Obesity as protective against, rather than a risk factor for, postoperative Clostridium difficile infection: A nationwide retrospective analysis of 1,426,807 surgical patients

BACKGROUND Recent studies suggest that obesity is a risk factor for Clostridium difficile infection, possibly due to disruptions in the intestinal microbiome composition. We hypothesized that body mass index (BMI) is associated with increased incidence of C. difficile infection in surgical patients. METHODS In this nationwide retrospective cohort study in 680 American College of Surgeons National Surgical Quality Improvement Program participating sites across the United States, the occurrence of C. difficile infection within 30 days postoperatively between different BMI groups was compared. All American College of Surgeons National Surgical Quality Improvement Program patients between 2015 and 2016 were classified as underweight, normal-weight, overweight, or obese class I-III if their BMI was less than 18.5, 18.5 to 25, 25 to 30, 30 to 35, 35 to 40 or greater than 40, respectively. RESULTS A total of 1,426,807 patients were included; median age was 58 years, 43.4% were male, and 82.9% were white. The postoperative incidence of C. difficile infection was 0.42% overall: 1.11%, 0.56%, 0.39%, 0.35%, 0.33% and 0.36% from the lowest to the highest BMI group, respectively (p < 0.001 for trend). In univariate then multivariable logistic regression analyses, adjusting for patient demographics (e.g., age, sex), comorbidities (e.g., diabetes, systemic sepsis, immunosuppression), preoperative laboratory values (e.g., albumin, white blood cell count), procedure complexity (work relative unit as a proxy) and procedure characteristics (e.g., emergency, type of surgery [general, vascular, other]), compared with patients with normal BMI, high BMI was inversely and incrementally correlated with the postoperative occurrence of C. difficile infection. The underweight were at increased risk (odds ratio, 1.15 [1.00-1.32]) while the class III obese were at the lowest risk (odds ratio, 0.73 [0.65-0.81]). CONCLUSION In this nationwide retrospective cohort study, obesity is independently and in a stepwise fashion associated with a decreased risk of postoperative C. difficile infection. Further studies are warranted to explore the potential and unexpected association. LEVEL OF EVIDENCE Prognostic/Epidemiologic, Level IV.