Evaluation of Xpert(®) MTB/RIF assay: diagnosis and treatment outcomes in rifampicin-resistant tuberculosis.

Abstract

The Xpert(®) MTB/RIF assay is endorsed by the World Health Organization for the detection of rifampicin (RMP) resistant tuberculosis (TB). To evaluate Xpert for its diagnostic accuracy in detecting RMP-resistant TB and its impact on treatment outcomes. Patients with available phenotypic drug susceptibility testing (DST) results and those in whom RMP-resistant pulmonary TB was diagnosed using Xpert were evaluated. The accuracy and turnaround time (TAT) of Xpert for determining RMP-resistant TB was calculated. The TATs for treatment between patients diagnosed with RMP-resistant TB using Xpert and those diagnosed without the assay (phenotypic DST group) were compared. In 321 patients, when phenotypic DST was used as the gold standard, Xpert sensitivity and specificity for RMP resistance diagnosis was respectively 100% and 98.7%; the positive and negative predictive values were respectively 86.2% and 100%. The Xpert group had a much shorter interval from initial evaluation to commencing second-line anti-tuberculosis treatment (64 vs. 2 days, P < 0.001), and negative conversion of mycobacterial cultures (197 vs. 62.5 days, P < 0.001) than the phenotypic DST group. Xpert was accurate at diagnosing RMP resistance in this setting with an intermediate TB burden and a low level of RMP resistance. Xpert might reduce disease transmission by reducing the sputum culture conversion times for patients with RMP-resistant TB.