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Xpert MTB/XDR assay: Rapid TB drug resistance detection

S K Dhatwalia(1) S Sethi(1) S Sharma(1) A N Aggarwal(1) R Rana(1) R Yadav(1)

1:Post Graduate Institute of Medical Education Research , Chandigarh

We aimed to evaluate the effectiveness of the Xpert MTB/XDR assay in rapidly detecting resistance to isoniazid, fluoroquinolones, ethionamide, and second-line injectable drugs among tuberculosis (TB) patients. Between August 2020 and July 2021, we enrolled samples from TB suspected patients at a tertiary care center for our investigation. Our study involved conducting mycobacterial culture and phenotypic drug susceptibility testing (DST) using the proportion method in liquid culture at WHO-recommended concentrations, alongside the Line Probe Assay. Concurrently, we performed the Index test, Xpert MTB/XDR, following the manufacturer's guidelines. Among 356 samples, 97 were excluded due to incomplete information. We found resistance to isoniazid, levofloxacin, and moxifloxacin in 45/251, 21/251, and 20/251 samples, respectively. The diagnostic accuracy of the Index test, with phenotypic DST as the reference standard, was 95.8%, 99.04%, and 99.05% for isoniazid, levofloxacin, and moxifloxacin, respectively. The Index test demonstrated a specificity of 99.1% for detecting second-line injectable drug resistance, resulting in a diagnostic accuracy of 99.2%. Compared to the line probe assays, the Index test showed improved sensitivity and specificity. Overall, the Index test showed promising results in identifying resistance to isoniazid and fluoroquinolones, outperforming the line probe assay, which could be crucial for promptly initiating treatment in cases of drug-resistant TB


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