Open Access Highly Accessed Research article

Household transmission of respiratory viruses – assessment of viral, individual and household characteristics in a population study of healthy Australian adults

James M McCaw1*, Peter F Howard1, Peter C Richmond2, Michael Nissen3, Theo Sloots3, Stephen B Lambert3, Michael Lai4, Michael Greenberg4, Terry Nolan1 and Jodie McVernon1

Author affiliations

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

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Citation and License

BMC Infectious Diseases 2012, 12:345  doi:10.1186/1471-2334-12-345

Published: 11 December 2012

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.

Keywords:
Epidemiology; Transmission; Influenza, human; Influenza vaccines; Respiratory tract infection