Surgical site infection is one of the most common complications of gynecologic cancer surgery. Current guidelines recommend the administration of cefazolin preoperatively to reduce surgical site infection rates for patients undergoing clean-contaminated surgeries such as hysterectomy.

To evaluate the impact of a quality improvement project adding metronidazole to cefazolin for antibiotic prophylaxis on surgical site infection rate for women undergoing gynecologic surgery at a comprehensive cancer center.

This retrospective, single-center cohort study included patients who underwent surgery in the gynecologic oncology department from May 2017 to June 2023. Patients with penicillin allergies and those undergoing concomitant bowel resections and/or joint cases were excluded. The preintervention group patients had surgery from May 2017 to April 2022, and the postintervention group patients had surgery from April 2022 to June 2023. The primary outcome was a 30-day surgical site infection rate. Sensitivity analyses were performed to compare surgical site infection rates on the basis of actual antibiotics received and for those who had a hysterectomy. Factors independently associated with surgical site infection were identified using a multivariable logistic regression model adjusting for confounding variables.

Of 3343 patients, 2572 (76.9%) and 771 (23.1%) were in the pre-post intervention groups, respectively. Most patients (74.7%) had a hysterectomy performed. Thirty-four percent of cases were for nononcologic (benign) indications. Preintervention patients were more likely to receive appropriate preoperative antibiotics (95.6% vs 90.7%; P<.001). The overall surgical site infection rate before the intervention was 4.7% compared with 2.6% after (P=.010). The surgical site infection rate for all patients who underwent hysterectomy was 4.9% (preintervention) vs 2.8% (postintervention) (P=.036); a similar trend was seen for benign cases (4.4% vs 2.4%; P=.159). On multivariable analysis, the odds ratio for surgical site infection was 0.49 (95% confidence interval, 0.38–0.63) for the postintervention compared with the preintervention group (P<.001). In a sensitivity analysis (n=3087), the surgical site infection rate was 4.5% for those who received cefazolin alone compared with 2.3% for those who received cefazolin plus metronidazole, with significantly decreased odds of surgical site infection for the cefazolin plus metronidazole group (adjusted odds ratio, 0.40 [95% confidence interval, 0.30–0.53]; P<.001). Among only those who had a hysterectomy performed, the odds of surgical site infection were significantly reduced for those in the postintervention group (adjusted odds ratio, 0.63 [95% confidence interval, 0.47–0.86]; P=.003).

The addition of metronidazole to cefazolin before gynecologic surgery decreased the surgical site infection rate by half, even after accounting for other known predictors of surgical site infection and differences in practice patterns over time. Providers should consider this combination regimen in women undergoing gynecologic surgery, especially for cases involving hysterectomy.