Nosocomial outbreak of respiratory tract colonization with Mycobacterium fortuitum: demonstration of the usefulness of pulsed-field gel electrophoresis in an epidemiologic investigation.

Between August 1989 and January 1990, 16 patients on an alcoholism rehabilitation ward (ARW) developed positive sputum cultures for Mycobacterium fortuitum. During a 2-wk surveillance period, six of 43 ARW patients but none of 20 staff members had positive sputum cultures. In addition, none of 54 patients and staff on an adjacent ward sharing the same ice machine and water supply had positive cultures, and none of 92 acid-fast bacilli cultures performed on all sputum specimens from all other inpatient sources during the same 2-wk period were positive. The only exposure factor common to all cases was the use of one or both of the ward showers. Compared with 36 ARW control patients, cases were more likely to report clinical criteria for chronic bronchitis (odds ratio, 6.6; 95% confidence interval, 1.5 to 28.6; p = 0.02). Using phenotype analysis, plasmid profiles, and pulsed-field gel electrophoresis of large genomic DNA restriction enzyme fragments, the 16 case isolates were found to be identical. This strain of M. fortuitum was also cultured from a tap connected to the water line supplying the ARW showers, but not from the showers themselves. No further cases were identified after the showers were disconnected and decontaminated. To our knowledge, this is the first clinical use of pulsed-field gel electrophoresis for genetic comparison of mycobacterial strains. It demonstrates the important potential of this technique for studying the epidemiology of mycobacterial infections. Showers should be considered a possible source of nosocomial respiratory tract colonization with M. fortuitum.