Abstract

Because of declining prevalence of tuberculosis in the United States, standard laboratory tests detect fewer actively infected patients. Of 6,884 cultures for Mycobacterium tuberculosis (MTB) in three years at our hospital, only 2% were positive. To select other effective screening variables, we retrospectively reviewed patients in whom cultures were ordered. Charts of 79 patients with active tuberculosis and 226 patients whose cultures were negative were reviewed for 45 signs, symptoms, and laboratory tests determined at the time of initial contact. Those variables which distinguished the MTB-active from the nonactive were: history of weight loss, prior exposure, night sweats, fever, abnormal chest roentgenogram, positive skin test (PPD) (at P< .001), and cough and abnormal pulmonary examination (at P< .05). An algorithmic analysis suggests that weight loss and/or cough, followed by abnormal chest x-ray film and/or positive PPD, would detect 77% of the MTB-infected persons in whom these tests were done. The classic signs and symptoms of pulmonary tuberculosis continue to be excellent screening variables. When combined with the chest x-ray film and PPD, they may allow use of the culture as a confirmatory test, rather than its current inappropriate use as a screening test, for a disease of low prevalence.