Clinical sensitivity and specificity of the Check-Points Check-Direct ESBL Screen for BD MAX, a real-time PCR for direct ESBL detection from rectal swabs

Abstract

Objectives: To determine the diagnostic accuracy of the Check-Direct ESBL Screen for BD MAX (ESBL qPCR) and an ESBL culture method to identify ESBLs directly fromrectal swabs. Methods: Rectal swabs were obtained from clinical patients by performing cross-sectional (point)prevalence measurements in three regional hospitals. Rectal swabs were analysed by direct culture (ChromID ESBL agar) and with the ESBL qPCR. Suspected ESBL-producing isolates were confirmed with the combination disc method and analysed by WGS. Results: Out of 354 rectal swabs and 351 patients, 21 rectal swabs and 20 patients were positive for ESBLproducing isolates, resulting in a regional ESBL colonization prevalence of 5.7%. One rectal swab was false negative with the ESBL qPCR (blaTEM-12) and not covered by the ESBL qPCR. Eight ESBL qPCR-positive rectal swabs could not be confirmed by culture and were classified as false ESBL qPCR positive. The sensitivity and specificity of the ESBL qPCR were 95.2%(n=20) and 97.6%(n=323), respectively. When an optimal cycle threshold cut-off value of 37 was used, the ESBL qPCR displayed a sensitivity and specificity of 95.2% (n=20) and 98.8% (n=327), respectively (AUC=0.975, 95% CI=0.922-1). Conclusions: This ESBL qPCR offers rapid direct detection of the most prevalent ESBL types (blaCTX-M group and blaSHV group) from rectal swabs. The relatively high false-positive rate renders this test the most suitable as a screening test in high-prevalence regions or in an outbreak setting where a fast result is essential.