Annual tuberculin skin testing of employees at a university hospital: a cost-benefit analysis. 
The usefulness of routine annual tuberculin skin testing (purified protein derivative [PPD]) of hospital employees has been questioned.  Between 1984 and the end of 1987 the PPD conversion rates of hospital employees at a university and psychiatric hospital in North Florida were compared.  The number of employees in both hospitals were almost equal and compliance with the annual testing was more than 95%.  In the psychiatric hospital tuberculosis screening of patients was practiced on admission and annually thereafter.  Although no unsuspected smear-positive tuberculosis patients were diagnosed in the psychiatric hospital as compared to four in the university hospital, the annual conversion rates of employees were 0.42% and 0.13%, respectively (p greater than 0.001).  However, the ratios of these conversion rates to the incidence of tuberculosis in the counties where these hospitals are located respectively were similar (20.0 vs 24.3, p = 0.7).  The community seems be the major source of the PPD conversion.  At the university hospital more than +70,000 was spent on the annual PPD testing to discover 15 converters; nine had no or minimal contact with patients and only two complied with isoniazid (INH) prophylaxis.  Annual PPD testing is not cost effective in hospitals with a low annual conversion rate among its employees and with low tuberculosis case rates in the hospital and the surrounding community.