Too Hot to Handle: Investigating Seasonal Variations in Surgical Site Infections after Colorectal Surgery.

Surgical site infections (SSIs) increase morbidity and cost following colorectal surgery. Seasonal variabilities in SSI were shown in orthopedic and neurological operations but not yet investigated in colorectal surgery. We studied the seasonal trends of SSI in colorectal operations and hypothesized that warmer weather increases the risk of SSI. This was a retrospective cohort study. Patients were identified from the National Surgical Quality Improvement Program and assigned to the warm (April to September) or cold cohort (October to March). All patients undergoing colorectal surgery between 2006 and 2021 without significant additional procedures were included. Our primary aim was to identify the difference in SSI rates between cohorts, whereas secondary aims included further characterization of the onset and type of SSI, as well as identifying the incidence of reoperation because of SSI. The final study population included 306,984 patients, with 155,137 (50.5%) in the cold cohort and 151,847 (49.5%) in the warm cohort. The warm cohort had higher odds of overall SSI (odds ratio [OR]: 1.04, 95% confidence interval [CI]: 1.02-1.07), with higher rates of superficial SSIs (OR: 1.08, 95% CI: 1.04-1.12) and comparable rates of deep incisional (OR: 1.02, 95% CI: 0.93-1.11) and organ space SSI (OR: 1.01, 95% CI: 0.97-1.05). SSIs occurred post-discharge more often in the warm cohort (57.1% vs. 55.9%, p = 0.048). Patients in the warm cohort also had higher odds of reoperation (OR: 1.39, 95% CI: 1.15-1.67). This study has limitations inherent in retrospective research and the use of a national-level database, such as missing data and differences in reporting standards from each participating center. Our study showed that patients undergoing colorectal surgery during warm weather months were at higher risk of superficial SSI and reoperation because of infection than those in colder weather.