Minimizing tuberculosis risk to hospital personnel and students exposed to unsuspected disease.

A 15-month prospective study of the personnel and students exposed to initially unsuspected active cases of tuberculosis was undertaken to define the risk of their acquiring infection. Eight of 484 (1.65%) personnel exposed to 17 initially unsuspected tuberculosis patients and 5 of 2013 (0.25%) unexposed personnel with similar risk but no known exposures developed positive tuberculin skin tests. This greater than sixfold increase in conversion rate for the exposed group was significant (chi-2=14.83; P=0.0003). Delay in making the diagnosis in these patients was associated with failure to apply a tuberculin skin test on admission in 14 patients and radiologic misinterpretation in 15. A comprehensive surveillance method involving the Employee and Student Health Departments as well as the Public Health Department is suggested to minimize the risk of undiagnosed tuberculosis.