Abstract and Introduction
Background Obesity was recognized as in independent risk factor for influenza during the 2009 H1N1 influenza pandemic.
Objectives We evaluated the association between body mass index (BMI) and influenza-like illness (ILI) during two non-pandemic influenza seasons (2003–2004 and 2004–2005) and during the spring and fall waves of the 2009 H1N1 pandemic.
Methods Adults with severe (inpatient) and mild (outpatient) ILI were compared to those without ILI using a case-cohort design. The study was nested among those insured by a single health insurance company, receiving care from a large multispecialty practice. Data were collected from insurance claims and the electronic health record. The primary exposure was obesity (BMI ≥ 30·0 kg/m2).
Results Across three seasons, the crude and adjusted ORs for obesity and severe ILI were 1·65 (95% CI 1·31, 2·08) and 1·23 (95% CI 0·97, 1·57), respectively. An association was observed for those aged 20–59 years (adjusted OR 1·92, 95% CI 1·26, 2·90), but not for those 60 and older (adjusted OR 1·08, 95% CI 0·80, 1·46). The adjusted ORs for obesity and severe ILI in 2003–2004, 2004–2005, and during H1N1 were 1·14 (95% CI 0·80, 1·64), 1·24 (95% CI 0·86, 1·79), and 1·76 (95% CI 0·91, 3·42), respectively. Among those with a Charlson Comorbidity Index score of zero, the adjusted ORs for 2003–2004, 2004–2005, and H1N1 were 1·60 (95% CI 0·93, 2·76), 1·43 (95% CI 0·80, 2·56), and 1·90 (95% CI 0·68, 5·27), respectively.
Conclusions Our results suggest a small to moderate association between obesity and hospitalized ILI among adults.
Early investigations of 2009 pandemic influenza A H1N1 (2009 H1N1) noted that severity of illness was associated with obesity.[1–6] Subsequent analyses suggested an association of obesity with both hospitalization and death from 2009 H1N1.[7–9] Before the 2009 H1N1 pandemic, however, obesity was not recognized as an independent risk factor for influenza in general and severe influenza in particular.
Two groups have recently examined the association between body mass index (BMI) and influenza during non-pandemic influenza seasons. Coleman and co-authors conducted a case–control study of outpatient, laboratory-confirmed influenza during two typical flu seasons (2007–2008 and 2008–2009) and the 2009 pandemic season. They found no differences in mean body mass index (BMI) between cases and controls in each season. They interpreted their multivariate model as indicating no evidence of an association between obesity and influenza, although there was evidence – albeit not statistically significant – of increased odds of medically attended influenza among at least the highest category of BMI during the 2009 pandemic. Another group examined the association between obesity and respiratory hospitalizations in Ontario, Canada. These authors combined hospitalization claims data with self-reported BMI from 12 influenza seasons and found an association between obesity and hospitalized respiratory conditions among patients with and without recognized risk factors for severe influenza complications (i.e., chronic health conditions such as heart and respiratory disease).
Given these conflicting data, we examined the association between obesity and influenza-like illness (ILI) incidence and severity among adults during two non-pandemic influenza seasons (2003–2004 and 2004–2005) and during the spring and fall waves of the 2009 H1N1 pandemic. We hypothesized that obesity would be associated with increased risk for hospitalized ILI during non-pandemic influenza seasons as well as during pandemic H1N1.
Influenza Resp Viruses. 2014;8(1):25-32. © 2014 Blackwell Publishing