Diagnostic Accuracy of LiquidArray MTB-XDR VER 1.0 for the Detection of Mycobacterium tuberculosis Complex, Fluoroquinolone, Amikacin, Ethambutol, and Linezolid Susceptibility.

BACKGROUND: Drug susceptibility testing (DST) is essential for starting people on effective tuberculosis (TB) regimens. No published data exist for the high-throughput LiquidArray MTB-XDR (LA-XDR) test, which detects Mycobacterium tuberculosis complex (MTBC) and fluoroquinolone, amikacin, ethambutol, and linezolid susceptibility (the latter 2 have no rapid DSTs available).

METHODS: We enrolled people (N = 720) with presumptive TB who provided 2 sputum samples for an Xpert MTB/RIF Ultra assay and a culture (MTBC reference standard). Phenotypic DST and Sanger sequencing were the composite reference standards. LA-XDR on the manual FluoroLyse and automated GenoXtract fleXT (fleXT) DNA extraction methods were compared.

RESULTS: For MTBC, LA-XDR had similar sensitivities (85%-87%) and specificities (99%) using each extraction method. Drug susceptibility sensitivities (95% confidence interval) varied: 94% (86%-98%) for fluoroquinolones, 64% (45%-80%) for amikacin, and 88% (79%-93%) for ethambutol (specificities of 97%-100%). Six of 7 (86%) resistant linezolid isolates were detected. LA-XDR with fleXT had indeterminate proportions of 21/251 (8%), 2/251 (1%), 63/251 (25%), and 93/251 (37%) for fluoroquinolones, ethambutol, amikacin, and linezolid, respectively (amikacin and linezolid indeterminates were higher with FluoroLyse-extracted DNA). In a hypothetical population of 100 smear-negative people with fluoroquinolone-resistant TB undergoing fleXT DNA extraction, 25 (25%) would be missed (1 extraction error, 2 invalid results, 15 MTBC-negative, 6 fluoroquinolone-indeterminate, and 1 false-susceptible).

CONCLUSIONS: LA-XDR met the minimum World Health Organization target product profile for a next-generation, sputum-based, moderate-complexity DST with high fluoroquinolone and ethambutol resistance sensitivity, moderate amikacin resistance sensitivity, and promise for linezolid resistance, for which more data are needed. Improved LA-XDR MTBC detection would reduce missed resistance.