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Information on Pulmonary Tuberculosis

An acute or chronic infection caused by Mycobacterium tuberculosis, tuberculosis (TB) is characterized by pulmonary infiltrates, formation of granulomas with caseation, fibrosis, and cavitation. People living in crowded, poorly ventilated conditions are most likely to become infected.

In patients with strains that are sensitive to the usual antitubercular agents, the prognosis is excellent with correct treatment. However, in those with strains that are resistant to two or more of the major antitubercular agents, mortality is 50%.

Causes

A The TB bacterium is spread through the air; however, repeated exposure to the germs is usually necessary before a person will become infected. It is not likely to be transmitted through personal items, such as clothing, bedding, or other items that a person with TB has touched. Adequate ventilation is the most important measure to prevent the transmission of TB.

Signs and symptoms

• In primary infection, after an incubation period of from 4 to 8 weeks, TB is usually asymptomatic but may produce nonspecific symptoms, such as fatigue, weakness, anorexia, weight loss, night sweats, and low-grade fever.
• In reactivation, symptoms may include a cough that produces mucopurulent sputum, occasional hemoptysis, and chest pains.

Diagnosis

Diagnostic tests include chest X-rays, a tuberculin skin test, and sputum smears and cultures to identify M. tuberculosis. The following procedures aid diagnosis:

• Auscultation detects crepitant rales, bronchial breath sounds, wheezes, and whispered pectoriloquy.
• Chest percussion detects a dullness over the affected area, indicating consolidation or pleural fluid.
• Chest X-ray shows nodular lesions, patchy infiltrates (mainly in upper lobes), cavity formation, scar tissue, and calcium deposits; however, it may not be able to distinguish active from inactive TB.
• Tuberculin skin test detects TB infection. Intermediate-strength purified protein derivative (PPD) or 5 tuberculin units (0.1 ml) are injected intracutaneously on the forearm.

Treatment

Antitubercular therapy with daily oral doses of isoniazid, rifampin, and pyrazinamide (and sometimes ethambutol) for at least 6 months usually cures TB. After 2 to 4 weeks, the disease generally is no longer infectious. The patient can resume his normal lifestyle while taking medication.

Patients with atypical mycobacterial disease or drug-resistant TB may require treatment with second-line drugs, such as capreomycin, streptomycin, para-aminosalicylic acid, cycloserine, amikacin, and quinolone drugs.

Prevention

The prevention of TB depends on:

• avoiding contact with those who have the active disease
• using medications as a preventive measure in high-risk cases
• maintaining good living standards

New cases and potentially contagious patients are identified through proper use and interpretation of the tuberculin skin test.

A vaccine called BCG (Bacille Calmette-Guérin) is considered controversial because it isn't very effective in countries with a low incidence of TB. For this reason, BCG isn't usually given in the United States. However, it may be considered for children emigrating to countries where TB is prevalent.