Adaptation and performance evaluation of the French society of microbiology algorithm for detection of carbapenemase-producing enterobacterales using VITEK2 antibiotic susceptibility testing system.

Carbapenemase-producing Enterobacterales (CPE) must be closely tracked for their involvement in difficult-to-treat infections and outbreaks. Therefore, the screening process for detecting these strains must be optimal. This study aimed to evaluate the performance of an adapted version of the French CA-SFM algorithm for detecting CPE, using the VITEK2 automated system, and compare it to the standard VITEK2 CPE detection algorithm. A retrospective monocentric study was conducted from 2021 to 2023 at the Hospices Civils de Lyon microbiology platform. Antibiotic susceptibility testing results from 1 401 rectal screening swabs and 4 949 blood cultures were collected. CPE status was determined using biochemical and molecular confirmation tests, with whole genome sequencing for subtyping. The adapted CA-SFM algorithm evaluated susceptibility to ceftazidime-avibactam, temocillin, and carbapenems, while the standard VITEK2 algorithm relied solely on carbapenem MICs. Sensitivities, specificities, positive and negative predictive values (PPV, NPV) were statistically compared using Fisher's exact test. The adapted CA-SFM algorithm demonstrated 100% sensitivity and NPV for both sample types, significantly outperforming the standard VITEK2 algorithm (97.1% sensitivity, p < 0.0001). In rectal swabs, the standard VITEK2 algorithm missed 38 CPE strains, while one CPE strain was undetected in blood cultures. Most missed detections involved OXA-48-like (20 OXA-48, 12 OXA-181) and 6 VIM-1 producers. The adapted CA-SFM algorithm offers enhanced detection of CPE, particularly for OXA-48-like strains with weak carbapenem hydrolysis, which are often missed by carbapenem MIC-based methods alone. Given the clinical risks of under-detection and transmission, implementing the adapted CA-SFM algorithm strategy could strengthen infection control and antimicrobial stewardship efforts.