title: Household transmission of respiratory viruses - assessment of viral, individual and household characteristics in a population study of healthy Australian adults.
abstract: BACKGROUND
  Household transmission of influenza-like illness (ILI) may vary with viral and demographic characteristics. We examined the effect of these factors in a population-based sample of adults with ILI.
  
  
  METHODS
  We conducted a prospective cohort study in community-dwelling Australian adults nested within an influenza vaccine effectiveness trial. On presentation with ILI, participants were swabbed for a range of respiratory viruses and asked to return a questionnaire collecting details of household members with or without similar symptoms. We used logistic and Poisson regression to assess the key characteristics of household transmission.
  
  
  RESULTS
  258 participants from multi-occupancy households experienced 279 ILI episodes and returned a questionnaire. Of these, 183 were the primary case in the household allowing assessment of factors associated with transmission. Transmission was significantly associated in univariate analyses with female sex (27% vs. 13%, risk ratio (RR) = 2.13 (1.08, 4.21)) and the presence of a child in the house (33% vs. 17%, RR = 1.90 (1.11, 3.26)). The secondary household attack proportion (SHAP) was 0.14, higher if influenza was isolated (RR = 2.1 (1.0, 4.5)). Vaccinated participants who nonetheless became infected with influenza had a higher SHAP (Incidence RR = 5.24 (2.17, 12.6)).
  
  
  CONCLUSIONS
  The increased SHAP in households of vaccinated participants who nonetheless had confirmed influenza infection supports the hypothesis that in years of vaccine mismatch, not only is influenza vaccine less protective for the vaccine recipient, but that the population's immunity is also lower.
authors.affiliation: Murdoch Children's Research Institute & Melbourne School of Population Health, The University of Melbourne, Parkville, Victoria, 3010, Australia. jamesm@unimelb.edu.au
authors.forename: James M
authors.initials: JM
authors.lastname: McCaw
authors.forename: Peter F
authors.initials: PF
authors.lastname: Howard
authors.forename: Peter C
authors.initials: PC
authors.lastname: Richmond
authors.forename: Michael
authors.initials: M
authors.lastname: Nissen
authors.forename: Theo
authors.initials: T
authors.lastname: Sloots
authors.forename: Stephen B
authors.initials: SB
authors.lastname: Lambert
authors.forename: Michael
authors.initials: M
authors.lastname: Lai
authors.forename: Michael
authors.initials: M
authors.lastname: Greenberg
authors.forename: Terry
authors.initials: T
authors.lastname: Nolan
authors.forename: Jodie
authors.initials: J
authors.lastname: McVernon
mesh_terms: D000293:Adolescent; D000328:Adult; D001315:Australia / Q000453:epidemiology; D015331:Cohort Studies; D005191:Family Characteristics; D005192:Family Health; D005260:Female; D006801:Humans; D007252:Influenza Vaccines / Q000008:administration & dosage / Q000009:adverse effects; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D012137:Respiratory System / Q000821:virology*; D012141:Respiratory Tract Infections / Q000635:transmission* / Q000821:virology*; D011795:Surveys and Questionnaires; D014777:Virus Diseases / Q000276:immunology* / Q000635:transmission; D055815:Young Adult
chemical_list: D007252:Influenza Vaccines