Active Tuberculosis

It is important to understand that there is a difference between being infected with TB and having active TB. Someone who is infected with TB has the TB germs, or bacteria, in their body. The body's defences are protecting them from the germs and they are not sick.
Someone with active TB is sick and can spread the disease to other people. A person with active TB needs to see a doctor as soon as possible.

It is not easy to become infected with tuberculosis. Usually a person has to be close to someone with TB disease for a long period of time. TB is usually spread between family members, close friends, and people who work or live together. TB is spread most easily in closed spaces over a long period of time. However, transmission in an airplane, although rare, has been documented. Even if someone becomes infected with tuberculosis, that does not mean they will get TB disease. Most people who become infected do not develop active TB disease because their body's defences protect them.

The majority of people infected with mycobacterium tuberculosis never develop active TB. However, in the case of people with weakened immune systems, especially those infected with the human immunodeficiency virus (HIV, the cause of AIDS), TB organisms may overcome the body's defences, multiply, and cause active disease.