Development and clinical evaluation of a new multiplex PCR assay for a simultaneous diagnosis of tuberculous and nontuberculous mycobacteria

Background: The prevalence of non-tuberculous mycobacteria (NTM) has been increasing worldwide in both developed and developing countries. NTM infection is clinically indistinguishable from tuberculosis and therefore poses significant challenges in patient management, especially in patients chronically treated for pulmonary TB. In this study, we evaluated a new highly sensitive Multiplex MTB/NTM assay that can differentiate M. tuberculosis complex (MTBC) from all NTM, including the treatable and most common NTM, M. avium complex (MAC). Methods: We developed and optimized a new open- Multiplex MTB/NTM assay with two gene-targets for MTBC (IS6110/senX3-regX3) and two targets for MAC (IS1311/DT1) with samples spiked with stored strains and testing 20 replicates. Patients with presumptive TB and NTM were enrolled at the Respiratory Disease Department of The University Teaching Hospital of Point G, in Mali. Findings: In the development stage, the new assay showed a high analytic performance with 100% detections of MTBC and MAC at only 5 colony forming units (CFUs). Overall, without the treatment failure cases, the Multiplex assay and the Xpert showed a sensitivity, specificity, PPV and NPV of 813% [66.4-92.6], 96.6% [88.6-99.0], 92.5% [82.3-96.5] and 92.2% [82.7-96.5] and the Xpert had values of 96.7% [83.3-99.4], 80.0% [68.2-88.1], 70.7 [55.5-823] and 97.9% [89.3-99.6], respectively. The Multiplex assay successfully detected all (5/5) the MAC cases. Interpretation: Our new Multiplex assay demonstrates better specificity than Xpert for all group studied, in addition to detecting potential NTM cases. The assay could therefore complement the widely used Xpert assay and enhance discrimination of TB and NTM infections. (C) 2021 The Author(s). Published by Elsevier B.V.

Automated summary

This study evaluated a new Multiplex MTB/NTM assay that can differentiate between MTBC and NTM with high sensitivity and specificity. The assay showed 100% detection rate for MAC at 5 CFUs and demonstrated better specificity than Xpert, enhancing discrimination between TB and NTM infections.