(563) Outcomes Associated With Anti-Pseudomonal Beta-Lactams for Treatment of MSSA Bacteremia

Introduction: Staphylococcus aureus bacteremia is a serious bacterial infection associated with increased mortality and prolonged hospital length of stay. The purpose of this study was to determine if differences in outcomes exist in patients treated with cefazolin or oxacillin vs. anti-pseudomonal beta-lactams (APBLs) for methicillin-susceptible Staphylococcus aureus (MSSA) bacteremia.

Methods: This was a single-center, retrospective cohort study performed at an academic medical center. The study included adult and pediatric patients hospitalized between June 1, 2016 and June 30, 2023 with at least one positive blood culture for MSSA who received at least 14 consecutive days of inpatient therapy with cefazolin, oxacillin, cefepime, piperacillin-tazobactam, or meropenem. Patients who received APBLs were compared to those who received cefazolin/oxacillin. The primary outcome was composite clinical failure (defined as 30-day mortality and/or bacteremia recurrence within 30 days). Secondary outcomes included 60-day mortality, intensive care unit (ICU) and hospital length of stay, 30-day readmission, time to blood culture clearance, time to mortality, and incidence of adverse events (i.e., Clostridioides difficile infection, hepatotoxicity, and acute kidney injury).

Results: One-hundred patients were included in the study, with 50 patients in each group. The most common source of MSSA bacteremia was catheter-related infection (28% total) and twice as many patients met criteria for complicated MSSA bacteremia in the cefazolin/oxacillin group (80% vs. 40%, P < 0.0001). Three patients (6%) in the APBL group met the composite primary outcome compared to 1 (2%) in the cefazolin/oxacillin group (P = 0.62). There were no significant differences in secondary outcomes.

Conclusions: No differences were found in mortality and bacteremia recurrence rates among patients with MSSA bacteremia treated with APBLs compared to cefazolin and/or oxacillin. Larger studies should be performed to confirm these findings.