CDC has identified three risk categories in health-care settings:

• A low risk healthcare setting is one in which HCWs will most likely not be exposed to persons with TB disease or to clinical specimens that might contain M. tuberculosis.
• A medium risk healthcare setting is one in which the HCW will or might possibly be exposed to persons with TB disease or to clinical specimens that might contain M. tuberculosis.
• A potential ongoing transmission healthcare setting is temporarily applied to any setting if there is evidence of person-to-person transmission of M. tuberculosis in the past year.