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

Abstract

Objective: To evaluate an unusual number of rapidly growing acid-fast bacilli, later identified as Mycobacterium chelonae, and pink bacteria, later identified as Methylobacterium mesophilicum, from fungal cultures obtained by bronchoscopy.

Design: Outbreak investigation.

Setting: An academic medical center performing approximately 500 bronchoscopies and 4,000 gastrointestinal endoscopies in 1998.

Patients: Patients undergoing bronchoscopy July 21 to October 2, 1998.

Methods: 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 DNA fingerprinting.

Results: 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. The above sources remained positive for the same organisms after a glutaraldehyde cleaning cycle of the automated washers. DNA finger-printing of the M. chelonae revealed that they were clonally related.

Conclusions: The automated washers were contaminated with a biofilm that rendered them resistant to decontamination. The washers then contaminated the endoscopes and bronchoscopes they were used to disinfect. Our institution purchased new endoscopes and a new paracetic acid sterilization system.