Metronidazole and cefazolin versus cefazolin alone for surgical site infection prophylaxis in gynecologic surgery at a comprehensive cancer center

Background Surgical site infection (SSI) is one of the most common complications of gynecologic cancer surgery. Current guidelines recommend the administration of cefazolin pre-operatively to reduce SSI rates for patients undergoing clean-contaminated surgeries such as hysterectomy. Objective To evaluate the impact of a quality improvement project adding metronidazole to cefazolin for antibiotic prophylaxis on SSI rate for women undergoing gynecologic surgery at a comprehensive cancer center. Study Design This retrospective, single-center, cohort study included patients who underwent surgery in the Gynecologic Oncology department from 5/2017 to 6/2023. Patients with penicillin allergies and those undergoing concomitant bowel resection(s) and/or joint cases were excluded. The pre-intervention group patients had surgery from 5/2017 to 4/2022, and the post-intervention group patients had surgery from 4/2022 to 6/2023. The primary outcome was 30-day SSI rate. Sensitivity analyses were performed to compare SSI rates based on actual antibiotic(s) received and for those who had a hysterectomy. Factors independently associated with SSI were identified using a multivariable logistic regression model adjusting for confounding variables. Results Of 3343 patients, 2572 (76.9%) and 771 (23.1%) were in the pre- and post-intervention groups, respectively. Most patients (74.7%) had a hysterectomy performed. Thirty four percent of cases were for non-oncologic (benign) indications. Pre-intervention patients were more likely to receive appropriate pre-operative antibiotics (95.6% vs 90.7%; p<0.001). The overall SSI rate prior to the intervention was 4.7% compared to 2.6% after the intervention (p=0.010). The SSI rate for all patients who underwent hysterectomy was 4.9% (pre-intervention) vs. 2.8% (post-intervention) (p=0.036); a similar trend was seen for benign cases (4.4% vs 2.4%; p=0.159). On multivariable analysis, the odds ratio for SSI was 0.49 (95% CI 0.38-0.63) for the post- compared to pre-intervention group (p<0.001). In a sensitivity analysis (n=3087), SSI rate was 4.5% for those who received cefazolin alone compared to 2.3% for those who received cefazolin plus metronidazole, with significant decreased odds of SSI for the cefazolin plus metronidazole group (adjusted OR 0.40, 95% CI 0.30-0.53; p<0.001). Among only those who had a hysterectomy performed, the odds of SSI was significantly reduced for those in the post-intervention group (adjusted OR 0.63, 95% CI 0.47-0.86; p=0.003). Conclusion The addition of metronidazole to cefazolin before gynecologic surgery decreased the SSI rate by half, even after accounting for other known predictors of SSI and differences in practice patterns over time. Providers should consider this combination regimen in women undergoing gynecologic surgery, especially for cases involving hysterectomy.