In developed countries, such as the United States, many people think tuberculosis (TB) is a disease of the past. TB, however, is still a leading killer of young adults worldwide. Some 2 billion people-one-third of the world's population-are thought to be infected with TB bacteria, Mycobacterium tuberculosis.
TB is a chronic bacterial infection. It is spread through the air and usually infects the lungs, although other organs and parts of the body can be involved as well. Most people who are infected with M. tuberculosis harbor the bacterium without symptoms (have latent TB), but some will develop active TB disease. According to World Health Organization (WHO) estimates, each year, 8 million people worldwide develop active TB and nearly 2 million die.
One in 10 people who are infected with M. tuberculosis may develop active TB at some time in their lives. The risk of developing active disease is greatest in the first year after infection, but active disease often does not occur until many years later.
TB in the United States
In 2005, the Centers for Disease Control and Prevention (CDC) reported 14,093 cases of active TB. While the overall rate of new TB cases continues to decline in the United States since national reporting began in 1953, the annual decrease in TB cases has slowed from an average of 7.1 percent (1993 to 2000) to the current average of 3.8 percent (2001-2005), according to CDC. In addition to those with active TB, an estimated 10 to 15 million people in the United States have latent TB.
Minorities are affected disproportionately by TB, which occurs among foreign-born individuals nearly nine times as frequently as among people born in the United States. This is partially because they were often exposed to M. tuberculosis in their country of origin before moving to the United States. In 2004, a very high percentage of Asians (95 percent) and Hispanics (75 percent) who were born outside the United States were reported to have TB.
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