title: Epidemiological and virological characteristics of pandemic influenza A (H1N1) school outbreaks in China in 2009.
abstract: BACKGROUND
  During the 2009 pandemic influenza H1N1 (2009) virus (pH1N1) outbreak, school students were at an increased risk of infection by the pH1N1 virus. However, the estimation of the attack rate showed significant variability.
  
  
  METHODS
  Two school outbreaks were investigated in this study. A questionnaire was designed to collect information by interview. Throat samples were collected from all the subjects in this study 6 times and sero samples 3 times to confirm the infection and to determine viral shedding. Data analysis was performed using the software STATA 9.0.
  
  
  RESULTS
  The attack rate of the pH1N1 outbreak was 58.3% for the primary school, and 52.9% for the middle school. The asymptomatic infection rates of the two schools were 35.8% and 37.6% respectively. Peak virus shedding occurred on the day of ARI symptoms onset, followed by a steady decrease over subsequent days (p = 0.026). No difference was found either in viral shedding or HI titer between the symptomatic and the asymptomatic infectious groups.
  
  
  CONCLUSIONS
  School children were found to be at a high risk of infection by the novel virus. This may be because of a heightened risk of transmission owing to increased mixing at boarding school, or a lack of immunity owing to socio-economic status. We conclude that asymptomatically infectious cases may play an important role in transmission of the pH1N1 virus.
authors.affiliation: State Key Laboratory for Molecular Virology and Genetic Engineering, National Institute for Viral Disease Control and Prevention, Chinese Center for Disease Control and Prevention, Beijing, China.
authors.forename: Lei
authors.initials: L
authors.lastname: Yan
authors.forename: Yan
authors.initials: Y
authors.lastname: Gao
authors.forename: Yong
authors.initials: Y
authors.lastname: Zhang
authors.forename: Michael
authors.initials: M
authors.lastname: Tildesley
authors.forename: Liqi
authors.initials: L
authors.lastname: Liu
authors.forename: Ye
authors.initials: Y
authors.lastname: Zhang
authors.forename: Leying
authors.initials: L
authors.lastname: Wen
authors.forename: Wei
authors.initials: W
authors.lastname: Wang
authors.forename: Xiaodan
authors.initials: X
authors.lastname: Li
authors.forename: Ying
authors.initials: Y
authors.lastname: Hu
authors.forename: Tian
authors.initials: T
authors.lastname: Bai
authors.forename: Min
authors.initials: M
authors.lastname: Wang
authors.forename: Yuhong
authors.initials: Y
authors.lastname: Zeng
authors.forename: Dingming
authors.initials: D
authors.lastname: Wang
authors.forename: Xianjun
authors.initials: X
authors.lastname: Wang
authors.forename: Yu
authors.initials: Y
authors.lastname: Lan
authors.forename: Shiwen
authors.initials: S
authors.lastname: Wang
authors.forename: Yuelong
authors.initials: Y
authors.lastname: Shu
mesh_terms: D000293:Adolescent; D058345:Asymptomatic Infections / Q000453:epidemiology; D002648:Child; D002681:China / Q000453:epidemiology; D004196:Disease Outbreaks; D005260:Female; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype / Q000502:physiology*; D007251:Influenza, Human / Q000453:epidemiology* / Q000821:virology; D008297:Male; D058873:Pandemics; D012307:Risk Factors; D012574:Schools; D011795:Surveys and Questionnaires; D019562:Viral Load; D017201:Virus Shedding