Click here to view next page of this article
One-third of the world population is currently infected with tuberculosis. Ten million newly infected individuals are diagnosed each year. The tuberculosis case rate in the United States is 9.4 cases per 100,000 population.
Pathophysiology
In most individuals infected with mycobacterium tuberculosis (by respiratory aerosols), the primary pulmonary infection occurs early in life, and the organism is contained by host defenses. The primary infection usually resembles pneumonia or bronchitis, and the infection usually resolves without treatment.
After the immune system limits spread of the bacilli during the primary infection, patients are typically asymptomatic, although the organisms may remain viable and dormant for many years. In these individuals, the only indication of primary infection is conversion to a positive reaction to the purified protein derivative (PPD) skin test. Acid-fast bacilli are not present in the sputum.
Later in life, the organism may cause reactivation disease, usually pulmonary, but it may affect the genitourinary system, bones, joints, meninges, brain, peritoneum, and pericardium. Reactivation of tuberculosis is the most common form of clinically apparent disease. Immunocompetent individuals with tuberculosis infection have a 10% chance of developing reactivation disease during their lifetimes. In HIV positive patients, the risk of acquiring active TB is 10% per year.
Reactivation disease is usually a chronic wasting illness. Nonspecific symptoms such as malaise, night Tuberculosis sweats, low grade fever, and weight loss may also occur.
Diagnosis of Active Pulmonary Tuberculosis
Chronic cough with scant sputum production and blood streaking of sputum are the most common symptoms of pulmonary disease. The pulmonary lesions eventually undergo central caseation necrosis.
Pulmonary tuberculosis should be considered in any patient with the following characteristics:
cough for more than 3 weeks
night sweats
bloody sputum or hemoptysis
weight loss
fever
anorexia
history of exposure to tuberculosis, institutionalization, HIV infection, or a positive PPD test.