IGRA (QuantiFERON-TB Gold Plus) is positive in a 30-year-old healthcare worker. TST (Mantoux) is also 18 mm. The worker has no symptoms, normal CXR, and no prior BCG record. How should these results be interpreted?
- A Latent TB infection (LTBI) — assess eligibility for preventive therapy (TPT) with isoniazid 6H or 3HP ✓
- B Active TB — start 4-drug HRZE regimen immediately
- C False-positive IGRA as BCG vaccination causes it
- D BCG vaccination false positive TST only; no treatment needed
Correct answer: A. Latent TB infection (LTBI) — assess eligibility for preventive therapy (TPT) with isoniazid 6H or 3HP
Explanation
Concordant positive IGRA and TST with no symptoms and normal CXR in a healthcare worker indicates latent TB infection (LTBI); IGRA is not affected by BCG vaccination (unlike TST). WHO and RNTCP recommend tuberculosis preventive therapy (TPT) for LTBI in high-risk groups including healthcare workers — options include isoniazid 6 months (6H), or rifapentine + isoniazid weekly × 12 doses (3HP). Active TB must be excluded before starting TPT. IGRA is BCG-unaffected because it uses ESAT-6/CFP-10 antigens absent from BCG.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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