Incidence of acute respiratory infections in Australia.

We used a national survey of 7578 randomly selected respondents in 2008-2009 to identify the period prevalence of acute respiratory infection (ARI) by season and state, and to estimate the incidence of ARI in the Australian community. A case was defined as any episode of cold or flu with at least one of the following symptoms: fever, chills, sore throat, running nose, or cough in the past 4 weeks. Frequency data were weighted to the Australian population. The response rate to the survey was 49%, and 19·9% (1505/7578) of respondents reported an ARI in the previous 4 weeks, which extrapolated to 68·9 million cases [95% confidence interval (CI) 65·1-72·7] of ARI in Australia annually. The incidence was 3·2 (95% CI 3·0-3·4) cases of ARI/person per year, and was highest in young children and lowest in older people. ARI imposes a significant burden on Australian society.