This medicine is used to prevent any activation of the infection in the future, but you are not infectious to others. If you have a positive skin test and an abnormal chest radiograph or symptoms of tuberculosis, you'll be treated for active disease. When you're diagnosed with active disease, you're infectious to others. You may be treated with three or four medicines for nine to 12 months. You'll need to take precautions with your family, and you'll be kept out of work until you're no longer infectious.
Active tuberculosis is much less common than skin test conversion.
If in the past you received BCG vaccine to prevent tuberculosis, you may have a mild reaction to the tuberculosis skin test, but you should still be tested. Usually, BCG reactions related to the tuberculosis skin test become less severe over time. If your skin test increases in size and intensity, it may indicate that you have been infected with tuberculosis, and you need to be treated. The BCG vaccine is not 100 percent protective, so you could still get tuberculosis even if you had the vaccination. Unless you recently had your yearly tuberculosis test, you should have a baseline tuberculosis skin test if you are exposed to a patient with active tuberculosis, especially if the disease wasn't recognized, and isolation and masks were not used.