Mycobacterium chimaera has been identified in recent years as a closely related strain of Mycobacterium avium complex. However, little is known about cases of outbreak due to Mycobacterium chimaera in hospitals to date. Jan. 2014-Jun. 2014, we noticed an increased incidence of non-tuberculous mycobacteria in sputum cultures from hematological patients undergoing stem cell transplantation (SCT). Mycobacterium (initially identified as M. intracellulare) were isolated from ten sputum samples with eight patients over this period, compared with 2-3 cases during the year before. We focused our investigation on water sources in the ward.
Methods: Water samples were obtained from shared tea supplier, clean water hand-washing machines in each patient rooms which generates sterile water by UV lamp through filtration. Variable number of tandem repeats (VNTR) typing was done to distinguish genetically among strains of Mycobacterium.
Results: PCR and culture for M.intracellulare were positive in 13 of 28, 17 of 28 rooms of SCT center respectively, negative in tea supply machine. None of the patients was symptomatic, then this phenomenon was seemed to be pseudo-outbreak. Cultures for general bacteria, fungi were negative. The culture and PCR of the water from upstream water supply system was negative. Water stain were observed in the outlet mouth of sterile water hand-washing machines in each rooms. Mycobacteria were isolated from water stain in the drain trap of the faucet. VNTR typing analysis revealed 4 strains out of 8 samples from patients’ sputum, and 13 out of 20 samples from sterile warm water hand-washing machines were genetically identical; Mycobacterium chimaera. The plates in water spout distant from UV lamp were not replaced over five years, and patients frequently used it for mouth wash or drinking. After replacement of water stained plate at outlet mouth of sterile water hand-washing machines, it is not detected even once for two years.
The pseudo-outbreak of Mycobacterium chimaera in our SCT center was likely due to water stain of faucet of sterile water supply machine. In SCT unit, sterile water machine was widely used, however, we should take regular maintenance and exchange of faucet parts into consideration in the sterile water hand-washing system to prevent biofilm formation by non-tuberculous Mycobacterium.