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What Is Tuberculosis?

Tuberculosis, commonly referred to as TB, is a bacterial infection that can spread through the lymph nodes and bloodstream to any organ in your body but is usually found in the lungs. Most people who are exposed to TB actually never develop symptoms. The bacteria can live in an inactive form in the body. Medication can be given to help get rid of the inactive bacteria. However, if the immune system weakens, such as in people with HIV or as we age, the bacteria can activate. In their active state, TB bacteria cause death of tissue in the infected organs, possibly resulting in death.

Because the bacteria that cause tuberculosis are transmitted through the air, the disease can be quite contagious. However, it is nearly impossible to catch TB simply by passing an infected person on the street. To be at risk, you must be exposed to the organisms constantly, by living or working in close quarters with someone who has the active disease. Even then, because the bacteria generally stay dormant after they invade the body; only 10% of people infected with TB will ever come down with the active disease. The remaining 90% will show no signs of infection, nor will they be able to spread the disease to others. Dormant infections can eventually become active, though, so even people without symptoms should receive medical treatment.

Once widespread, TB became relatively rare with the help of antibiotics developed in the 1950s. Today, however, a new and highly resistant form has emerged, creating a public-health hazard in many large cities worldwide. If you have TB — in its active or dormant state — you must seek medical treatment.

What Causes It?

Tuberculosis is generally caused by exposure to microscopic airborne droplets containing the bacterium Mycobacterium tuberculosis. The disease is almost never transmitted through clothes, bedding or other personal items. Because most people with TB exhale only a few of these germs with each breath, you can contract the disease only if you are exposed to an infected person for a long time. If you spend eight hours a day for six months, or 24 hours a day for two months, with someone with an active case of TB, you have a 50% chance of getting infected.

People who are malnourished or who live in close quarters stand the greatest chance of contracting tuberculosis. Therefore, the conditions that accompany poverty, although not a cause of tuberculosis, certainly contribute to its ability to spread. Healthcare workers, long-term hospital patients, and prison workers or inmates also face a greater-than-normal risk of becoming infected with TB. The active form of the infection is more likely to occur in people with weakened immune systems, such as those with AIDS, or blood cancers, such as leukemia.

Medically Reviewed by Paul Enright, MD , July 2005.

SOURCES: Montefiore Medical Center, New York, NY. Centers for Disease Control. World Health Organization. National Library of Medicine.

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