors.initials: H
authors.lastname: Yang
authors.forename: Mao-ti
authors.initials: MT
authors.lastname: Wei
authors.forename: Yan
authors.initials: Y
authors.lastname: Gao
authors.forename: Hua
authors.initials: H
authors.lastname: Yang
authors.forename: Yong
authors.initials: Y
authors.lastname: Zhang
authors.forename: Wu-chun
authors.initials: WC
authors.lastname: Cao
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D002648:Child; D002675:Child, Preschool; D002681:China / Q000453:epidemiology; D005260:Female; D006801:Humans; D007223:Infant; D053118:Influenza A Virus, H1N1 Subtype; D007251:Influenza, Human / Q000175:diagnosis / Q000453:epidemiology* / Q000821:virology; D008297:Male; D008875:Middle Aged; D055815:Young Adult