890 - Incidence and Microbiology of Surgical Site Infection (SSI) after Breast Surgery

Background: Surgical site infection (SSI) after breast surgery is much more common than expected after a clean surgical procedure. Although 
breast SSIs are primarily Gram-positive; recent literature shows an increase in Gram-negative infections. We assessed the risk factors and microbiology of SSI following breast surgery at our institution.

Methods: We conducted a historical cohort study of all ( ³ 18 y) females who had surgery from 1/1/2014-3/31/2019 and subsequent SSI within 90 days of the procedure. Two controls, matched for surgery type, were selected per case. Data were collected on demographic and clinical characteristics, surgery type, microbiology and antibiotics. Data were analyzed using the χ² test, Student’s t-test and multivariable logistic regression with a forward likelihood ratio algorithm.

Results: After excluding patients with limited data, we reviewed 284 charts: 95 of 132 cases and 189 controls.  The 90-day incidence of SSI was 3.5 % (132/3755). Cases were younger than controls: 53.9 ± 12.4 years vs. 58.3± 13.7 years, respectively, p=0.02. Controls had more comorbidities: 1.8 ± 1.3 vs. 1.4 ± 0.7,respectively, p=0.001. Tissue expanders were placed in 65 (70%) cases versus 11 (5.8%) controls (p < 0.0001).  After controlling for age, BMI, comorbidities and post-operative antibiotics, only tissue expanders were associated with infection (OR=35.1, p< 0.0001, 95% CI: 16.6, 74.0).
Microbiological data were available for 84 cases.  Gram-positive organisms accounted for 45 (53.6%) infections and Gram-negative organisms accounted for 39 (46.4%) infections. Over 72% of African Americans (p= 0.014), 76.5% of patients with diabetes (p=0.005) and 57.1 % with tissue expanders (p= 0.02) had Gram-negative infections. The table shows the multivariable predictors of Gram-negative infection. Tissue expander removal was required in 61.5% of patients with Gram-negative infections compared to 39% with Gram-positive infections.Predictors of Gram-negative SSI after breast surgery


Conclusion: Patients with tissue expanders had a higher incidence of SSI after breast surgery; removal was often required in Gram-negative infections. Diabetes and post-operative antibiotics were significant predictors of Gram-negative infection. Knowledge of local epidemiology is a key factor in deciding empiric therapy for SSI.