Five Years without Mycobacterium chimaera

Objectives: In July 2014, the Swiss Federal Office of Public Health reported infections caused by Mycobacterium chimaera in patients, that were operated on using heart lung machines with contaminated heating cooling units (HCU). These devices regulate the temperatures of both, the blood and the cardioplegia. The Mycobacterium was detected in water samples of the HCUs as well as in the room air.

Methods: In 2014, a new operative center was built on our campus and as a part of that seven new HCUs 3 T (Sorin GmbH, Germany) were purchased. The cleaning/disinfection units are equipped with water filters to eliminate bacteria Pall-Aquasafe (Pall medical, UK). Despite cleaning/disinfection according to the manufacturer’s instructions Mycobacteria were detectable after a short time. In September 2015 the 2014 HCUs were replaced by new devices (Sorin 3 T). The initial 14-day disinfection of the new HCUs was performed with Puristeril 340 (Fresenius medical care, Germany). The HCUs and the water filters were sampled in a biweekly mode and the room air in the operating theatres was examined on a regular basis.

Results: Prior to commissioning the new HCUs all samples were microbiologically negative. In 2015 (September 2015 to December 2015), twelve samples were obtained from the devices and Pseudomonas aeruginosa was detected once. In 2016, device samples were obtained monthly and Fusarium solari (four times) and Brevundimonas spp. (once) were detected. In 2017, nine samples were analyzed with two positive results (Cupriavidus pauculus and metallidurans, respectively). In 2018, four samples were analyzed with one positive result (Cupriavidus metallidurans). In 2019, three samples were analyzed with two positive results (Cupriavidus metallidurans/necator). From September 2015 to December 2019, all HCU samples and room air tests were negative for Mycobacterium chimaera.

Conclusion: Water management systems are a common problem in health care, especially in surgical facilities. Our results show, that the HCU itself can become contaminated despite maximum efforts. However, using our algorithm, including filters, regular fluid changes, as well as meticulous mycobacterial surveillance so far all tests for Mycobacterium chimaera were negative. Furthermore, daily rotation/circulation of all HCU devices including backup systems may further be an additional strategy to reduce contamination.

No conflict of interest has been declared by the author(s).