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

Epidemiology and Prevention Branch, Influenza Division, National Center for Immunization and Respiratory Disease, Centers for Disease Control and Prevention, Atlanta, GA, USA.
Epidemiology and Infection (Impact Factor: 2.54). 03/2013; 142(1):1-12. DOI: 10.1017/S0950268813000654
Source: PubMed


SUMMARY 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.

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    • "Additionally Flusurvey participants are more likely to be from London, be female, have risk factors and be vaccinated than the UK general population. Other methods such as telephone surveillance can be used to overcome these limitations [15,24], however these surveillance techniques are more expensive, time absorbing, have representativeness problems of their own, and still have the problem of self-reports of ILI. "
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    ABSTRACT: Background Influenza and Influenza-like-illness (ILI) represents a substantial public health problem, but it is difficult to measure the overall burden as many cases do not access health care. Community cohorts have the advantage of not requiring individuals to present at hospitals and surgeries and therefore can potentially monitor a wider variety of cases. This study reports on the incidence and risk factors for ILI in the UK as measured using Flusurvey, an internet-based open community cohort. Methods Upon initial online registration participants were asked background characteristics, and every week were asked to complete a symptoms survey. We compared the representativeness of our sample to the overall population. We used two case definitions of ILI, which differed in whether fever/chills was essential. We calculated ILI incidence week by week throughout the season, and investigated risk factors associated with ever reporting ILI over the course of the season. Risk factor analysis was conducted using binomial regression. Results 5943 participants joined the survey, and 4532 completed the symptoms survey at least twice. Participants who filled in symptoms surveys at least twice filled in a median of nine symptoms surveys over the course of the study. 46.1% of participants reported at least one episode of ILI, and 6.0% of all reports were positive for ILI. Females had slightly higher incidence, and individuals over 65 had the lowest incidence. Incidence peaked just before Christmas and declined dramatically during school holidays. Multivariate regression showed that, for both definitions of ILI considered, being female, unvaccinated, having underlying health issues, having contact with children, being aged between 35 and 64, and being a smoker were associated with the highest risk of reporting an ILI. The use of public transport was not associated with an increased risk of ILI. Conclusions Our results show that internet based surveillance can be used to measure ILI and understand risk factors. Vaccination is shown to be linked to a reduced risk of reporting ILI. Taking public transport does not increase the risk of reporting ILI. Flusurvey and other participatory surveillance techniques can be used to provide reliable information to policy makers in nearly real-time.
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