Tuberculosis, commonly known as TB, is a bacterial infection spread through the air from a person who has active tuberculosis to those who are in close contact. It is most often found in the lungs.
Most people who are exposed to TB never develop symptoms because the bacteria can live in an inactive form in the body. But if the immune system weakens, such as in people with HIV or elderly adults, TB bacteria can become active. In their active state, TB bacteria cause death of tissue in the organs they infect. Active TB disease can be fatal if left untreated.