Evaluation of the Two-Step Tuberculin Skin Test in Health Care Workers at an Inner-City Medical Center

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Abstract
The increased rate of tuberculosis (TB) infection and transmission from patients to health care workers (HCWs) has brought awareness of the need for better surveillance programs. The two-step purified protein derivative (PPD) skin test decreases the misinterpretation of a "boosted reaction" as a recent infection with Mycobacterium tuberculosis in HCWs. We reviewed the medical records of 4082 HCWs at an inner-city medical center who had PPD skin-testing performed as a component of the TB medical surveillance program during the years 1994 and 1995. Of those HCWs tested, 3896 (95.4%) returned for the PPD skin-test evaluation. Of those 3896 HCWs, 3659 (93.9%) had a negative baseline PPD skin test, and 237 (6.1%) had a positive skin test. Of those HCWs with a negative baseline skin test, 252 (6.9%) were eligible for the second PPD skin test. Of the 241 who returned for their second PPD skin-test reading, six (2.5%) had positive results. All six cases were foreign-born physician residents with a previous history of Bacille bilié de Calmette-Guérin (BCG) vaccination. We conclude that the two-step PPD skin test method is not indicated for HCWs at this urban medical facility.