Yes. There are about 10 to 15 million people in the United States, and many more world wide, who have a latent form of TB infection. They have been exposed to the bacteria and their body's immune system has confined it to a few of their cells, in an inactive form. Patients with latent TB infections are not sick and they are not infectious, but the TB bacteria is still there and still alive and, if they were tested, most would have a positive TB skin test. The majority of those with latent TB infection, about 90%, will never progress to active tuberculosis disease.

Those who do have active TB may not feel ill at first. Early symptoms may be subtle and, if the TB is extrapulmonary (outside of the lungs in organs such as the kidney and bone), the tuberculosis may be fairly advanced by the time it is causing noticeable symptoms.