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Clusters of Multidrug-Resistant Tuberculosis

TO THE EDITOR: We wish to clarify a point made in our report on multidrug-resistant tuberculosis in the United States. By noting that clusters of multidrug-resistant tuberculosis cases had been reported from 12 U.S. hospitals [1], we did not mean that nosocomial transmission had been verified in each. Hospital clusters may result from outbreaks caused by transmission inside or outside the hospital. Transmission in the hospital may be implicated by epidemiologic associations between exposure in the hospital and the subsequent development of disease or by the demonstration of molecular genetic similarity between patient isolates [1]. As of 18 September 1992, clusters of multidrug-resistant tuberculosis were reported in 15 institutions, including 14 hospitals [1-3] (Centers for Disease Control. Unpublished data) and a prison system [4]. To date, investigations have implicated nosocomial transmission in eight of these institutions, including seven hospitals. Multidrug-resistant tuberculosis has been confirmed in at least 241 patients and 17 health care workers in these institutions. Control of nosocomial tuberculosis will require careful adherence to preventive measures [5].