Surgical site infections (SSIs), defined as infections occurring within 30 days of surgery at the incision or operative organ space, remain a significant source of postoperative morbidity. Although the adoption of minimally invasive techniques has reduced SSI rates to approximately 1–2.5%, the incidence remains substantially higher in open gynecologic oncology procedures, reported as high as 5–35% in some settings. SSIs contribute to increased healthcare utilization, including readmissions and reinterventions, and are associated with worsened patient outcomes, making them a key target for quality improvement initiatives. While perioperative prophylaxis with cefazolin remains the standard of care for hysterectomy per American College of Obstetricians and Gynecologists recommendations, this approach may not adequately cover anaerobic vaginal flora inherent to these procedures. Emerging evidence suggests that the addition of metronidazole to cefazolin may further reduce SSI rates, in particular hysterectomies for malignancy. This study is a quality improvement initiative to evaluate if the combination of cefazolin and metronidazole decreases the rate of surgical site infections and inpatient readmissions in hysterectomies at a single institution.

This is a retrospective cohort study conducted at University of Oklahoma Health Sciences Center, including patients treated from January 2023 through December 2025. We included female patients ≥18 years of age who underwent hysterectomy requiring perioperative antibiotic prophylaxis. Metronidazole was formally implemented as a standard Patients were excluded if their procedure did not warrant standard antibiotic prophylaxis, documented allergy to study antibiotics, preexisting infection, or did not receive standard prophylaxis. Additional exclusions included concomitant bowel resection, unplanned multi-team surgical cases, emergent procedures, and unplanned conversion from minimally invasive to open surgery. Patients were identified through the electronic medical record, and data was abstracted via chart review. Collected variables included demographics, clinical characteristics, and surgical variables. Postoperative outcomes included 30-day surgical site infections, type of infection, and need for intervention. De-identified data were analyzed following completion of data collection. Variables of interest were summarized and evaluated for association with surgical site infection outcomes.

A total of 799 patients were identified in the study period. After applying exclusion criteria, there were 242 patients in the pre-intervention group (7/1/2023-12/31/2023) and 393 patients in the post-intervention group (7/1/2025-12/31/2025). The median age was 51 years in pre-intervention and 48 years in the post-intervention group. In both the pre- and post-treatment groups, most cases were laparoscopic (86% in both). There was a statistically significant decrease in the rate of infections between the pre- and post-intervention groups (3.7% vs. 0.8%, p = 0.013). Abdominal hysterectomy is associated with about 4.3 times higher risk of SSI compared to minimally invasive approaches. On multivariable analysis, the post-intervention period and minimally invasive surgery remained associated with lower odds of SSI. Type 2 diabetes, tobacco use, BMI >30, EBL >1500mL, operative time >240 minutes, and cancer diagnosis were not associated with increased odds of SSI on multivariable analysis. 97.3% of patients received the correct perioperative antibiotic prophylaxis in the post-intervention group.

The addition of metronidazole to preoperative antibiotic prophylaxis resulted in a statistically significant decrease in postoperative surgical site infections.