Most people with TB have TB infection. Tuberculosis is caused by Mycobacterium tuberculosis , a bacterium. Tuberculosis is found worldwide. Tuberculosis is spread from person to person through the air. People with TB disease of the lung spray the bacteria into the air when they cough, sneeze, talk, or laugh.
People nearby can breathe in the bacteria and become infected.
To become infected, a person usually needs to be exposed for a long time to air containing many TB bacteria. When a person breathes in TB bacteria, they lodge in the lungs and begin to multiply. From there, the bacteria sometimes move through the blood to other parts of the body, such as the kidneys, joints, and brain. In most cases, the infection is kept in check by the body's immune system. In most people who become infected, the body's immune system is able to fight the TB bacteria and stop them from multiplying.