I was asked this question by a mother whose son had just gotten a TB skin test. Tuberculosis is a current problem. The population of our planet has now grown to over 6 billion people. At Grand Rounds at Packard Children's Hospital, we were reminded that one third of the people on the planet are infected with tuberculosis. TB is the third leading cause of death globally -- behind acute respiratory infections and malaria. (AIDS is number four). TB prevention, detection, and treatment remains a major public health priority.