Performance Evaluation of QMAC-dRAST Using Consecutive Positive Clinical Blood Culture Samples

Abstract

Background: Bacteremia is life-threatening to patients, with a case fatality rate of 30–40%. The QMAC-dRAST system (QuantaMatrix, Republic of Korea), which is based on time-lapse imaging technology, can generate antimicrobial susceptibility testing (AST) results earlier than conventional equipment. Here, we evaluated the performance of QMAC-dRAST for positive blood culture samples. Methods: In total, 204 isolates were collected from positive blood cultures, with 104 Gram-positive cocci (GPC) and 100 Gram-negative rods (GNR), including Staphylococcus spp., Enterococcus spp., Enterobacteriaceae, Pseudomonas aeruginosa, and Acinetobacter spp. Before and after improvement of the AST algorithm, 67 GPC isolates and 72 GNR isolates were tested and their results were compared. In the final test, 37 GPC and 28 GNR were added, and the agreement rates between QMAC-dRAST and Vitek 2 were analyzed using 204 samples. To resolve discrepant AST results between two systems, broth microdilution tests were performed. Results: In the first and second tests with 67 GPC and 72 GNR, the categorical agreement (CA) between QMAC-dRAST and Vitek 2 was increased from 92.7% and 96.2% to 94.3% and 96.5% by updating the AST algorithm, respectively. For all 204 samples, the agreement rates were 94.5% and 95.4% for CA; 4.8% and 0.6% for very major errors; 2.5% and 2.0% for major errors; and 2.1% and 3.0% for minor errors. Conclusions: The QMAC-dRAST system has reliable performance and the advantage of faster AST reporting than conventional methods. This system will demonstrate more acceptable agreement rates with conventional AST systems in the future by improving AST algorithms.