A procedure used for the baseline testing of persons who will periodically receive tuberculin skin tests (e.g., HCWs) to reduce the likelihood of mistaking a boosted reaction for a new infection. If the initial tuberculin-test result is classified as negative, a second test is repeated 1-3 weeks later. If the reaction to the second test is positive, it probably represents a boosted reaction. If the second test result is also negative, the person is classified as not infected. A positive reaction to a subsequent test would indicate new infection (i.e., a skin-test conversion) in such a person. Ultraviolet germicidal irradiation (UVGI) The use of ultraviolet radiation to kill or inactivate microorganisms. Ultraviolet germicidal irradiation (UVGI) lamps Lamps that kill or inactivate microorganisms by emitting ultraviolet germicidal radiation, predominantly at a wavelength of 254 nm (intermediate light waves between visible light and X-rays). UVGI lamps can be used in ceiling or wall fixtures or within air ducts of ventilation systems.