Feasibility of Direct Sputum Molecular Testing for Drug Resistance as Part of Tuberculosis Clinical Trials Eligibility Screening

Abstract

A rapid diagnosis of drug-resistant tuberculosis (TB) is critical for early initiation of effective therapy. Molecular testing with line probe assays (MTBDRplus and MTBDRsl) on culture isolates has been available for some time and significantly reduces the time to diagnosis of drug resistance. However, routine use of this test directly on sputum is less common. As part of enrollment screening procedures for tuberculosis clinical trials conducted in Hanoi, Vietnam, we evaluated the feasibility and performance of line probe assay (LPA) testing directly on sputum samples from 315 participants with no prior history of TB treatment. Test performance characteristics for the detection of rifampin (RIF) and isoniazid (INH) drug resistance as compared to culture-based drug susceptibility testing (DST) reference standard were calculated. LPA demonstrated high sensitivity and specificity for the diagnosis of drug resistance. Scaling up molecular testing on sputum as part of time-sensitive clinical trial screening procedures in high TB burden settings is feasible and will reduce both time to initiation of appropriate therapy and the risk of late exclusions due to microbiologic ineligibility.

TB or not TB? Definitive determination of species within the Mycobacterium tuberculosis complex in unprocessed sputum from adults with presumed multidrug‐resistant tuberculosis

“…Sensitivity improves in people with conditions of known higher bacterial burden and expectedly decreases in paucibacillary conditions particularly in patients with atypical features of TB on chest radiograph [30,31]. Moreover, the high yield of gMTBC compared to smear microscopy supports its use during screening of participants in clinical trials [11]. Surprisingly in this study, approximately 45% of patients with a positive Xpert â MTB/RIF result for MTC had a negative LPA and LJ culture, as compared to only 20% from other studies [32].…”

“…Molecular methods including the gMTBC and sequencing technologies have been optimised for testing high burden samples such as cultured isolates [ 13 , 25 ]. Despite that the genotype MTBDRplus and MTBDRsl assays have recently been tested on unprocessed sputa [ 11 ], this is to our knowledge the first report to compare the performance with the gMTBC.…”

“…Sensitivity improves in people with conditions of known higher bacterial burden and expectedly decreases in paucibacillary conditions particularly in patients with atypical features of TB on chest radiograph [ 30 , 31 ]. Moreover, the high yield of gMTBC compared to smear microscopy supports its use during screening of participants in clinical trials [ 11 ].…”

“…The current molecular methods like Xpert® MTB/RIF (Cepheid, USA) and the line probe assays (LPA, Hain LifeScience, Germany) such as the genotype MTBDRplus and MTBDRsl have been endorsed by the World Health Organization (WHO) for detecting MTC and susceptibility to rifampicin, isoniazid, fluoroquinolone and second-line injectable drugs like aminoglycosides/capreomycin [ 10 ]. While WHO and a recent clinical trial have recommended use of the MTBDRplus and MTBDRsl in detecting MTC and drug resistance in direct sputum samples collected from patients with R/MDR-TB, they do not detect MTC to the species level [ 11 ]. The genotype MTBC assay (gMTBC) is a commercial platform (Hain LifeScience, Germany) that can address this gap, but it is only validated for testing cultured MTC isolates [ 12 , 13 ].…”

“…While building from the same principle of genotype MTBDRplus and MTBDRsl [ 11 ], we optimised and deployed the gMTBC assay to identify MTC to the species level from direct sputum samples of patients with presumed MDR-TB in Tanzania. We also performed comparative susceptibility testing of MTC species identified to rifampicin and isoniazid by using the genotype MTBDRplus, and to fluoroquinolones and second-line injectable drugs by using the genotype MTBDRsl.…”