AUTHORS: Brittany Shellhouse, Eric Shaw, Amy Taylor
BACKGROUND: National Healthcare Safety Network (NHSN) defines a surgical site infection (SSI) as an infection that was not present at time of surgery but occurred within 30 days post-operatively. Due to their significant effect on morbidity, hospital length of stay, and costs, national guidelines recommend initiation of most pre-operative antibiotics within 60 minutes of surgery. They also include specific guidance on the choice of agent to use with the various types of procedures, as well as dosing recommendations and re-dosing strategies. The purpose of this study was to examine if there is a correlation between timing of pre-operative antibiotics on the development of post-operative infections, and to examine other potential risk factors for the development of SSIs.
METHODS: This study was a retrospective, single-center, case-control study, which took place at a level-one trauma academic medical center in the United States. It included adults who received pre-operative antibiotics for colorectal and/or hysterectomy surgeries between January 1, 2023 through September 26, 2025. Patients were excluded if they had infections documented as present at time of surgery, or if they were pregnant or incarcerated at time of admission. The event group included patients with NHSN defined SSIs. The control group was matched 1:1 based on surgery type and consisted of patients who did not have a documented SSI. Patients were identified with assistance from the Infection Prevention Workgroup’s data collection of all surgical procedures.
The primary endpoint compared association of antibiotic timing with incidence of post-operative infection. Secondary outcomes included the comparative risk of antibiotic(s) selection, surgery type, emergent versus scheduled surgery, administration of repeat dosing during surgery, continuation of post-operative prophylactic antibiotics, and personnel present at surgery.
RESULTS: This study included 96 total patients matched 1:1 with events versus controls within each group for hysterectomy, colorectal surgeries, and colorectal plus hysterectomy surgeries (40 patients, 52 patients, and 4 patients respectively). For the primary outcome, the median time of antibiotic start and completion prior to surgery was 23 minutes and 15 minutes for the control group and 15.5 minutes and 9 minutes for the event group. While all antibiotics selected for hysterectomy procedures were correct per guidelines, there was a numerical difference in optimized dosing for the control versus the event group (85% vs 65% respectively). Similarly, all patients were in compliance with repeat dosing per guidelines, but zero patients in the control group received antibiotics post-operatively compared with 5% of patients in the event group.
Appropriate antibiotic selection for colorectal procedures was 65% versus 54% for the control versus the event group; optimized dosing per guidelines was 67% versus 77% for controls versus event group. There was a numerical difference for control versus event group in required repeat per protocol (91% vs 70%), bowel prep administration (58% vs 19%), and use of post-operative antibiotics (27% vs 58%). For combination colorectal surgery plus hysterectomy, there was a numerical difference in incidence of emergent surgeries for control versus event group (0% vs. 50%). However, this difference was inverse for antibiotic selection with 50% versus 100% compliance for control versus event group.
CONCLUSION: There was a numerical difference in perioperative timing of antibiotics, but no definitive trend in additional factors for increasing risk of SSI development. Limitations to this study were small sample size and inclusion of only two surgery types. Further research across various surgery types may be beneficial in distinguishing perioperative antibiotic timing.
