Tuberculosis (TB): Causes, Latent vs. Active Disease, Diagnosis, and Treatment

Tuberculosis is caused by Mycobacterium tuberculosis, an acid-fast bacillus spread via airborne droplet nuclei from active pulmonary TB cases. It remains a global health emergency.

Latent TB Infection (LTBI)

• Immune system walls off bacilli in granulomas.
• Asymptomatic, non-infectious, TST/IGRA positive.
• 5–10% lifetime reactivation risk (higher with HIV, TNF-α inhibitors, diabetes, malnutrition).
• Treatment options: Isoniazid 9 months; 3HP (isoniazid+rifapentine weekly ×12); 4 months rifampin.

Active TB Disease

Pulmonary (80%):

• Cough >2 weeks, hemoptysis, weight loss, night sweats, fever, fatigue.

Extrapulmonary:

• Lymph nodes, pleura, spine (Pott's disease), meninges, kidneys, disseminated (miliary).

Diagnosis

• Sputum AFB smear (rapid, low sensitivity)
• NAAT (GeneXpert—rapid, detects rifampin resistance)
• Culture (gold standard, drug susceptibility testing)
• CXR: upper lobe infiltrates, cavities

Treatment (Drug-Susceptible)

Intensive phase (2 months): RIPE (Rifampin, Isoniazid, Pyrazinamide, Ethambutol).
Continuation phase (4 months): Rifampin + Isoniazid.
Total 6 months. DOT (directly observed therapy) recommended.

Drug-Resistant TB

• MDR-TB: Resistant to rifampin + isoniazid. Requires 9–12 month all-oral regimens (bedaquiline, linezolid, etc.).
• XDR-TB: Adds resistance to fluoroquinolones + injectables.

Key Principles

• Early diagnosis stops transmission.
• Complete treatment prevents resistance.
• LTBI treatment prevents future active disease.
• HIV coinfection requires integrated care.

TB is curable—but only with adherence, proper regimens, and public health infrastructure.