During a TB case-finding survey in a rural village in Madhya Pradesh, a 42-year-old farmer with no respiratory symptoms is found to have a positive tuberculin skin test (TST, induration 15 mm) and a normal chest X-ray. He has no known TB contact history. His HIV status is negative. What is the most appropriate next step in management?

Explanation

## Clinical Scenario Analysis This patient has: - Positive TST (≥15 mm induration in non-immunocompromised individual) - Normal chest X-ray (no radiological evidence of active TB) - No respiratory symptoms - Negative HIV status - No known TB contact This clinical picture is consistent with **latent TB infection (LTBI)**, not active TB disease. ## Distinguishing Active TB from LTBI | Feature | Active TB | Latent TB Infection | |---------|-----------|--------------------| | TST/IGRA | Positive | Positive | | Chest X-ray | Often abnormal | Normal | | Symptoms | Present (cough, fever, night sweats) | Absent | | Sputum smear | May be positive | Negative | | Infectivity | Highly infectious | Non-infectious | | Management | Anti-TB drugs (4 drugs) | IPT (isoniazid alone) | **Key Point:** A positive TST with normal CXR and no symptoms = LTBI until proven otherwise. Active TB must be excluded before starting IPT. ## Diagnostic Algorithm for TST-Positive Individuals ```mermaid flowchart TD A[TST positive + normal CXR]:::outcome --> B{Symptoms of TB?}:::decision B -->|Yes| C[Sputum smear/GeneXpert]:::action B -->|No| D[Sputum smear/GeneXpert to exclude active TB]:::action C --> E{Active TB confirmed?}:::decision D --> E E -->|Yes| F[Start anti-TB therapy]:::action E -->|No| G[LTBI confirmed]:::outcome G --> H{Eligible for IPT?}:::decision H -->|Yes| I[Start isoniazid 6-9 months]:::action H -->|No| J[Observe, counsel on TB symptoms]:::action ``` **High-Yield:** GeneXpert MTB/RIF is the WHO-recommended rapid test for TB diagnosis. It detects TB DNA and rifampicin resistance simultaneously in <2 hours. ## Isoniazid Preventive Therapy (IPT) Eligibility **Mnemonic:** **CHIP** — **C**ontacts of TB, **H**IV-positive, **I**mmunosuppressed, **P**ositive TST with risk factors. In this case: - TST-positive ✓ - No HIV ✗ - No immunosuppression ✗ - No TB contact ✗ However, IPT is still recommended for TST-positive individuals in high TB-burden settings (India) as per NTEP guidelines, particularly in those aged 15–55 years without contraindications. **Clinical Pearl:** IPT reduces TB risk by ~60% in LTBI individuals. The standard regimen is isoniazid 5 mg/kg/day for 6–9 months. [cite:Park 26e Ch 7; NTEP Guidelines 2023]