Many people think tuberculosis (TB) is a disease of the past. But, TB is still a leading killer of young adults worldwide. Some 2 billion people – one-third of the world's population – are infected with the TB bacterium, M. tuberculosis. TB is a chronic bacterial infection. It is spread through the air and usually infects the lungs, although other organs are sometimes involved. Most persons that are infected with M. tuberculosis harbor the bacterium without symptoms but many develop active TB disease. Each year, 8 million people worldwide develop active TB and 3 million die.

In the United States, TB has re-emerged as a serious public health problem. In 2001, based on provisional data reported to the U.S. Centers for Disease Control and Prevention, the number of cases has decreased for the ninth straight year to 15,991 cases of active TB (infection with full-blown disease symptoms). This all-time low is due largely to improved public health control measures. In addition to those with active TB, however, an estimated 10 to 15 million people in the United States are infected with M. tuberculosis without displaying symptoms (latent TB) and about one in ten of these individuals will develop active TB at some time in their lives.

Minorities are affected disproportionately by TB: 54 percent of active TB cases in 1999 were among African-American and Hispanic people, with an additional 20 percent found in Asians.

Cases of TB dropped rapidly in the 1940s and 1950s when the first effective antibiotic therapies for TB were introduced. In 1985, however, the decline ended and the number of active TB cases in the United States began to rise again. Several forces, often interrelated, were behind TB's resurgence:
The HIV/AIDS epidemic. People with HIV are particularly vulnerable to turn infection with M. tuberculosis into active TB and are also more sensitive to developing active TB when they are first infected with the TB germ.

Increased numbers of foreign-born nationals from countries where many cases of TB occur, such as Africa, Asia, and Latin America. TB cases among those persons now living in the US account for nearly half of the national total.

Increased poverty, injection drug use, and homelessness. TB transmission is rampant in crowded shelters and prisons where people weakened by poor nutrition, drug addiction, and alcoholism are exposed to M. tuberculosis.
Failure of patients to take their prescribed antibiotics against TB as directed.
Increased numbers of residents in long-term care facilities such as nursing homes. Many develop active TB from infections with M. tuberculosis that occurred much earlier in life because their general health has declined. Other elderly people, especially those with weak immune systems, become newly infected with M. tuberculosis and can rapidly develop active TB.

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