People who are infected with TB bacteria (Mycobacterium tuberculosis) but are not sick have a condition called latent TB infection. A person with latent TB infection does not have symptoms and cannot spread TB bacteria to others. Many people who have latent TB infection never develop TB disease. Some people develop TB disease soon after becoming infected (within weeks) before their immune system can fight the TB bacteria. Other people may get sick with TB disease years later when their immune system becomes weak for another reason. Latent TB infection can be treated to prevent the development of TB disease.