Difference between TB infection and TB disease

In most people who become infected, the body’s immune system is able to fight the TB bacteria and stop them from multiplying. The bacteria are not killed, but they become inactive and are stored harmlessly in the body. This is TB infection. People with TB infection have no symptoms and cannot spread the infection to others. However, the bacteria remain alive in the body and can become active again later.

If an infected person’s immune system cannot stop the bacteria from multiplying, the bacteria eventually cause symptoms of active TB, or TB disease. To spread TB to others, a person must have TB disease.

Most people who have TB infection never develop TB disease. But some infected people are more likely to develop TB disease than others. They include babies and children, persons with weak immune systems, and persons with some other kinds of lung disease. These people should take medicine to keep from developing TB disease. This is called preventive therapy.

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