Secondary Logo

Journal Logo

Pseudo-outbreak of Mycobacterium chelonae and Methylobacterium mesophilicum caused by contamination of an automated endoscopy washer.

Prakash, Udaya B. S. M.D.


Mayo Medical Center and Mayo Medical School, Rochester, Minnesota, U.S.A.

Pseudo-outbreak of Mycobacterium chelonae and Methylobacterium mesophilicum caused by contamination of an automated endoscopy washer.

Infect Control Hosp Epidemiol 2001;22:414–8. Kressel AB, Kidd F. Department of Internal Medicine, University of Cincinnati, Ohio, U.S.A.

Back to Top | Article Outline


This outbreak investigation reports on the results of a study of an outbreak of pseudoinfection by an unusual number of rapidly growing acid-fast bacilli, identified later as Mycobacterium chelonae and Methylobacterium mesophilicum, from fungal cultures obtained by bronchoscopy. The infection control department reviewed patient charts and bronchoscopy logs; obtained cultures of source water, faucets, washers, unopened glutaraldehyde, glutaraldehyde from the washers, and endoscopes; observed endoscope and bronchoscope cleaning and disinfecting procedures; reviewed glutaraldehyde monitoring records; and sent M. chelonae isolates for deoxyribonucleic acid fingerprinting. In 1998, the medical center performed approximately 500 bronchoscopies. During the investigation period (July 21–October 2, 1998), 26 of 131 fungal cultures (20%) obtained by bronchoscopy grew M. chelonae. These 26 cultures came from 22 patients, none of whom had clinical evidence of pulmonary mycobacterial infection. Deoxyribonucleic acid fingerprinting of M. chelonae revealed that they were related clonally. M. chelonae, M. mesophilicum, Gram-negative bacteria, and various molds grew from endoscopes, automated washers, and glutaraldehyde from the washers but not from unopened glutaraldehyde. The endoscopy unit regularly monitored the pH of glutaraldehyde, and the logs contained no deficiencies. These sources remained positive for the same organisms after a glutaraldehyde cleaning cycle of the automated washers. The authors conclude that the automated washers were contaminated with a biofilm that rendered them resistant to decontamination, and as a result, the washers then contaminated the endoscopes and bronchoscopes they were used to disinfect. The medical center purchased new endoscopes and a new peracetic acid sterilization system. The investigators were unable to determine the original source of contamination. The possible causes of contamination included inability to flush the bronchoscopes adequately with 70% alcohol and lack of routine disinfection cycles. The readers are referred to the following publication, which also addresses the problem of a pseudo-outbreak of infection through the bronchoscope.

© 2002 Lippincott Williams & Wilkins, Inc.