Evaluation of Empiric β-Lactam Susceptibility Prediction among Enterobacteriaceae by Molecular β-Lactamase Gene Testing

was evaluated, using incidence rates of resistance mechanisms to third-generation cephalosporins, aztreonam, and piperacillin-tazobactam seen across U.S. census regions. Overall, the presence of CTX-M, KPC, and/or NDM genes was 81% (range, 57 to 87%) sensitive for the prediction of ceftriaxone, ceftazidime, and aztreonam resistance and 73% (range, 25 to 90%) sensitive for the detection of piperacillin-tazobactam resistance. The sensitivity of KPC or NDM to predict imipenem or meropenem resistance was 94.3% overall, and for meropenem ranged from 70 to 100% across U.S. census regions. Institutions that use genotypic RDTs to inform therapeutic de-escalation decisions should be aware of the incidence-base performance across U.S. geographies and in different patient populations, where resistance rates may vary.