Diagnostic characteristics of the Rapid ESBL NP® test and ResistanceFinder 2SMART multiplex PCR for the detection of ESBL directly on urine samples

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PURPOSE: To determine the diagnostic characteristics of the phenotypic Rapid ESBL NP® test and a prototype version of the molecular ResistanceFinder 2SMART multiplex PCR for the rapid detection of ESBL in patients with urinary tract infections. METHODS: The Rapid ESBL NP® test and the ResistanceFinder 2SMART multiplex PCR were performed on direct urine samples (enterobacterales, ≥105 CFU/ml and ≥ 3 plusses of leukocytes in Gram stain) collected at Rijnstate and Radboudumc and compared to conventional urine cultures. The sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) were calculated with 95% confidence intervals. RESULTS: In total, 218 urine samples were collected, of which 66 contained ESBL-producing bacteria, 102 contained Gram-negative bacteria without ESBL production and 50 contained no clinically significant growth. The Rapid ESBL NP® test gave 16 (7.3%) non-interpretable results. After excluding the non-interpretable results, the test had a sensitivity, specificity, PPV and NPV of 96.8% (89.0-99.6), 100% (97.4–100), 100% (94.1–100) and 98.6% (94.7–99.6), respectively. Using detection of CTX-M and VEB genes as positive, the ResistanceFinder 2SMART multiplex PCR had a sensitivity, specificity, PPV and NPV of 95.5% (87.3–99.1), 94.1% (89.1–97.3), 87.5% (78.8–93.0) and 98.0% (94.0-99.3), respectively. CONCLUSION: The NPVs for both tests were high. However, the lower PPV of the ResistanceFinder2 SMART multiplex PCR could lead to increased overuse of carbapenems when implemented into clinical practice. The Rapid ESBL NP® test could be a suitable screening tool for ESBL-producing bacteria in clinical urine samples, ensuring more accurate prescription of antibiotics, though prospective validation is necessary first.

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