Tuberculosis

Tuberculosis (TB)

1. Introduction

Tuberculosis (TB) is a chronic infectious disease caused mainly by the bacterium Mycobacterium tuberculosis. It primarily affects the lungs (pulmonary TB) but can also involve other organs such as lymph nodes, bones, kidneys, brain, and joints (extrapulmonary TB).

Several species belong to the genus Mycobacterium, including:

• Mycobacterium intracellulare
• Mycobacterium kansasii
• Mycobacterium bovis

However, Mycobacterium tuberculosis is the main pathogen responsible for TB in humans.

TB spreads from person to person through airborne droplets expelled when an infected person coughs, sneezes, laughs, or speaks.

In many healthy individuals, the immune system walls off the bacteria, resulting in latent TB infection, where bacteria remain inactive without symptoms. When immunity weakens (e.g., HIV infection, malnutrition, aging), the bacteria may become active and cause disease.

2. Epidemiology

Tuberculosis remains one of the most prevalent infectious diseases worldwide.

According to the World Health Organization:

• Millions of new TB cases occur each year globally.
• Developing countries carry the largest burden.
• India accounts for one of the highest numbers of TB cases in the world.

Factors contributing to high TB prevalence include:

• Poverty
• Malnutrition
• Overcrowding
• Poor living conditions
• Limited healthcare access

TB therefore remains a major public health problem, particularly in developing nations.

3. Etiology

Tuberculosis is caused by Mycobacterium tuberculosis.

Transmission occurs through airborne droplets released when a person with active TB:

• coughs
• sneezes
• speaks
• spits
• laughs
• sings

When these droplets are inhaled, the bacteria enter the lungs and initiate infection.

4. Risk Factors

Certain conditions increase the risk of TB infection or progression to active disease.

Major risk factors include:

• HIV/AIDS
• Frequent or prolonged contact with TB patients
• Malnutrition
• Poverty and overcrowded living conditions
• Immunocompromised states
• Diabetes mellitus
• Alcoholism
• Old age
• Chronic lung disease
• Smoking

5. Pathophysiology

Infection Process

1. TB bacteria enter the body through inhalation of droplet nuclei.
2. The bacteria reach the alveoli of the lungs.
3. Alveolar macrophages engulf the bacteria.
4. Instead of being destroyed, bacteria survive and multiply inside macrophages.
5. Infected macrophages release bacteria, triggering an immune response.
6. The immune system forms granulomas to contain the infection.

Granuloma Formation

Granulomas consist of:

• macrophages
• lymphocytes
• necrotic center (caseous necrosis)

The granuloma helps limit bacterial spread.

Latent TB Infection

In many individuals:

• Bacteria remain dormant
• Person has no symptoms
• Person is not infectious

However, the bacteria may reactivate later.

Active TB Disease

Active TB usually occurs when immunity weakens.

About 10% of people with latent TB develop active disease during their lifetime.

Risk is especially high in:

• HIV infection
• Patients receiving immunosuppressive therapy
• Those taking systemic corticosteroids or TNF-alpha inhibitors

6. Clinical Manifestations

Early Stage

During the initial infection, symptoms may be absent or mild.

Sometimes mild bronchial pneumonia may occur.

General Symptoms

Symptoms of chronic TB infection include:

• Loss of appetite (anorexia)
• Malaise (general feeling of illness)
• Weight loss
• Fatigue
• Low-grade fever
• Night sweats

Respiratory Symptoms

• Persistent cough lasting more than 2 weeks
• Sputum production (green, yellow, or blood-stained)
• Chest pain
• Shortness of breath
• Hemoptysis (coughing up blood)

Symptoms of Extrapulmonary TB

Symptoms depend on the organ involved.

Lymph nodes

• Swelling in neck or underarms

Bones and joints

• Pain and swelling, especially knee or hip

Genitourinary TB

• Flank pain
• Frequent urination
• Pain during urination
• Blood in urine

7. Diagnosis

Diagnosis involves clinical evaluation and laboratory tests.

Medical History and Physical Examination

Doctors assess symptoms such as:

• chronic cough
• fever
• fatigue
• night sweats
• weight loss

Laboratory Tests

Sputum Culture

• Confirms active TB infection
• Results may take 1–8 weeks

Sputum Microscopy

Examines sputum under a microscope to detect TB bacteria.

Mantoux Tuberculin Skin Test

A common test used to detect TB infection.

Procedure:

• Tuberculin is injected into the skin of the forearm.
• The reaction is checked after 48–72 hours.

A swelling at the site indicates possible infection.

TB Blood Test

Measures immune response to TB bacteria.

Useful when:

• Skin test results are uncertain
• Patient previously received TB vaccination

Chest X-Ray

Used to detect lung abnormalities such as:

• infiltrates
• nodules
• cavitation
• lesions

However, X-ray cannot confirm TB alone.

Rapid Molecular Tests

Rapid sputum tests can detect TB bacteria within 24 hours.

Diagnosis of Extrapulmonary TB

Additional tests may include:

Biopsy

• Tissue sample examined for TB bacteria

Urine culture

• Detects renal TB

Lumbar puncture

• Used to diagnose TB meningitis

CT scan

• Detects lung cavities or miliary TB

MRI scan

• Detects TB in brain or spine

Patients are also tested for:

• HIV infection
• Hepatitis

8. Anti-Tuberculosis Drugs

Treatment requires multiple drugs to prevent resistance.

First-Line Drugs

1. Isoniazid
2. Rifampicin
3. Ethambutol
4. Pyrazinamide
5. Streptomycin

These drugs are the most effective in TB treatment.

Second-Line Drugs

Used when resistance develops.

Examples include:

• Para-aminosalicylic acid
• Thiacetazone
• Ethionamide
• Cycloserine
• Kanamycin
• Rifabutin

New Drugs for Drug-Resistant TB

• Bedaquiline
• Delamanid
• Linezolid
• Sutezolid

Multidrug Resistant TB (MDR-TB)

Multidrug-resistant tuberculosis occurs when TB bacteria become resistant to isoniazid and rifampicin.

Treatment:

• Combination of second-line drugs
• Duration 18–24 months

9. Treatment Regimen

Short Course Therapy (6 Months)

Initiation Phase (First 2 Months)

• Isoniazid
• Rifampicin
• Pyrazinamide
• Ethambutol

Continuation Phase (Next 4 Months)

• Isoniazid
• Rifampicin

Long-Term Therapy (12 Months)

Used in complicated TB cases.

Initiation Phase

• Isoniazid
• Rifampicin
• Pyrazinamide
• Ethambutol

Glucocorticoids may be given for 2–3 weeks in severe inflammation.

Continuation Phase

• Isoniazid
• Rifampicin

for 10 months.

10. DOTS Strategy

The DOTS is recommended by the World Health Organization.

Five Components

1. Government commitment
2. Case detection by sputum microscopy
3. Standardized treatment under supervision
4. Continuous drug supply
5. Recording and reporting system

This strategy improves treatment success and prevents drug resistance.

11. Vaccination

BCG Vaccine

The BCG vaccine protects against severe TB in children.

Features:

• Given to newborn babies
• Common in countries with high TB prevalence
• Prevents severe childhood TB complications

12. Prevention

Health Education

• Encourage cough hygiene
• Use masks
• Improve ventilation
• Avoid crowded environments

Early Diagnosis and Treatment

Early treatment prevents:

• disease progression
• transmission to others

Healthy Lifestyle

• Balanced diet
• Regular exercise
• Adequate rest
• Avoid smoking and alcohol
• Maintain good ventilation

13. Spread of TB

TB spreads through air when infected individuals:

• cough
• sneeze
• laugh
• talk
• sing

Prolonged exposure in shared airspace increases infection risk.

14. TB Is NOT Spread By

TB does not spread through casual contact such as:

• shaking hands
• sharing utensils
• sharing food
• using public telephones
• brief contact on the street