Evaluation of a commercial microarray as a confirmation test for the presence of extended-spectrum β-lactamases in isolates from the routine clinical setting.

Since the diagnostic characteristics of the Check-KPC ESBL microarray as a confirmation test on isolates obtained in a routine clinical setting have not been determined, we evaluated the microarray in a random selection of 346 clinical isolates with a positive ESBL screen test (MIC >1 mg/L for cefotaxime or ceftazidime or an ESBL alarm from the Phoenix or Vitek-2 expert system) collected from 31 clinical microbiology laboratories in the Netherlands in 2009. Using sequencing as the reference method the sensitivity of the microarray was 97% (237/245), the specificity 98% (97/99), the positive predictive value 99% (237/239) and the negative predictive value 92% (97/105).