Evaluation of Nordmann, Dortet, and Poirel test for the identification of extended spectrum betalactamase production among urinary isolates of Escherichia coli

CONTEXT: Current phenotypic techniques for extended spectrum beta lactamase (ESBL) detection can be interpreted after 24 h of incubation only, resulting in a delay in initiating therapy. Nordmann, Dortet, and Poirel (NDP) in 2012 proposed a novel test named ESBL NDP to overcome this limitation. AIMS: This study aimed to evaluate the ESBL NDP test for the identification of ESBL among Escherichia coli isolates against the Clinical Laboratory Standards Institute-recommended phenotypic confirmatory method. SETTINGS AND DESIGN: This cross-sectional study was conducted over a period of 3 months on a sample size of 100. SUBJECTS AND METHODS: One hundred nonduplicate clinically significant E. coli urinary isolates positive by initial screening test for ESBL were subjected to the ESBL NDP test and phenotypic confirmatory test. The NDP test was evaluated by determining the sensitivity, specificity, kappa value, and confidence interval (CI) for kappa. RESULTS: The phenotypic confirmatory test and the ESBL NDP test were positive in 82% and 63% of the isolates, respectively. ESBL NDP test had a sensitivity and specificity of 76% and 100%, positive and negative predictive values of 100% and 48%, respectively, kappa value of 0.54 (moderate agreement), and 95% CI for kappa of 0.43–0.66. The time to positivity was 1 h in 93.6% of the isolates. CONCLUSION: The NDP test showed a good specificity, with time to positivity of 1 h. The low sensitivity could be due to the difference in the phenotypic type of ESBL producer and technical reasons.