Tuberculosis

Tuberculosis (TB) is a contagious disease caused by the bacilli Mycobacterium tuberculosis, which usually attacks the lungs but can also attack the brain, spine, and other parts of the body. TB was once the leading cause of death in the United States but is much less deadly today due to the development of drugs and combination therapies to treat it; however, the development of drug-resistant strains of TB is cause for concern. Worldwide, TB remains a major cause of morbidity and mortality, particularly in Africa and South East Asia.

TB is spread primarily through the air, when a person with active TB puts the bacilli in the air through coughing or sneezing and other people breathe in the bacilli. When a person breathes in TB, the bacilli may settle in the lungs and from there can move to other parts of the body. TB is not a highly contagious disease, and in fact only 20% to 30% of people exposed to TB bacilli become infected. Infection is most common among people who have daily or frequent contact with a person with active TB, such as a family member or coworker. The symptoms of active TB include persistent cough, coughing up blood, weakness and fatigue, weight loss, chills, fever, and night sweats.

[Page 1046]The most common test for TB is a skin test that involves inserting a small amount of fluid under the skin of the forearm; after 2 or 3 days the skin test is ‘read’ by a health care worker to determine if it is positive or negative. A positive skin test generally indicates exposure to TB, but does not mean that the person has active TB. In fact, most people who test positive for TB have only an inactive or latent infection, meaning that they are not currently sick but that the TB bacilli are present in their body, so they are at heightened risk of developing TB later in their lives. Persons with latent TB have no symptoms and cannot spread the disease to others. Risk factors for developing active TB include age (babies and young children are at greater risk), gender (males are more at risk during infancy and after 45 years of age, women in adolescence and early adulthood), occupational exposure to silicosis, and stress. Any condition that weakens the immune system also places a person with latent TB at risk: Today a common cause of diminished immunity is infection with HIV, and the combination of the two diseases has worsened the global TB burden. Persons with latent TB infection are often advised to take medication to prevent the latent infection from becoming active, and persons known to have weakened immune systems are sometimes treated prophylactially if they have frequent contact with someone known to have active TB.

Active TB is usually treated with a combination of drugs, the most common of which include streptomycin, isoniazid, rifampin, ethambutol, thiacetazone, and pyrazinamide. In most cases, a course of treatment must be continued for at least 6 months to kill all the TB bacilli in a person's body. However, because the person often feels better with only a few weeks of treatment, he or she may cease to take medications on schedule, therefore risking the chance of becoming ill again and also of breeding drug-resistant strains of TB. Directly observed therapy, in which a TB patient takes medications in the presence of a health care worker, has become common for at least initial TB treatment and is recommended by both the Centers for Disease Control and Prevention (CDC) and the WHO.

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