RESUMEN
Tuberculin skin tests were performed on 1,146 patients out of an active patient population of 3,112 patients over a ten-year period in a rural western New York State family practice. There were 19 new positive tuberculin reactions and six cases of active tuberculosis discovered in the population. All but two of the patients with new positive tuberculin reactions and all of the patients with new cases of active tuberculosis were members of at least one of the following high-risk groups: (1) contract with an individual with active tuberculosis, or a positive family history of the disease; (2) immigrants to the United States; (3) a history of alcohol abuse; (4) having lived in an institutional setting; (5) health care personnel; and (6) having signs and symptoms of tuberculosis (cough, anorexia, weight loss, positive chest roentgenogram). All new cases of active tuberculosis were diagnosed because of symptoms. No asymptomatic person with a positive tuberculin test developed active disease during the study period. The positive predictive value of using risk factors to prescreen for the tuberculin skin test was 16 percent. The negative predictive value of not screening people without risk factors (because they will have a negative tuberculin test) was 99.8 percent.