title: The effect of age on transmission of 2009 pandemic influenza A (H1N1) in a camp and associated households.
abstract: BACKGROUND
  A major portion of influenza disease burden during the 2009 pandemic was observed among young people.
  
  
  METHODS
  We examined the effect of age on the transmission of influenza-like illness associated with the 2009 pandemic influenza A (H1N1) virus (pH1N1) for an April-May 2009 outbreak among youth-camp participants and household contacts in Washington State.
  
  
  RESULTS
  An influenza-like illness attack rate of 51% was found among 96 camp participants. We observed a cabin secondary attack rate of 42% (95% confidence interval = 21%-66%) and a camp local reproductive number of 2.7 (1.7-4.1) for influenza-like illness among children (less than 18 years old). Among the 136 contacts in the 41 households with an influenza-like illness index case who attended the camp, the influenza-like illness secondary attack rate was 11% for children (5%-21%) and 4% for adults (2%-8%). The odds ratio for influenza-like illness among children versus adults was 3.1 (1.3-7.3).
  
  
  CONCLUSIONS
  The strong age effect, combined with the low number of susceptible children per household (1.2), plausibly explains the lower-than-expected household secondary attack rate for influenza-like illness, illustrating the importance of other venues where children congregate for sustaining community transmission. Quantifying the effects of age on pH1N1 transmission is important for informing effective intervention strategies.
authors.affiliation: Center for Statistics and Quantitative Infectious Disease, Vaccine and Infectious Disease Institute, Fred Hutchinson Cancer Research Center, Seattle, WA, USA.
authors.forename: Jonathan D
authors.initials: JD
authors.lastname: Sugimoto
authors.forename: Nagesh N
authors.initials: NN
authors.lastname: Borse
authors.forename: Myduc L
authors.initials: ML
authors.lastname: Ta
authors.forename: Lauren J
authors.initials: LJ
authors.lastname: Stockman
authors.forename: Gayle E
authors.initials: GE
authors.lastname: Fischer
authors.forename: Yang
authors.initials: Y
authors.lastname: Yang
authors.forename: M Elizabeth
authors.initials: ME
authors.lastname: Halloran
authors.forename: Ira M
authors.initials: IM
authors.lastname: Longini
authors.forename: Jeffrey S
authors.initials: JS
authors.lastname: Duchin
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D002165:Camping; D005260:Female; D006306:Health Surveys; D006798:Housing; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype / Q000302:isolation & purification*; D007251:Influenza, Human / Q000453:epidemiology* / Q000635:transmission*; D008297:Male; D015233:Models, Statistical; D058873:Pandemics; D012189:Retrospective Studies; D014861:Washington / Q000453:epidemiology; D055815:Young Adult