Updates in Second-Line Genotypic Drug Susceptibility Tests

Multidrug-Resistant Tuberculosis Workshop
UPDATES IN SECONDI-LINE GENOTYPIC DRUG SUSCEPTIBILITY TESTS

Goon Ai Khiang
Pulau Pinang Hospital, Pulau Pinang, Malaysia

Drug-susceptibility tests (DSTs) are critical to the management of drug-resistant tuberculosis (DR-TB). Drug-susceptibility testing is the essential first step for the management of patients with DR-TB. Genotypic DST and phenotypic DST are complementary tests that are ordered as a pair when DR-TB is suspected. The GenoType and Xpert assays, which are WHO-recommended molecular rapid diagnostics (MRDs), are the main genotypic DST used in the country for the rapid diagnosis of DR-TB. A notable development in anti-TB DST this year is the introduction of Xpert MTB/XDR in the national TB programme and the advent of targeted next-generation sequencing in the country. This presentation will review the use of GenoType MTBDRplus and GenoType MTBDRsl as well as Xpert Ultra and Xpert MTB/XDR for detecting first- and second-line anti-TB drug resistance. It will cover important laboratory characteristics, from a clinical perspective, such as the basic principles of these assays, algorithms for the detection of drug resistance, test accuracy and recommendations for specimen/isolate testing. It will also discuss the WHO 2024 and alternative testing strategies using MRDs, and will compare the advantages/disadvantages of using MRDs, targeted NGS and mycobacterial growth indicator tube (MGIT) in decision pathways for the detection of DR-TB. Finally, this presentation will elucidate on the use and limitation of MRDs in the selection and modification of DR-TB based on the WHO 2022 update on the management of DR-TB and the WHO 2024 guidelines on the use of rapid diagnostics for tuberculosis detection