TB is caused by a type of bacteria called Mycobacterium tuberculosis. TB usually affects the lungs, but can also affect other parts of the body. There are 2 forms of TB – active TB disease or latent TB infection.

A person with active TB disease in the lungs is infectious (i.e. can spread the disease to others), and will exhibit specific TB symptoms. A person with latent TB infection does not develop symptoms (e.g. cough) and does not spread TB to others.

The TB bacteria remain inactive in the body. About 5% of persons with latent TB infection may develop active TB disease in the first two years after being infected. For the rest, only 5% may develop active TB disease during the rest of their lifetime.

A person with active TB disease should be treated immediately. The decision to treat latent TB infection is made on a case by case basis.