Clinical characteristics and outcomes of patients with bacteraemia caused by non-carbapenemase-producing, carbapenem-resistant Enterobacterales.

OBJECTIVES: Carbapenem-resistant Enterobacterales (CRE) are classified as carbapenemase- and non-carbapenemase-producing (non-CP) CRE. The purpose of this study was to identify factors associated with meropenem non-susceptible non-CP CRE to help stratify treatment approaches and to report rates of treatment-emergent resistance among patients with non-CP CRE bacteraemia. METHODS: This was a retrospective, single-centre study of patients hospitalized between January 2015 and September 2025 with bacteraemia due to Enterobacterales resistant to ertapenem and confirmed to be non-CP. Ertapenem resistance was determined by broth microdilution susceptibility testing. Carbapenemase testing was performed by modified carbapenem-inactivation method, polymerase chain reaction or whole-genome sequencing. RESULTS: Among 60 patients who met the inclusion criteria, the median (IQR) age was 63 years (57-73), 33% (20/60) were female and 18% (11/60) were organ transplant recipients. Patients infected with meropenem non-susceptible non-CP CRE were more likely to have prior meropenem exposure [60% (10/15) versus 13% (8/45), P < 0.001] and have breakthrough bacteraemia [60% (9/15) versus 29% (13/45), P = 0.031]. Treatment-emergent resistance developed in 16% (4/24) and 0% (0/15) of patients treated with meropenem and ceftazidime-avibactam, respectively. CONCLUSIONS: These exploratory data provide new insights into clinical factors associated with meropenem non-susceptible non-CP CRE and support future investigations into the comparative-effectiveness of meropenem versus beta-lactam/beta-lactamase inhibitors for the treatment of meropenem-susceptible non-CP CRE.