Evaluation of a Rapid Molecular Drug-Susceptibility Test for Tuberculosis

Abstract

BACKGROUND Fluoroquinolones and second-line injectable drugs are the backbone of treatment regimens for multidrug-resistant tuberculosis, and resistance to these drugs defines extensively drug-resistant tuberculosis. We assessed the accuracy of an automated, cartridge-based molecular assay for the detection, directly from sputum specimens, of Mycobacterium tuberculosis with resistance to fluoroquinolones, aminoglycosides, and isoniazid. METHODS We conducted a prospective diagnostic accuracy study to compare the investigational assay against phenotypic drug-susceptibility testing and DNA sequencing among adults in China and South Korea who had symptoms of tuberculosis. The Xpert MTB/RIF assay and sputum culture were performed. M. tuberculosis isolates underwent phenotypic drug-susceptibility testing and DNA sequencing of the genes katG, gyrA, gyrB, and rrs and of the eis and inhA promoter regions. RESULTS Among the 308 participants who were culture-positive for M. tuberculosis, when phenotypic drug-susceptibility testing was used as the reference standard, the sensitivities of the investigational assay for detecting resistance were 83.3% for isoniazid (95% confidence interval [CI], 77.1 to 88.5), 88.4% for ofloxacin (95% CI, 80.2 to 94.1), 87.6% for moxifloxacin at a critical concentration of 0.5 μg per milliliter (95% CI, 79.0 to 93.7), 96.2% for moxifloxacin at a critical concentration of 2.0 μg per milliliter (95% CI, 87.0 to 99.5), 71.4% for kanamycin (95% CI, 56.7 to 83.4), and 70.7% for amikacin (95% CI, 54.5 to 83.9). The specificity of the assay for the detection of phenotypic resistance was 94.3% or greater for all drugs except moxifloxacin at a critical concentration of 2.0 μg per milliliter (specificity, 84.0% [95% CI, 78.9 to 88.3]). When DNA sequencing was used as the reference standard, the sensitivities of the investigational assay for detecting mutations associated with resistance were 98.1% for isoniazid (95% CI, 94.4 to 99.6), 95.8% for fluoroquinolones (95% CI, 89.6 to 98.8), 92.7% for kanamycin (95% CI, 80.1 to 98.5), and 96.8% for amikacin (95% CI, 83.3 to 99.9), and the specificity for all drugs was 99.6% (95% CI, 97.9 to 100) or greater. CONCLUSIONS This investigational assay accurately detected M. tuberculosis mutations associated with resistance to isoniazid, fluoroquinolones, and aminoglycosides and holds promise as a rapid point-of-care test to guide therapeutic decisions for patients with tuberculosis. (Funded by the National Institute of Allergy and Infectious Diseases, National Institutes of Health, and the Ministry of Science and Technology of China; ClinicalTrials.gov number, NCT02251327.)

Drug‐resistant tuberculosis: An update on disease burden, diagnosis and treatment

“…However, focusing on rpoB mutations alone as a surrogate for rifampin resistance may lead to erroneous use of empiric regimens . The initial choice of regimens may be substantially improved by a novel assay (not yet marketed) that includes resistance‐conferring target sequences allowing prediction of additional resistance to isoniazid, fluoroquinolones and the second‐line injectables (SLID) …”

“…49 The initial choice of regimens may be substantially improved by a novel assay (not yet marketed) that includes resistanceconferring target sequences allowing prediction of additional resistance to isoniazid, fluoroquinolones and the second-line injectables (SLID). 50 The line-probe assays identify patients with active TB and resistance-conferring mutations for rifampin, isoniazid, SLID and fluoroquinolones with modest to high accuracy (e.g. Hain Lifescience, Nehren, Germany; AID Diagnostika, Straßberg, Germany).…”

Drug resistance mechanisms and drug susceptibility testing for tuberculosis

“…A preliminary evaluation of the automated cartridge among 308 subjects showed sensitivities of 83.3% (95% CI: 77.1–88.5) for INH, 87.6% (95% CI: 79.0–93.7) for MOX (CC: 0.5 mg/L), 96.2% (95% CI: 87.0–99.5) for MOX (CC: 2.0 mg/L), 71.4% (95% CI: 56.7–83.4) for KAN and 70.7% (95% CI: 54.5–83.9) for AMK, when compared to pDST. The specificity of the assay for the detection of phenotypic resistance was 94.3% or greater for all drugs except MOX at the higher CC considered (2.0 mg/L, specificity: 84.0%, 95% CI: 78.9–88.3) …”

“…The specificity of the assay for the detection of phenotypic resistance was 94.3% or greater for all drugs except MOX at the higher CC considered (2.0 mg/L, specificity: 84.0%, 95% CI: 78.9-88.3). 154…”

Xpert implementation in challenging scenarios: a brand-new car running on the same bumpy old roads

“…1 The latest versions of Xpert offer further improvements: Xpert-Ultra cartridges present even higher sensitivity (closer to that of liquid media), and are a fantastic tool for diagnosing paucibacillary TB and lethal presentations such as TB meningitis; 2 Expert Omni is a completely portable device, closer to a point-of-care test; and Xpert Xpand is a new generation of cartridges able to diagnose common mutations conferring resistance to isoniazid, fluoroquinolones and second-line injectables, making the diagnosis of extensively drug-resistant TB (XDR-TB) quicker and much simpler. 3 More advances and devices based on molecular biology are certain to appear in the years to come, and will probably transform our conceptual way of diagnosing and treating TB.…”