Association Between Body Mass Index and Mortality in Patients With Gram-Negative Bloodstream Infections

Abstract

Background Obesity is an established risk factor for many infections. Emerging data demonstrate that increased body mass index (BMI) may paradoxically protect against mortality in several disease processes. The interaction between BMI and mortality in gram-negative bloodstream infections (GN-BSIs) remains unclear. Aim This retrospective cohort study examines the impact of BMI on mortality in patients with GN-BSI. Materials and Methods Hospitalized adults with first episodes of GN-BSI from 2010 to 2015 were identified. Patients were grouped by BMI in kilograms per meter squared as normal weight (18.5–24.9; reference), overweight (25.0–29.9), obese (30.0–39.9), and morbidly obese (≥40). Multivariate Cox proportional hazards regression was used to examine risk factors for 28-day mortality after GN-BSI. Results Among 1069 unique patients with GN-BSI, 352 (33%) were normal weight, 319 (30%) were overweight, 303 (28%) were obese, and 95 (9%) were morbidly obese. Overall, mean age was 63 years, and 54% were women. Crude 28-day mortality was higher in the normal-weight group (21.5%) than in the overweight (11.7%), obese (11.8%), and morbidly obese groups (8.7%; P = 0.003). After adjustments for age, chronic comorbidities, acute severity of illness, and antimicrobial therapy in a multivariate model, overweight BMI remained independently associated with reduced mortality (adjusted hazards ratio [aHR], 0.53; 95% confidence intervals [CI], 0.31–0.88; P = 0.01). There was no significant reduction in mortality in obese (aHR, 0.72; 95% CI, 0.43–1.15; P = 0.17) and morbidly obese patients (aHR, 0.71; 95% CI, 0.27–1.56; P = 0.41). Conclusions Compared with normal BMI, overweight patients had improved survival after GN-BSI. However, this potential protective effect was lost in obese and morbidly obese patients.