An outbreak of seven cases (in six patients and one health care worker, all of whom had AIDS) of multidrug-resistant tuberculosis occurred in a hospital in Chicago. The hospital had a respirator-fit testing program but no acid-fast bacilli isolation rooms.To identify risk factors for transmission of Mycobacterium tuberculosis.Retrospective cohort study.Private hospital.Patients and health care workers exposed to M. tuberculosis.Analysis of M. tuberculosis isolates, tuberculin skin testing, assessment of exposure, and assessment of participant characteristics.All seven M. tuberculosis isolates had matching DNA fingerprints. Of patients exposed to M. tuberculosis, those who developed tuberculosis had lower CD4+ T-lymphocyte counts (P = 0.02) and were more likely to be ambulatory (P = 0.03) than those who did not. Of 74 exposed health care workers, the 11 (15%) who had conversion on tuberculin skin testing were no more likely than those who did not have conversion to report that they always wore a respirator with a high-efficiency particulate air filter.Transmission of M. tuberculosis occurred in a hospital that did not have recommended isolation rooms. A respirator-fit testing program did not protect health care workers in this setting.
