A nosocomial outbreak of multidrug-resistant tuberculosis

Background: 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. Objective: To identify risk factors for transmission of Mycobacterium tuberculosis. Design: Retrospective cohort study. Setting: Private hospital. Participants: Patients and health care workers exposed to M. tuberculosis. Measurements: Analysis of M. tuberculosis isolates, tuberculin skin testing, assessment of exposure, and assessment of participant characteristics. Results: 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. Conclusions: 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.