Carbapenem-resistant Enterobacteriaceae (CRE) detection practices in California: What are we missing?

Abstract

Background

The Clinical and Laboratory Standards Institute (CLSI) revised carbapenem breakpoints for the Enterobacteriaceae in 2010. The number of hospitals that adopted revised CLSI breakpoints and the clinical impact of delayed adoption has not been previously explored.

Methods

We performed a cross-sectional, voluntary survey of microbiology laboratories that serve California acute care hospitals and long-term acute care hospitals (LTAC) to determine use of revised CLSI breakpoints. CRE clinical isolates from a single tertiary care hospital from 2013 to 2017 were examined. All isolates with an elevated minimum inhibitory concentration (MIC) (≥ 2 µg/mL) to imipenem or meropenem were tested for the presence of a carbapenemase gene by PCR.

Results

We received responses from 128 laboratories that serve 264/393 (67%) of hospitals and LTACs. Current CLSI carbapenem breakpoints for Enterobacteriaceae were used by 92/128 (72%) laboratories. Among laboratories using current breakpoints, time to implementation varied from 0 – 68 months (mean, 41 months, median, 55 months). Application of historical breakpoints to isolates in with a carbapenemase gene detected by PCR resulted in susceptibility rates of 8.9%, 18.6%, and 18.6% to ertapenem, imipenem, and meropenem, respectively. By current breakpoints, <1% of these isolates were susceptible to ertapenem or imipenem and 2.6% to meropenem.

Conclusion

Clinicians and epidemiologists should be aware that use of outdated MIC breakpoints for Enterobacteriaceae remains common and can result in reports of false susceptibility to carbapenems and missed identification of carbapenemase producers. This misclassification could have consequences for patient care and infection control efforts to address carbapenemase-producing Enterobacteriaceae.