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Step 1.1 – Establish a technical working group (TWG) and define roles and responsibilities
Step 1.2 – Review WHO policies and available technical and implementation guides
Step 1.3 – Define immediate and future purposes of the test
Step 1.4 – Update national diagnostic algorithm and guidelines
Step 1.5 – Perform a situational analysis, including biosafety
Phenotypic DST remains the reference standard for most anti-TB compounds; however, this method is slow, and it requires specialized infrastructure and highly skilled staff. Genotypic DST (also referred to as molecular DST) holds promise to overcome some of these obstacles. Currently, available WHO-recommended rapid molecular drug susceptibility tests (Section 2.4) can be used to detect specific mutations known to confer phenotypic resistance. Although genotypic DST has advanced over the past decade, the spectrum of drugs covered is limited and does not cover the new and repurposed drug.
Treatment of TB has undergone significant changes over recent years, with new drugs and regimens recommended; hence, the definitions for DR-TB have been revised accordingly. The updated pre-extensively drug-resistant TB (pre-XDR-TB) definition is “TB caused by M. tuberculosis strains that fulfil the definition of MDR/RR-TB and are also resistant to any FQ”, and the updated XDR-TB definition is “TB caused by M. tuberculosis strains that fulfil the definition of MDR/RR-TB and that are also resistant to any FQ and at least one additional Group A drug (i.e.
Targeted NGS tests couple amplification of selected genes with NGS technology to detect resistance to many drugs with a single test. Because targeted NGS tests can interrogate entire genes to identify specific mutations associated with resistance, targeted NGS tests may provide improved accuracy compared with other WRDs. In addition, new targeted NGS tests can detect resistance to new and repurposed drugs not currently included in any other molecular assays.
Table A.3.1. Guideline development group members: “Targeted next-generation sequencing” 2–5 May 2023
Bruker-Hain Diagnostics has two real-time nucleic acid amplification tests (NAATs), the FluoroType MTB to detect Mycobacterium tuberculosis complex (MTBC) and the FluoroType MTBDR, to detect MTBC, and resistance to rifampicin (RIF) and isoniazid (INH) in tuberculosis (TB). The MTB test (VER 1.0) targets the IS6110 DNA insertion element for MTBC detection, while the MTBDR test (VER 2.0) targets the rpoB gene for detection of MTBC and RIF resistance, and the inhA promoter and katG gene for detection of INH resistance.
The Xpert MTB/XDR detects Mycobacterium tuberculosis complex (MTBC) DNA and genomic mutations associated with resistance to isoniazid (INH), fluoroquinolones (FQs), ethionamide (ETH) and second-line injectable drugs (amikacin [AMK], kanamycin and capreomycin) in a single cartridge. Xpert MTB/XDR tests are run on Cepheid's GeneXpert instruments, using 10-colour modules that differ from the 6-colour modules traditionally used for Xpert MTB/RIF and Xpert MTB/RIF Ultra (Xpert Ultra) testing.
Nipro (Osaka, Japan) developed Genoscholar PZA-TB, a reverse hybridization-based technology for detection of pyrazinamide (PZA) resistance in tuberculosis (TB) (1, 2). Compared with MTBDRplus and MTBDRs/ LPA, the Genoscholar PZA-TB line-probe assay (LPA) does not include specific mutant probes, because resistance mutations are widespread across the entire pncA gene with no predominant mutations.