Return of tuberculosis: screening and preventive therapy.

Approximately 25 percent of individuals exposed to Mycobacterium tuberculosis become infected. Of those, about 10 percent will develop clinically active tuberculosis at some time in their lives. The tuberculin skin test should be used to screen all patients, especially those at greatest risk of contracting the disease, such as the young and the old, and those with weakened immune systems from poor nutrition, alcohol and drug abuse, chronic illness and human immunodeficiency virus infection. Depending on the characteristics of the local population and individual medical risk factors, a reaction (induration) between 5 and 15 mm (or more) generally represents infection. Isoniazid therapy in persons with positive skin tests will decrease the risk of disease by 60 to 80 percent. Family physicians will play a critical role in efforts to eliminate tuberculosis from the United States by the year 2010.