Body Mass Index and 90-Day Mortality Among 35,406 Danish Patients Hospitalized for Infection

To examine the association between body mass index (BMI) and mortality after hospitalization for infection because obesity is associated with increased energy reserves that may protect against death from severe infections.

Of 76,044 patients admitted with a primary infection diagnosis from January 1, 2011, to September 30, 2015, in Central Denmark, we examined a subgroup of 35,406 patients with a known BMI. We compared the 90-day death risk among patients with underweight, overweight, or obesity with a reference cohort of normal-weight patients. We also examined the impact of comorbid conditions, including cancer, tobacco smoking, and recent weight changes, on the associations and adjusted for other potential confounding factors.

The 90-day mortality after hospital admission was 9.8% (3479 of 35,406) for any infection, 10.5% (466 of 4425) for urinary tract infection, 17.3% (1536 of 8855) for pneumonia, 24.9% (986 of 3964) for sepsis, and 6.2% (114 of 1831) for skin infection. The 90-day adjusted hazard ratio (aHR) for death was substantially increased in patients with underweight (aHR, 1.75; 95% CI, 1.58 to 1.94) compared with normal-weight patients. In contrast, mortality aHRs were decreased in patients with overweight (aHR, 0.64; 95% CI; 0.58 to 0.69) and obesity (aHR, 0.55; 95% CI; 0.49 to 0.62). Mortality reductions with overweight and obesity were consistent for all major infection types and remained robust independent of recent weight changes, smoking status, or comorbid conditions. Mortality was highest in patients without an apparent reason for their underweight (smoking/known disease), suggesting a role of undiagnosed comorbid conditions.

We found evidence that higher BMI (overweight and obesity) is associated with improved survival following acute hospitalization for infection, whereas underweight increases the risk for death.