Mycobacterium simiae is found primarily in the southwestern United States, Israel, and Cuba, with tap water as its suspected reservoir. Our institution saw an increase in M. simiae isolates in 2001. An investigation into possible contaminated water sources was undertaken.

Environmental cultures were performed from water taps in the microbiology laboratory, patient rooms, points in the flow of water to the hospital, and patients' homes. Patient and environmental M. simiae were compared by PFGE.

Military treatment facility in San Antonio, Texas.

All patients with cultures positive for M. simiae between January 2001 and April 2002. Medical records were reviewed.

M. simiae was recovered from water samples from the hospital, patients' home showers, and a well supplying the hospital. A single PFGE clone was predominant among water isolates (9 of 10) and available patient isolates (14 of 19). There was an association between exposure to hospital water and pulmonary samples positive for the clonal M. simiae strain (P = .0018). Only 3 of 22 culture-positive patients met criteria for M. simiae pulmonary disease. Of them, two had indistinguishable M. simiae strains from tap water to which they were routinely exposed.

This represents an outbreak of M. simiae colonization with one nosocomial infection. It is only the second time that M. simiae has been recovered from hospital tap water and its first presentation in municipal water. This study raises issues about the need and feasibility of eliminating or avoiding exposure to M. simiae from tap water.