title: [Factors associated with household transmission of influenza (H1N1) 2009].
abstract: BACKGROUND
  A good part of the transmission of influenza occurs in the household context. The main objective of this study was to evaluate the factors associated with the index cases generating secondary cases in household.
  
  
  METHODS
  We designed an observational, retrospective, multicenter through the implementation of a telephone survey in three regions of Spain. The study population were hospitalized and outpatient cases of confirmed H1N1 (2009) reported to the surveillance units from week 44 of 2009. We calculated the secondary attack rate within the household (TAI) and confidence interval of 95%. Factors associated with household transmission were analyzed by logistic regression, calculating odds ratios and confidence intervals at 95%.
  
  
  RESULTS
  the secondary attack rate was 11.3% (95% CI 9.9 to 12.7) within the household. The number of household contacts was the main factor associated with the transmission (OR: 5,02 CI95% 1,78-14,13).
  
  
  CONCLUSIONS
  The factor most associated with the generation of secondary cases is the family size, being greater the larger the group of cohabiting, which is consistent with the data provided by WHO.
authors.affiliation: Centro de Investigación Biomédica en Red de Epidemiología y Salud Pública, Plaza Leseps 1, Barcelona. hvargas@aspb.cat
authors.forename: Hernán
authors.initials: H
authors.lastname: Vargas-Leguas
authors.forename: Joan A
authors.initials: JA
authors.lastname: Caylà
authors.forename: Isabel
authors.initials: I
authors.lastname: Ballester
authors.forename: Rosana
authors.initials: R
authors.lastname: Burgui
authors.forename: Maite
authors.initials: M
authors.lastname: Morteruel
authors.forename: Olivia
authors.initials: O
authors.lastname: Horna
authors.forename: Juan
authors.initials: J
authors.lastname: Bellido
authors.forename: Jesús
authors.initials: J
authors.lastname: Castilla
authors.forename: Anna
authors.initials: A
authors.lastname: Martínez
authors.forename: Pere
authors.initials: P
authors.lastname: Godoy
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D002648:Child; D002675:Child, Preschool; D005192:Family Health; D005260:Female; D006801:Humans; D007223:Infant; D053118:Influenza A Virus, H1N1 Subtype; D007251:Influenza, Human / Q000453:epidemiology / Q000635:transmission*; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D055815:Young Adult