Tuberculin skin test conversions and occupational exposure risk in US healthcare workers

Background. Healthcare workers (HCWs) undergo occupational tuberculosis screening at regular intervals. However, the risk of contracting tuberculosis at the workplace in a setting with a low background tuberculosis incidence is unclear. We aimed to evaluate the risk of tuberculin skin test (TST) conversion and the risk of occupational tuberculosis infection among HCWs in such a setting. Methods. We conducted a retrospective cohort study of employees of a large tertiary medical center in the US Midwest who had undergone TST screening during the study period 1 January 1998 to 31 May 2014. Results. Among 40 142 HCWs who received a TST, only 123 converted over 16.4 years. Only 9 (7%) of the converters had a suspected tuberculosis exposure at the workplace and none developed active tuberculosis. The majority of TST converters (66%) had a negative QuantiFERON-TB test at the time of the conversion. Conclusions. In one of the largest cohorts of HCWs in a low-tuberculosis-incidence setting, we demonstrated an extremely low risk of occupational tuberculosis exposure among TST converters and no resulting active tuberculosis cases. In this setting, the approach of testing HCWs at baseline and after tuberculosis exposure, rather than at regular intervals, should be considered.