Tuberculin skin testing surveillance of health care personnel.

To estimate the incidence of and assess risk factors for occupational Mycobacterium tuberculosis transmission to health care personnel (HCP) in 5 New York City and Boston health care facilities, performance of prospective tuberculin skin tests (TSTs) was conducted from April 1994 through October 1995. Two-step testing was used at the enrollment of 2198 HCP with negative TST results. Follow-up visits were scheduled for every 6 months. Thirty (1.5%) of 1960 HCP with >/=1 follow-up evaluation had TST conversion (that is, an increase in TST induration of >/=10 mm). Independent risk factors for TST conversion were entering the United States after 1991 and inclusion in a tuberculosis-contact investigation in the workplace. These findings suggest that occupational transmission of M. tuberculosis occurred, as well as possible nonoccupational transmission or late boosting among foreign-born HCP who recently entered the United States. These results demonstrate the difficulty in interpreting TST results and estimating conversion rates among HCP, especially when large proportions of foreign-born HCP are included in surveillance.