Rapid assay accurately detects drug-resistant TB
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A rapid sputum-based assay accurately detected resistance to isoniazid, fluoroquinolones, ethionamide, amikacin, kanamycin and capreomycin in people with tuberculosis symptoms, showing its potential to diagnose drug-resistant TB.
Adam Penn-Nicholson, PhD, deputy head of the TB program at Geneva-based FIND — a nonprofit that supports the evaluation of publicly prioritized TB assays and the implementation of WHO-approved assays — and colleagues prospectively studied people presenting with TB symptoms and at least one risk factor for drug resistance at two sites in India and one site each in Moldova and South Africa.
The assay, Xpert MTB/XDR (Cepheid), was used as a reflex test to detect resistance in adults with positive results for Mycobacterium tuberculosis complex from July 31, 2019, through March 21, 2020.
A total of 714 patients were screened for eligibility, and 710 were enrolled. Of those, 491 (69%) were smear positive and 614 (87%) were culture positive. A total of 611 participants had results from both the Xpert MTB/XDR assay and the composite reference standard for any drug.
The median age of participants was 37 years, 35% were women and 16% were HIV positive. Of the 611 participants who had results from both tests, 494 (81%) had rifampicin resistance on Xpert MTB/XDR and 463 (76%) were smear positive.
Detection of resistance was 94% for isoniazid (460 of 488, 95% CI, 92-96), 94% for fluoroquinolones (222 of 235, 95% CI, 90-96), 54% for ethionamide (178 of 328, 95% CI, 50-61), 73% for amikacin (60 of 82, 95% CI, 62-81), 86% for kanamycin (181 of 210, 95% CI, 81-91) and 61% for capreomycin (53 of 87, 95% CI, 49-70).
“This rapid sputum-based assay has the potential to greatly improve diagnosis and management of [drug-resistant] TB worldwide,” the authors wrote. “Additional studies, including those to assess implementation approaches, will be crucial to define best-use cases for the Xpert MTB/XDR assay and ensure optimum impact in improving outcomes for [drug-resistant] TB patients.”
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