title: Household transmission of 2009 pandemic influenza A (H1N1): a systematic review and meta-analysis.
abstract: BACKGROUND
  During the 2009 influenza A (H1N1) pandemic, household transmission studies were implemented to better understand the characteristics of the transmission of the novel virus in a confined setting.
  
  
  METHODS
  We conducted a systematic review and meta-analysis to assess and summarize the findings of these studies. We identified 27 articles, around half of which reported studies conducted in May and June 2009.
  
  
  RESULTS
  In 13 of the 27 studies (48%) that collected respiratory specimens from household contacts, point estimates of the risk of secondary infection ranged from 3% to 38%, with substantial heterogeneity. Meta-regression analyses revealed that a part of the heterogeneity reflected varying case ascertainment and study designs. The estimates of symptomatic secondary infection risk, based on 20 studies identifying febrile acute respiratory illness among household contacts, also showed substantial variability, with point estimates ranging from 4% to 37%.
  
  
  CONCLUSIONS
  Transmission of the 2009 pandemic virus in households appeared to vary among countries and settings, with differences in estimates of the secondary infection risk also partly due to differences in study designs.
authors.affiliation: School of Public Health, The University of Hong Kong, Pokfulam, Hong Kong Special Administrative Region, China.
authors.forename: Lincoln L H
authors.initials: LL
authors.lastname: Lau
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Nishiura
authors.forename: Heath
authors.initials: H
authors.lastname: Kelly
authors.forename: Dennis K M
authors.initials: DK
authors.lastname: Ip
authors.forename: Gabriel M
authors.initials: GM
authors.lastname: Leung
authors.forename: Benjamin J
authors.initials: BJ
authors.lastname: Cowling
mesh_terms: D016358:Contact Tracing; D005191:Family Characteristics; D014943:Global Health; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype / Q000302:isolation & purification; D007251:Influenza, Human / Q000175:diagnosis / Q000453:epidemiology / Q000635:transmission*; D058873:Pandemics; D011159:Population Surveillance; D012044:Regression Analysis; D012306:Risk