Impact of medical and behavioural factors on influenza-like illness, healthcare-seeking, and antiviral treatment during the 2009 H1N1 pandemic: USA, 2009–2010

We analysed a cross-sectional telephone survey of U.S. adults to assess the impact of selected characteristics on healthcare-seeking behaviours and treatment practices of people with influenza-like illness (ILI) from September 2009 to March 2010. Of 216,431 respondents, 8.1% reported ILI. After adjusting for selected characteristics, respondents aged 18-64 years with the following factors were more likely to report ILI: a diagnosis of asthma [adjusted odds ratio (aOR) 1.88, 95% CI 1.67-2.13] or heart disease (aOR 1.41, 95% CI 1.17-1.70), being disabled (aOR 1.75, 95% CI 1.57-1.96), and reporting financial barriers to healthcare access (aOR 1.63, 95% CI 1.45-1.82). Similar associations were seen in respondents aged ≥ 65 years. Forty percent of respondents with ILI sought healthcare, and 14% who sought healthcare reported receiving influenza antiviral treatment. Treatment was not more frequent in patients with high-risk conditions, except those aged 18-64 years with heart disease (aOR 1.90, 95% CI 1.03-3.51). Of patients at high risk for influenza complications, self-reported ILI was greater but receipt of antiviral treatment was not, despite guidelines recommending their use in this population.