A patient on standard first-line TB treatment (HRZE) for 2 months has a persistently positive sputum culture. DST reveals isoniazid resistance (katG mutation) with preserved rifampicin susceptibility. This is classified as:
- A Isoniazid-resistant TB (Hr-TB) ✓
- B Multidrug-resistant TB (MDR-TB)
- C Pre-XDR TB
- D Rifampicin-resistant TB (RR-TB)
Correct answer: A. Isoniazid-resistant TB (Hr-TB)
Explanation
WHO 2022 definitions: Isoniazid-resistant, rifampicin-susceptible TB is termed Hr-TB (isoniazid-resistant TB) and is managed with a standard 6-month regimen of rifampicin, ethambutol, pyrazinamide, and levofloxacin (without isoniazid). MDR-TB requires resistance to both isoniazid AND rifampicin. RR-TB indicates rifampicin resistance (with or without isoniazid resistance). Pre-XDR TB is MDR/RR-TB with additional resistance to any fluoroquinolone. Correct classification determines the treatment regimen and prevents inappropriate monotherapy.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
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