2026 Eastern States Conference

Authors: Alexander J. Ruehman, PharmD; Mandee Booth, PharmD, BCIDP; Alexander Cain, PharmD BCIDP 
Learning Objective: Audience members will be able to describe appropriate treatment regimens for low-risk AmpC infections
Self-Assessment Question: Which of the following is the most appropriate treatment option for susceptible Morganella morganii blood stream infection? A. Ceftriaxone B. Cefepime C. Cefazolin D. More data needed
Background/Objective: The Infectious Diseases Society of America provides guidance that ceftriaxone or piperacillin/tazobactam may be used for susceptible, low-risk AmpC isolates; however, optimal treatment remains controversial.
Methods: This single-center retrospective study included adults with blood cultures growing S. marcescens or M. morganii from January 1, 2020 to December 31, 2024. Patients were excluded if isolates were resistant to ceftriaxone (CRO) or piperacillin/tazobactam (TZP) or if definitive therapy did not include CRO, TZP, cefepime, or a carbapenem. Data collected included demographics, level of care, infection source, and treatment duration. The primary outcome was clinical treatment failure, defined as death during therapy, 30-day all-cause mortality, escalation from CRO or TZP during definitive therapy, or infection recurrence within 30 days. Secondary outcomes included Clostridioides difficile infection within 90 days of antibiotic completion and infection-related readmission within 30 days. Descriptive statistics summarized variables; categorical data were analyzed using chi-square or Fisher’s exact tests, and multivariable analysis identified risk factors for treatment failure.
Results: A total of 103 patients were included in the study with 47 in the CRO/TZP group and 56 in the FEP/CBP group. Serratia marcescens comprised most infections (90%). Median duration of definitive and total treatment did not differ between groups. Patients in the FEP/CBP group had a longer length of stay (34.5 vs 24 days, p=0.013) and hospital-acquired infection (91.1% vs 66%, p=0.0016). Incidence of treatment failure was similar between groups (27.7% vs 25%, p=0.76) and there was no significant difference in secondary outcomes. No baseline characteristic, including age, severity of illness, immunocompromised status, or source of infection, were significantly associated with an increased risk of treatment failure.  
Conclusion: Definitive therapy with CRO/TZP was not associated with higher risk of clinical treatment failure when compared to FEP/CBP, suggesting that definitive antibiotic selection based on sensitivity results does not increase risk of treatment failure. The findings of this study are largely limited to S. marcescens infections treated with 7-14 days of therapy, and future studies are needed for other low-risk AmpC infections and those requiring treatment durations exceeding 14 days.