TB is short for tuberculosis, an infection usually spread by breathing in air that has been contaminated by someone with TB of the lungs. Most people who are exposed to TB don't get sick from it-the bacteria can live in the body for a long time without causing disease. But some people who carry the bacteria develop tuberculosis disease, and this is more likely if the immune system is weakened.

There are two types of tests to determine whether people are carrying the TB bacteria. One is the TB skin test (also known as PPD), which requires the person to return to the clinic 2-3 days after the skin test is placed for the test to be interpreted. The other is a blood test called an interferon-gamma release assay (IGRA) (QuantiFERON and TSpotTB are two examples of IGRA blood tests).

If a person tests positive for carrying the TB bacteria in their body, tests are done to determine whether it is currently causing infection of the lungs (which is contagious). Anyone with active TB should get an effective combination of medications to be cured. If, however, there is no active infection, antibiotics can be used to prevent trouble in the future. In this setting antibiotics are given for 3-9 months.