The risk for pandemic (H1N1) 2009 virus infection increased with the number of children <18 years of age living in the participant's household, which has previously been reported as a risk factor (12) . In Victoria, the median age of persons with reported pandemic (H1N1) 2009 virus infection was 15 years, with 67% of all notifi ed casepatients being 5-17 years of age (1). Miller et al. also found that children were predominantly infected (17) . This fi nding, coupled with the diffi culties of maintaining good respiratory etiquette in young children, is a plausible explanation for the effect of child number on infection risk.