Antibiotic treatment of ceftriaxone-susceptible Serratia marcescens bacteremia: A multicenter, retrospective cohort study.

Background: Serratia marcescens has recently been categorized as low-risk for AmpC β-lactamase inducible production, but research on outcomes in Serratia bacteremia by antibiotic choice is limited.
Objectives: This study examined the clinical characteristics and outcomes of patients with ceftriaxone-susceptible Serratia bacteremia who received AmpC-directed β-lactam therapy vs. narrower spectrum therapies.
Materials and Methods: Records of hospitalized adults with at least one positive blood culture for Serratia , over an 8-year period, across seven hospitals in an integrated health care system, were reviewed.
Results: Of the 73 identified patients, 17 (23.3%) received carbapenem-based therapy. More than half of cases were community-acquired, with urological and intravenous drug use being the most common sources. While there was a trend toward lower mortality in carbapenem-treated patients (14.8 vs. 0%; p = 0.10), this was not statistically significant. The composite outcome of clinical failure was also not significant. However, compared to non-carbapenem-treated patients, carbapenem-treated patients had longer treatment duration (13 vs. 15 days; p = 0.02), prolonged hospital stays (5 vs. 11 days; p < 0.001), and higher infection-related readmission rates (17.6 vs. 3.6%; p = 0.04). A subset analysis of the 56 non-carbapenem treated patients found no significant difference in 30-day mortality or clinical failure between cefepime and non-cefepime-containing subgroups.
Conclusion: Our study found that cefepime- or carbapenem-based therapy may have limited clinical relevance in the treatment of Serratia bacteremia when the strains are initially susceptible to ceftriaxone, highlighting the importance of antibiotic stewardship to prevent emergence of multidrug resistant organisms.