Tuberculosis: a disease of the 1990s.

In the United States, the decades preceding the 1980s were characterized by a decline in the incidence of tuberculosis. More recently, the trend has undergone a significant reversal: Case rates have been increasing by 3% to 6% annually. In 1990, more than 25,700 cases were reported to the Centers for Disease Control. In a sense, tuberculosis is adapting to the '90s. The recent increase in its incidence tends to affect populations with identifiable characteristics. Among the most important of these groups are the populations at high risk for infection by the human immunodeficiency virus. The increase is also fueled by cases in populations that are medically underserved, including foreign-born persons from high-prevalence countries, persons with low incomes, and persons living in long-term-care facilities--especially persons with previous tuberculosis infection. Thus, factors such as homelessness, chronic alcohol or drug abuse, malnutrition, and crowded living conditions continue to favor development and transmission of disease. The increase in the incidence of tuberculosis appears to be greatest when subpopulations in such circumstances are also at high risk for HIV infection. Complex issues in the diagnosis and treatment of tuberculosis arise from these epidemiologic patterns. HIV infection is associated with unusual presentations of tuberculosis. Thus, the clinician must maintain a high index of suspicion for the disease in the setting of HIV infection or risk of the infection. The populations at greatest risk are likely to be mistrustful of the medical system, making the long-term administration of potentially toxic chemotherapy more difficult than it already is. Chronic substance abuse may complicate compliance and add further difficulties to the monitoring of chemotherapy. At the same time, the monitoring becomes even more important in the physician's effort to minimize adverse effects of the medications. Outbreaks of drug-resistant disease have recently occurred, complicating the selection of drugs and affecting the duration of treatment. Despite all of these problems, it is essential to establish a diagnosis and initiate treatment rapidly, both to arrest the disease process and to limit its transmission. Since Mycobacterium tuberculosis is spread to uninfected persons in aerosols generated by coughing or sneezing, the infectiousness of a patient with active disease can be related, at least in part, to the number of organisms seen on sputum smears. Initiation of therapy is followed by a rapid decline in infectivity.