Introduction
Tuberculosis (TB) is an infectious disease caused mainly by Mycobacterium tuberculosis. It most often affects the lungs (pulmonary TB) but can involve many other organs (extrapulmonary or miliary TB). TB spreads by tiny droplets when a person with active lung TB coughs, sneezes or speaks.
Epidemiology & Risk Factors
- TB is a major public health problem in India and many low-income countries.
- Risk is higher in people with HIV infection, malnutrition, diabetes, alcoholism, the elderly, close contacts of TB cases, and those on long-term immunosuppressive therapy.
Pathophysiology
After inhalation, bacilli reach alveoli and are taken up by alveolar macrophages. TB can survive inside macrophages and multiply. The immune response (TH1 cell–mediated) forms granulomas with a caseous (cheesy) centre to contain infection. This may result in:
- Clearance of bacteria
- Latent infection (no symptoms, positive immune tests)
- Progression to active disease (primary or reactivation TB)
Immunosuppression (for example HIV) increases the chance of progression from latent to active TB.
Clinical Features
- Chronic cough (>2 weeks) often with sputum, sometimes blood (haemoptysis)
- Fever (low grade), night sweats
- Weight loss, anorexia, fatigue
- Chest pain, shortness of breath in advanced disease
- Extrapulmonary signs depend on organ involved (lymph node swelling, spinal pain, urinary symptoms, meningitis signs, etc.)
Diagnosis
- Sputum microscopy & culture: Sputum AFB smear and culture remain standard; culture is more sensitive but slower.
- Rapid molecular tests: GeneXpert / NAAT detects TB DNA and rifampicin resistance quickly.
- Chest X-ray: Helpful for pulmonary TB (cavities, infiltrates).
- Tuberculin skin test (TST) / IGRA: Indicate infection (latent or prior exposure) but do not distinguish active disease.
- Drug susceptibility testing: Essential at diagnosis or if treatment failure is suspected to detect MDR/XDR TB.
- For extrapulmonary TB use biopsy, fluid analysis, imaging (CT/MRI) and site-specific cultures/PCR.
Treatment
Treatment uses multiple drugs to prevent resistance. Regimens depend on whether disease is drug-sensitive or drug-resistant.
First-line (drug-sensitive) — typical short course
- Intensive phase (2 months): Isoniazid (H) + Rifampicin (R) + Pyrazinamide (Z) + Ethambutol (E)
- Continuation phase (4 months): Isoniazid + Rifampicin (total 6 months)
When resistance or intolerance occurs
- Second-line drugs (e.g., fluoroquinolones, injectables like kanamycin/amikacin, cycloserine, ethionamide, linezolid) are used; treatment duration is longer (often 18–24 months) and guided by susceptibility testing.
- Newer drugs (bedaquiline, delamanid) are reserved for resistant cases under specialist care.
Programmatic Approach — DOTS
WHO-recommended DOTS (Directly Observed Treatment, Short-course) ensures adherence and includes government commitment, case detection, supervised treatment, reliable drug supply and recording/reporting. DOTS reduces default and drug resistance.
Complications
- Lung destruction, fibrosis and bronchiectasis
- Hemoptysis, pneumonia and respiratory failure
- Disseminated TB: meningitis, miliary TB, spinal TB (Pott’s disease), renal TB
- Drug toxicity (hepatitis, optic neuritis with ethambutol, renal toxicity with some drugs)
Prevention
- Early diagnosis and effective treatment of active cases to stop transmission
- BCG vaccination in newborns (protects against severe childhood TB)
- Screening and preventive therapy for high-risk contacts and people with latent infection (e.g., isoniazid preventive therapy)
- Improve ventilation, reduce overcrowding, good nutrition and control HIV
- Adhere to infection control measures in healthcare settings (masks, isolation when needed)
Detailed Notes:
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