Definition

Tuberculosis is a chronic granulomatous disease that is spread primarily by aerosol transmission.

Incidence and prevalence

In the past and before specific antimicrobial therapy, tuberculosis was a significant cause of death and disability in North America. It currently affects approximately 28,000 persons in North America. Elderly, debilitated, and malnourished individuals, and people who are immunosuppressed and living in crowded conditions are most often affected.

Pathophysiology

Tuberculosis is caused by the acid-fast bacillus Mycobacterium tuberculosis. After being inspired, the bacilli multiply, causing nonspecific pneumonitis.

Some bacilli migrate to the lymph nodes, encounter lymphocytes, and precipitate the immune response. Phagocytes engulf colonies of bacilli in the lung, isolate them, and form granulomatous tubercles. Infected tissues inside the tubercles create caseation necrosis (a cheeselike material). Isolation of the bacilli is completed by formation of scar tissue around the tubercle. After approximately 10 days, the immune response is complete, and further bacilli multiplication is prevented. After isolation of bacilli and development of immunity, tuberculosis can remain dormant for life. Reactivation may occur if live bacilli escape into bronchi or in states of decreased immunity. Patients with laryngeal tuberculosis or lung cavitation have the highest infectivity rate.