any other infectious disease (Caldwell, 1987; Murray et al., in press). Each year, according to the WHO, 8 million new cases of clinical TB are diagnosed, and 2.9 million people die of the disease. In the United States, until 1985, TB incidence had been in decline for more than three decades. Between 1986 and 1991, however, 28,000 more cases were reported than were predicted to occur based on past experience.

TB is a bacterial disease whose principal manifestation is destruction of lung tissue; it is spread primarily through the respiratory route by patients with active pulmonary disease. One out of every 10 to 12 healthy individuals infected with the tubercle bacillus develops clinical disease. The case fatality rate of untreated TB in people with clinical disease is 50 percent, and their average life span is six months to two years.

Multiple factors are contributing to the rise in cases of TB. Of major importance are increased poverty and a growing number of homeless individuals and families, substance abuse, a deteriorating health care infrastructure for treating chronic infectious diseases, and the HIV disease pandemic (perhaps the most significant factor at present). Complacency within the medical community and among the public at large and shortages of the drugs used to treat TB are additional factors in the increase.

TB is difficult to treat. Multidrug therapy is invariably necessary, with the drugs administered over at least six months to effect a clinical cure and prevent the emergence of drug-resistant organisms. Where health care infrastructure is adequate and compliance with treatment is maintained, cure rates should exceed 90 percent, even in HIV-infected individuals who have TB, providing resistant organisms are not present. When treatment is either inappropriate or inadequate, resistance to one or more of the treatment drugs often develops. The increased finding of resistant organisms reflects a major breakdown in the social and health care infrastructures.

When multidrug-resistant TB is present, case fatality rates can exceed 80 percent in immunocompromised individuals (see Chapter 2). The presence of multidrug-resistant organisms puts not only TB-infected individuals but also health care workers, social workers, corrections officials, families, and contacts at risk of contracting a disease that is difficult or essentially impossible to treat. Multidrug-resistant TB now represents a major threat to health in the United States.

In the 1950s, with the advent of antituberculosis drugs, TB became one of several newly treatable infections diseases. The common assumption regarding such diseases has been that drugs that have been effective in treating them will continue to be so. Current experience with TB is causing many to question that assumption. Other organisms that have developed resistance to frontline drugs (probably for some of the same reasons) are also signaling the possibility of trouble ahead. Penicillin-resistant streptococcal Group A and Group C infections and penicillin-resistant pneumococcal



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