(184) Histologic Chorioamnionitis as a Marker for Surgical Site Infection

Objective: Clinical chorioamnionitis is a known risk factor for c-section surgical site infection (SSI). As histologic chorioamnionitis (HCA) is a marker for intraamniotic infection, we hypothesized that the frequency of HCA would be increased in SSI.

Study Design: This was a case-control study of singleton pregnancies having had c-sections from 2002-2022, in which the placenta was submitted to pathology. Subjects were identified via electronic information management system query. Univariate comparisons of SSI and non-SSI groups were made using Student's t-test and chi-square test. We calculated that 189 patients (126 controls and 63 cases) would be needed to detect a two-fold increased rate of HCA, using a two-sided test, with 80% power and significance level of 0.05. Logistic regression analysis tested whether or not HCA was an independent predictor of SSI.

Results: The estimated incidence of SSI was 6.95%. 63 cases of SSI were compared to 127 randomly selected controls (see Figure); about 32% of subjects labored. Presence of HCA was higher in cases (20.6%) than in controls (9.4%), (OR 2.49, 95% CI [1.06, 5.84]). After adjusting for the independent variables of labor, ruptured membranes, pre-pregnancy BMI, nonreassuring fetal heart status, and preoperative vaginal preparation HCA was no longer significantly associated with SSI. Independent positive predictors for SSI included increasing BMI and c-section for non-reassuring fetal status, while having had a vaginal prep reduced the odds of SSI (see Table).

Conclusion: HCA was increased in cases but was not an independent predictor of SSI. The strength of this study was using a standardized definition for SSI and individual patient chart review. The study was limited by the sample size, and that the majority of cases didn't labor. As intraamniotic infection and HCA are relatively rare in nonlaboring patients, future studies should include only SSI in cesarean section after labor. If HCA were found to be an independent risk factor for SSI, this could be a group to target for further studies on the efficacy of postpartum antibiotic prophylaxis in reducing SSI.