Tuberculosis
System: Respiratory Infections · Parent MOC: MOC - Diseases by System
One-Sentence Definition
Tuberculosis (TB) is a chronic granulomatous infection caused by Mycobacterium tuberculosis complex, transmitted by airborne droplets, with latent infection (LTBI) and active pulmonary or extrapulmonary disease forms.
Clinical Presentation
- Pulmonary: chronic cough, hemoptysis, weight loss, night sweats, fever
- Extrapulmonary: lymphadenitis, pleural, CNS, bone, disseminated (miliary) in immunosuppression
- LTBI: asymptomatic; positive IGRA/TST without active disease features
Pathogens
| Form | Organism | Notes |
|---|---|---|
| Typical TB | Mycobacterium tuberculosis | Acid-fast; slow growth |
| Related | M. bovis, M. africanum | Region/epidemiology dependent |
| Mimics | Nontuberculous Mycobacteria | Different treatment — do not assume TB |
Pathogenesis
- Inhalation → alveolar macrophages → granuloma (cell-mediated Adaptive Immunity)
- Latency vs reactivation (HIV, TNF inhibitors, malnutrition)
- Cavitation → high transmissibility
Diagnosis
| Step | Test | Note |
|---|---|---|
| Screening | IGRA or TST | LTBI programs |
| Active pulmonary | Sputum Acid-Fast Stain + mycobacterial culture | Gold standard for culture/AST |
| Rapid | NAAT (e.g., Xpert MTB/RIF) | Detects MTBC + rifampin resistance marker |
| Resistance | Culture AST + WGS in reference labs | MDR/XDR/XDR-TB epi |
| Imaging | Chest X-ray/CT | Cavities, miliary pattern |
Treatment Principles
- Active TB: multi-drug regimen (RIPE backbone) for months — public health supervised
- LTBI: shorter rifamycin-based regimens when indicated
- MDR-TB: individualized per AST/WGS
- Isolation + contact investigation (Infection Prevention and Control)
Prevention
- BCG (variable efficacy; policy by country)
- Treat LTBI in high-risk contacts
- Ventilation in high-risk settings
Differential / Pitfalls
- NTM lung disease; fungal; malignancy
- Xpert negative does not exclude paucibacillary TB — repeat/clinical judgment
- Do not treat LTBI and active disease with the same casual approach
Related
- Mycobacterium tuberculosis · HIV · Respiratory Infections
- MOC - Public Health & Epidemiology · MOC - Antimicrobial Resistance (AMR)
Active Recall
- Xpert MTB/RIF detects what besides MTBC?
- LTBI vs active TB — one diagnostic difference?
- Why is culture still important?