Identification of rifampicin resistance using xpert MTB/RIF and MTBDR plus V2.0 for the greater Gauteng province: implications for patient care

Black, Marianne
Journal Title
Journal ISSN
Volume Title
An ongoing challenge in the control of tuberculosis (TB) is drug resistant TB, including rifampicin resistant (RIFr) TB and multidrug resistant (MDR) TB. South Africa’s current diagnostic algorithm for TB diagnosis employs the Xpert MTB/RIF (GXP) as the initial screening test for TB diagnosis and rifampicin (RIF) susceptibility, followed by submission of a second specimen for MTBDRplus, a line probe assay (LPA) to confirm RIFr TB and to determine isoniazid (INH) susceptibility. This study aimed to describe the distribution of rpoB mutation patterns as identified by LPA and GXP in Gauteng province, and compare RIF susceptibility results between LPA and GXP. The most common rpoB mutation detected by LPA and GXP in Gauteng occurred at codons 530-533. LPA ΔWT2, which was mostly INH sensitive (INHs), is more prevalent in Gauteng than in other parts of the world. The LPA ΔWT3,4,8 and GXP probe B,E is a probable extensively drug resistant (XDR) TB strain prevalent in Gauteng and shows value in investigating gene regions derived from these molecular assays. The overall concordance between RIF susceptibility results was 96.42% and for the molecular codon region for RIFr results, 99.27%. There were 68 discordant RIF results over the one-year period, with a majority being, LPA RIF sensitive (RIFs), GXP RIFr. Discordant GXP RIFr results detected by delayed probe hybridisation reached statistical significance. The management of discordant RIF susceptibility results should involve inputs from both clinician and laboratory. The laboratory may provide rpoB sequencing when the culture is available, report heteroresistance when appropriate, performing phenotypic RIF DST and/or MIC testing, and reviewing all results for possible GXP and LPA technical errors. The introduction of a unique LIS patient identifier is critical to identify discordant results and troubleshoot accordingly and highlights the importance of an LIS with a wellmaintained central data warehouse
A Research report submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in partial fulfillment of the requirements for the degree of Master of Medicine. Johannesburg, 2019