Performance evaluation of the Xpert MTB/XDR test for the detection of drug resistance to Mycobacterium tuberculosis among people diagnosed with tuberculosis in South Africa

Abstract

Drug-resistant tuberculosis (TB) poses a significant public health concern in South Africa due to its complexity in diagnosis, treatment, and management. This study assessed the diagnostic performance of the Xpert MTB/XDR test for detecting drug resistance in patients with TB by using archived sputum sediments. This study analyzed 322 samples collected from patients diagnosed with TB between 2016 and 2019 across South Africa, previously characterized by phenotypic and genotypic methods. The Xpert MTB/XDR test was evaluated for its ability to detect resistance to isoniazid (INH), ethionamide (ETH), fluoroquinolones (FLQ), and second-line injectable drugs (SLIDs) compared with phenotypic drug susceptibility testing (pDST) and whole-genome sequencing (WGS). Culture, Xpert MTB/RIF Ultra, and Xpert MTB/RIF (G4) tests were performed to determine sensitivity and agreement with this test for TB detection. The sensitivities using a composite reference standard, pDST, and sequencing were >90% for INH, FLQ, amikacin (AMK), kanamycin (KAN), and capreomycin (CAP) resistance, meeting the WHO target product profile criteria for this class. A lower sensitivity of 65.9% (95% CI: 57.1–73.6) for ETH resistance was observed. The Xpert MTB/XDR showed a sensitivity of 98.3% (95% CI: 96.1–99.3) and specificity of 100% (95% CI: 86.7–100) compared with culture, a positive percent agreement (PPA) of 98.8% (95% CI: 93.7–99.8) and negative percent agreement (NPA) of 100.0% (95% CI: 78.5–100.0) compared with G4, and a PPA of 99.5% (95% CI: 97.3–99.9) and NPA of 100.0% (95% CI: 78.5–100.0) compared with Xpert MTB/RIF Ultra for detecting Mycobacterium tuberculosis . The test offers a promising solution for the rapid detection of drug-resistant TB and could significantly enhance control efforts in this setting.