http://www.cdc.gov/tb/pubs/tbfactsheets/exposure_eng.htm
National Center for HIV, STD, and TB Prevention, Centers for Disease Control and Prevention
You may have been exposed to tuberculosis (TB) if you spent time near someone with TB disease of the lungs or throat. This fact sheet provides basic information about TB exposure, including how one is exposed to TB and how to know if one has TB infection.