In most people who breathe in TB bacteria and become infected, the person's body is able to fight the infection and keep them from growing. The TB bacteria become dormant, and this is called latent TB infection. People with latent TB infection:
* have no symptoms
* don't feel sick
* can't spread TB to others
* usually have a positive skin screening test reaction
Many people who have latent TB infection never develop active TB disease. In these people, the TB bacteria remain in the body for a lifetime without causing disease. But, in others, especially those who have weak immune systems, the bacteria can become active and cause TB disease.