Tuberculosis (TB): Transmission, Diagnosis, Treatment, and Global Burden

What Is Tuberculosis?

Tuberculosis (TB) is an infectious disease caused by Mycobacterium tuberculosis, an acid‑fast bacillus. It primarily affects the lungs (pulmonary TB) but can involve any organ (extrapulmonary TB).

Transmission and Natural History

• Airborne droplet nuclei (1–5 µm) expelled by coughing, sneezing, speaking.
• Inhalation → alveolar macrophages phagocytose bacilli → primary infection.
• Most infections become latent (LTBI): contained by granulomas, asymptomatic, non‑contagious.
• 5–10% progress to active disease (reactivation or primary progressive).

Clinical Features (Pulmonary TB)

• Persistent cough ≥2–3 weeks (may be productive, blood‑tinged)
• Fever, night sweats, weight loss, anorexia, fatigue
• Chest pain, dyspnea (if pleural involvement)
• Hemoptysis (late, cavitary disease)

Extrapulmonary TB

• Lymphadenitis (scrofula), pleural effusion, meningitis, pericarditis, Pott's disease (spinal), genitourinary, disseminated (miliary).

Diagnosis

• TST (Mantoux) or IGRA (Quantiferon/T‑SPOT) for latent infection.
• Sputum AFB smear (rapid, low sensitivity).
• NAAT (Xpert MTB/RIF Ultra) — WHO‑recommended initial test; detects DNA + rifampin resistance in <2 hours.
• Culture (solid/liquid) — gold standard; allows DST (drug susceptibility testing).
• Imaging (CXR, CT): upper lobe infiltrates, cavities, miliary pattern.

Treatment

Drug‑susceptible TB: 2‑month intensive phase (RIPE: Rifampin, Isoniazid, Pyrazinamide, Ethambutol) + 4‑month continuation (Rifampin, Isoniazid). Total 6 months. Directly observed therapy (DOT) recommended.

Drug‑resistant TB (MDR/XDR): Longer regimens (9–20 months) with second‑line drugs (bedaquiline, linezolid, clofazimine, fluoroquinolones, etc.) per WHO guidelines.

Prevention

• BCG vaccine (neonates in high‑burden countries; prevents severe pediatric forms).
• LTBI treatment (3–4 months rifampin‑based or 6–9 months isoniazid) for high‑risk contacts.
• Infection control: ventilation, UVGI, respirators (N95) in healthcare settings.

Global Burden

WHO 2023: ~10.6 million new cases, 1.3 million deaths. Leading infectious killer after COVID‑19. End TB Strategy targets 90% reduction in deaths by 2030.