Obesity and Respiratory Hospitalizations During Influenza Seasons in Ontario, Canada: A Cohort Study

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Abstract
(See the Editorial Commentary by Jain and Chaves, on pages 422–424 .) Background. Previous studies suggest that obesity may be a risk factor for complications from pandemic influenza A(H1N1) infection. We aimed to examine the association between obesity and respiratory hospitalizations during seasonal influenza epidemics and to determine the extent of this association among individuals without established risk factors for serious complications due to influenza infection. Methods. We conducted a cohort study over 12 influenza seasons (1996–1997 through 2007–2008) of 82545 respondents to population health surveys in Ontario, Canada. We included individuals aged 18–64 years who had responded to a survey within 5 years prior to the start of an influenza season. We used logistic regression to examine the association between self-reported body mass index (BMI) and hospitalization for selected respiratory diseases (pneumonia and influenza, acute respiratory diseases, and chronic lung diseases), both in the entire cohort and stratified by chronic condition status. Results. Obese class I (BMI, 30–34.9) (odds ratio [OR], 1.45 [95% confidence interval {CI}, 1.03–2.05]) and obese class II or III (BMI, ≥35) individuals (OR, 2.12 [95% CI, 1.45–3.10]) were more likely than normal weight individuals to have a respiratory hospitalization during influenza seasons. Among obese class II or III individuals, the association was present both for those without previously identified risk factors (OR, 5.10 [95% CI, 2.53–10.24]) and for those with 1 risk factor (OR, 2.11 [95% CI, 1.10–4.06]). Conclusions. Severely obese individuals with and without chronic conditions are at increased risk for respiratory hospitalizations during influenza seasons. They should be considered a priority group for preventive influenza measures, such as vaccination and treatment with antiviral medications.