In most people who breathe in TB bacteria and become infected, the body is able to fight the bacteria to stop them from growing. The bacteria become inactive, but they remain alive in the body and can become active later. This is called TB infection. People with TB infection:

• have no symptoms
• don’t feel sick
• can’t spread TB to others
• usually have a positive skin test reaction

Can develop TB disease later in life if they do not receive preventive therapy
Many people who have TB infection never develop TB disease. In these people, the TB bacteria remain inactive for a lifetime without causing disease. But in other people, especially people who have weak immune systems, the bacteria become active and cause TB disease.