2788. Cefepime or Carbapenem Definitive Therapy Versus Other Antibiotics for Blood Stream Infections Caused by Non-ESBL-Producing Serratia Marcescens: A Multicenter Retrospective Cohort Study

BACKGROUND: Serratia Marcescens causes serious infections. Carbapenems were preferred due to fear of inducible AmpC resistance. IDSA guidance now recommends ceftriaxone, and in high-burden cases, cefepime. Evidence on Serratia bacteremia treatment is limited. This study compares outcomes of cefepime or carbapenem (CPCT) vs. non-cefepime non-carbapanem containing definitive therapy (NCPCT) in non-ESBL Serratia bacteremia. METHODS: We retrospectively reviewed adults (≥18 years) with Serratia Marcescens bacteremia hospitalized in seven Massachusetts acute care hospitals (2015 - 2022) (Figure 1). Demographics, clinical course characteristics, and antibiotic therapy choices were obtained. Primary outcome was 30-day mortality, and secondary composite outcome was antimicrobial failure (Definitions in Table 1 and 2). Chi Square and Mann-Whitney U tests were computed using SPSS statistical package. [Figure: see text] RESULTS: 69 out of 128 patients were included in the study. The mean age was 59.23 and 27.53% had IVDU disorder. 21.9 % of patients received CPCT while 78.1% were treated with NCPCT. Notably, more patients in the CPCT group received antibiotics in preceding 3 months, and had more ventilator associated pneumonia (VAP). Other baseline characteristics, bacteremia sources and severity of infection were similar between both groups (Table 1). CPCT patients had longer definitive therapy and more prolonged hospital stay, while more patients in the NCPCT group were switched to oral therapy (Table 2). Neither 30-day mortality rate (8.7% NCPCT vs. 5% CPCT, P= 0.602) nor antimicrobial failure rate (12.5 % NCPCT vs. 23.8% CPCT, P=0.238) was significantly different. [Figure: see text] [Figure: see text] CONCLUSION: Our study found no significant difference in 30-day mortality or antimicrobial failure between CPCT and NCPCT groups. Furthermore, longer hospital stay was observed in CPCT patients, possibly due to cefepime and meropenem’s less suitability for outpatient antimicrobial therapy (OPAT). Our study is limited by its small size and the overlap in definitive antibiotic therapy. Our findings suggest narrower Beta-lactam therapy may be appropriate which may help early hospital discharge and less days of broad spectrum therapy. Prospective studies are needed to confirm these conclusions and contribute to safe antimicrobial stewardship. DISCLOSURES: All Authors: No reported disclosures