A 40-year-old HIV-positive man (CD4 55 cells/μL) develops fever, night sweats, cough, and weight loss. CBNAAT (GeneXpert Ultra) on sputum is MTB detected with rifampicin resistance detected. Line probe assay (GenoType MTBDRplus) shows rpoB mutation (S531L) and inhA promoter mutation (C-15T). This resistance pattern indicates:
- A Rifampicin resistance only (treat as RR-TB with short regimen)
- B MDR-TB (resistance to rifampicin and isoniazid) ✓
- C Pre-XDR TB (additional fluoroquinolone resistance)
- D Extensive drug resistance (XDR-TB by WHO 2021 definition)
Explanation
The GenoType MTBDRplus assay detects mutations conferring rifampicin resistance (rpoB gene) and isoniazid resistance (katG for high-level, inhA promoter mutations for low-level isoniazid resistance). The S531L mutation in rpoB confers rifampicin resistance; the inhA promoter C-15T mutation confers low-level isoniazid resistance. Together these confirm MDR-TB (resistance to both rifampicin and isoniazid). Pre-XDR TB requires additional fluoroquinolone resistance (levofloxacin or moxifloxacin). XDR-TB (WHO 2021 redefinition) = MDR/RR-TB + fluoroquinolone resistance + resistance to bedaquiline or linezolid.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.