Household transmission of respiratory viruses – assessment of viral, individual and household characteristics in a population study of healthy Australian adults
1 Murdoch Children’s Research Institute & Melbourne School of Population Health, The University of Melbourne, Parkville, Victoria, 3010, Australia
2 School of Paediatrics and Child Health, University of Western Australia & Telethon Institute for Child Health Research, Princess Margaret Hospital, Perth, WA, Australia
3 Queensland Paediatric Infectious Diseases Laboratory, Queensland Children’s Medical Research Institute and Sir Albert Sakzewski Virus Research Centre, Queensland Children’s Health Services, University of Queensland, Queensland, Australia
4 Clinical Research and Development, CSL Limited, Victoria, Australia
BMC Infectious Diseases 2012, 12:345 doi:10.1186/1471-2334-12-345Published: 11 December 2012
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.
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.
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)).
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.