Tuberculosis - Pulmonary

Definition

Pulmonary tuberculosis is a contagious bacterial infection caused by *Mycobacterium tuberculosis* affecting the lungs, characterized by chronic cough, hemoptysis, fever, night sweats, and weight loss.

Epidemiology

• Global burden: high prevalence in Asia, Africa, and parts of Eastern Europe.
• More common in adults aged 15–50 years, with a slight male predominance.
• Risk factors: HIV infection, malnutrition, diabetes, smoking, close contact with TB patients, immunosuppression.
• Incidence higher in crowded living conditions and low socioeconomic settings.
• BCG vaccination offers partial protection against severe TB in children.

Etiology

• *Mycobacterium tuberculosis* (acid-fast bacillus).
• Transmission via inhalation of airborne droplets from individuals with active pulmonary TB.
• Risk factors: immunocompromised states (HIV, steroids), malnutrition, diabetes, substance abuse.
• Previous TB infection or latent TB increases risk of reactivation.

Pathophysiology

• Inhaled bacilli reach alveoli and are phagocytosed by macrophages.
• Mycobacteria evade immune destruction, forming granulomas (tubercle) with central caseation.
• Cell-mediated immunity (T-cell response) contains infection in latent TB.
• Active disease occurs when granulomas fail to contain bacilli, leading to pulmonary tissue destruction, cavitation, and spread via airways.
• Systemic inflammatory response causes fever, weight loss, and night sweats.