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Rifampicin Resistance Full DST — SCE Infectious Diseases MCQ

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ModerateTuberculosisRifampicin Resistance Full DSTSCE Infectious Diseases

A 45-year-old man with HIV on ART develops new bilateral groin lymphadenopathy. FNA shows granulomata. AFB stain is positive. GeneXpert confirms M. tuberculosis with Rifampicin resistance detected. What additional resistance testing is needed?

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Correct answer: A — Full line-probe assay (Hain GenoType MTBDRplus/sl) or whole-genome sequencing to detect additional mutations — Rifampicin resistance is a proxy for MDR-TB (resistance to both Rifampicin AND Isoniazid in ~80% of cases)

GeneXpert detects Rifampicin resistance via rpoB gene mutations but does NOT test for Isoniazid or second-line resistance. Rifampicin resistance is a proxy for MDR-TB (~80% of Rifampicin-resistant isolates are also Isoniazid-resistant). Full resistance profiling is essential: (1) line-probe assays (GenoType MTBDRplus for first-line; MTBDRsl for second-line — fluoroquinolones, aminoglycosides), (2) phenotypic DST on liquid culture (MGIT), (3) ideally whole-genome sequencing. MDR-TB regimens (BPaLM — Bedaquiline, Pretomanid, Linezolid ± Moxifloxacin) are guided by comprehensive resistance data.

Reference: NICE NG33 2016 – TB; WHO 2022 – MDR-TB; UKHSA 2024