Utility of Point-of-care Xpert Mycobacterium tuberculosis/XDR Assay in the Detection of Isoniazid and Second-line Anti-tubercular Drug Resistance at a Tertiary Care Hospital in India

Abstract Background: The emergence of drug-resistant tuberculosis (TB) poses a major diagnostic and therapeutic challenge. Conventional phenotypic drug susceptibility testing is time-consuming and hazardous, while molecular assays detect only rifampicin (RIF) resistance. The recently introduced Xpert Mycobacterium tuberculosis (MTB)/XDR assay can detect resistance to both first- and second-line anti-TB drugs in a single test. Objective: The objective of the study was to evaluate the performance of the Xpert MTB/XDR assay in detecting resistance to isoniazid and second-line anti-tubercular drugs among MTB complex (MTBC) positive samples detected by Xpert MTB/RIF Ultra. Materials and Methods: A prospective, cross-sectional study was conducted over 8 months, where one hundred MTBC-positive samples detected by Xpert MTB/RIF Ultra were tested using the Xpert MTB/XDR assay for the detection of resistance to isoniazid, ethionamide, fluoroquinolones and second-line injectable drugs (SLIDs). Results: Of the 100 samples, 89 (89%) were MTBC positive on Xpert MTB/XDR. Among these, resistance to isoniazid was seen in 20 (22.5%), fluoroquinolones in 17 (19.1%) and SLIDs in 2 (2.2%). Most trace category samples on Xpert MTB/RIF Ultra tested negative on Xpert MTB/XDR. Conclusion: The Xpert MTB/XDR assay enables the rapid detection of both first- and second-line drug resistance directly from the clinical samples and can guide optimal treatment decisions in both RIF-sensitive and RIF-resistant TB cases.