Impact of a Rapid Change in Beta-lactam Resistance Epidemiology on the Management of Patients With Bloodstream Infections.

The impact of a shift in the epidemiology of ceftriaxone resistance among Escherichia coli and Klebsiella pneumoniae recovered from blood cultures was evaluated. 163 patients were included for analysis, 139 (85.3%) with bla CTX-M detected and 24 (14.7%) without bla CTX-M detected by molecular testing. All but 1 case in the no-CTX-M cohort occurred in 2024. Patients in the bla CTX-M detected cohort were started on optimal antimicrobial treatment significantly earlier than patients in the no bla CTX-M detected group (18.6 vs 59.2 hours, P < .001). Between 2022 and 2024, the rate of CTX-M negative ceftriaxone-resistant E. coli (n = 14) and K. pneumoniae (n = 10) increased from 3.2% to 5.6% to 20.3%, while at the same time the rate of ceftriaxone susceptibility decreased for both species. Whole genome sequencing identified AmpC genes (bla CMY-2, bla DHA-1, and bla FOX-5), TEM extended-spectrum beta-lactamases (ESBL) variants (bla TEM-190) and SHV ESBL variants (bla SHV-12 and bla SHV-7) as the likely cause of ceftriaxone resistance in these isolates. Despite this change, the negative predictive value for the test was 94% in 2024. Our data suggest continued reliance on molecular testing for de-escalation is appropriate for most patients, although rapid follow-up of final susceptibility results is warranted. In addition, institutions should be aware that epidemiology changes may occur and routinely monitor the incidence of ceftriaxone resistant but bla CTX-M-negative isolates.