Benefit of two-step PPD testing of new employees at a New York City hospital

Background: Recent concern about nosocomial transmission of tuberculosis has led hospitals to scrutinize employee tuberculin conversion rates. The Centers for Disease Control and Prevention recommends two-step testing of new employees to limit the booster phenomenon. The cost of such a program and its subsequent yield have not recently been examined. Methods: Employee health records were retrospectively reviewed of persons hired from 1993 and 1994 at St. Clareʹs Hospital in New York City, all of whom received two-step testing at time of initial employment. Results: Of 262 new employees, 107 (41%) had positive tuberculin results on initial testing. The results of 15 (9.7%) of the remaining 155 patients became positive on two-step testing administered 1 week later. Persons with a positive second test result were significantly more likely to be male or foreign born or to have received previous bacille Calmette-Guérin vaccination. Identification of these 15 persons and exclusion of them from probable subsequent conversion prevented an almost 50% increase in the annual conversion rate at our hospital, from 3.2% to 4.7%. Conclusion: Two-step tuberculin testing is an essential means of identifying persons with a baseline positive tuberculin test result, thus allowing accurate reporting of subsequent employee tuberculin conversions.