
TB, or tuberculosis, is a disease caused by bacteria caused Mycobacterium tuberculosis. It is spread from person to person through the air. TB usually affects the lungs. TB can also affect other parts of the body, such as the brain, kidneys or the spine.
TB bacteria become active if the immune system can't stop them from growing. The active bacteria begin to multiply in the body and cause TB disease. Some people develop TB disease soon after becoming infected, before their immune system can fight the TB bacteria. Other people may get sick later, when their immune system becomes weak for some reason.
Babies and young children often have weak immune systems. People infected with HIV, the virus that causes AIDS, have very weak immune systems. Other people can have weak immune systems, too, especially people with any of these conditions:
substance abuse, diabetes mellitus, silicosis, cancer of the head or neck, leukemia or Hodgkin's disease, severe kidney disease, low body weight, certain medical treatments (such as corticosteroid treatment or organ transplants)