Tuberculosis (TB) is a serious infectious disease caused by the bacterium Mycobacterium tuberculosis. It primarily affects the lungs but can spread to other parts of the body through the bloodstream and lymphatic system. TB remains a global health concern due to its airborne transmission and rising drug-resistant strains.
Pathophysiology
TB bacteria are transmitted via the airborne route when an infected person coughs, sneezes, speaks, or sings, releasing tiny droplets containing the pathogen. Once inhaled, the bacteria reach the alveoli, where they can multiply and spread to nearby lymph nodes and beyond.
The immune system may contain the bacteria (latent TB) or fail to do so, leading to active TB disease.
Types of TB
- Latent TB Infection (LTBI) – Bacteria present but inactive; no symptoms; not contagious; risk of reactivation if immunity weakens.
- Active TB Disease – Bacteria multiply and cause symptoms; highly contagious.
Signs and Symptoms of Active TB
Key Symptoms:
- Night sweats
- Unexplained weight loss (anorexia)
- Chronic cough, sometimes with blood-tinged sputum (hemoptysis)
- Fever and chills
- Dyspnea (shortness of breath)
Memory Trick:
- T – Terrible cough with “blood tinged” sputum
- B – Bad infection: fever, night sweats, weight loss
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Risk Factors
- Close contact with someone who has active TB
- Weakened immune system (HIV, diabetes, cancer treatment)
- Poor living conditions or overcrowding
- Malnutrition
- Substance abuse
Diagnostics
1. Tuberculin Skin Test (TST/Mantoux Test)
- Intradermal injection of purified protein derivative (PPD)
- Read after 48–72 hours
- Positive result: induration ≥15 mm in healthy individuals (lower thresholds for high-risk groups)
2. Chest X-ray
- Looks for lung lesions or cavities consistent with TB.
3. Sputum Culture
- Early morning samples for 3 consecutive days
- Gold standard for confirming active TB
- Cultures are continued until 3 negative results are obtained
Treatment
TB treatment requires multiple antibiotics for several months to prevent resistance:
- First-line drugs: Isoniazid (INH), Rifampin (RIF), Ethambutol (EMB), Pyrazinamide (PZA)
- Duration: Typically 6–9 months for drug-sensitive TB
- Directly Observed Therapy (DOT) is recommended to ensure adherence
Infection Control & Precautions
Airborne precautions for suspected or confirmed TB
- Patient placed in negative pressure isolation room
- N95 respirators for healthcare workers
Family members should be tested
Patients should cover their mouth when coughing and wear a mask during transport
Prevention
- Bacille Calmette-Guérin (BCG) vaccine in countries with high TB prevalence
- Early detection and treatment of latent TB
- Public health screening for high-risk groups
Quick Reference Table: TB Overview
| Feature | Details |
|---|---|
| Cause | Mycobacterium tuberculosis |
| Transmission | Airborne droplets |
| Key Symptoms | Night sweats, weight loss, blood-tinged sputum, fever |
| Diagnosis | TST, chest X-ray, sputum culture |
| Treatment | Multi-drug antibiotics for 6–9 months |
| Precautions | Airborne isolation, N95 masks |
Frequently Asked Questions (FAQs)
1. Is TB contagious during latent infection?
No. Latent TB is not contagious, but it can become active later.
2. How long after starting TB treatment is a patient non-infectious?
Usually after 2–3 weeks of effective therapy, though confirmation is needed with negative sputum cultures.
3. Why does TB treatment take so long?
TB bacteria grow slowly and can remain dormant in tissues, requiring extended therapy to kill all bacteria.
4. Can TB affect organs other than the lungs?
Yes — TB can spread to bones, brain (TB meningitis), kidneys, and lymph nodes.
5. What is MDR-TB?
Multidrug-resistant TB is resistant to at least isoniazid and rifampin, requiring longer and more complex treatment.
