Aerosolization of Mycobacterium chelonae from heater-cooler-devices: a continuing risk of exposure during cardiac surgery.

Background: Following identification of widespread Mycobacterium chimaera infections in 2013 associated with aerosolization from Sorin heater-cooler-devices (HCD), microbiological monitoring of HCDs has become mandatory in Switzerland.

Methods: Since 01/2016, four Maquet HCU40 (Getinge) HCDs have been in operation at the University Hospital Basel. Monthly water cultures for Gram-negative bacteria and mycobacteria were performed, including samples from two filling lines equipped with 0.2 μm water filters. Intermittent monthly air sampling for mycobacteria was conducted.

Results: Between 01/2016 and 05/2018, various non-fermenting bacteria were cultured. Mycobacterium chelonae was first isolated in 06/2018 from HCD water tanks. Mycobacteria cultures from the filling lines remained negative. The first air sample positive for M. chelonae was collected in 12/2019. Despite intensified disinfection measures from 01/2022 onwards, M. chelonae could be cultured in air samples, collected at 30 cm and 120 cm height adjacent to three of the four running HCDs in 07/2022. Whole genome sequencing identified a cluster of isolates differing by a maximum of four single nucleotide polymorphisms. Despite extensive investigations, the source of M. chelonae remains undetermined. To date, no infections with M. chelonae have been related to the contaminated HCDs at our institution.

Conclusions: Our data confirms the risk of aerosolization of non-tuberculous mycobacteria from HCDs, irrespective of HCD-design and manufacturer. These findings underscore the importance of routine microbiological surveillance, including both water and air sampling when HCDs are placed within the operation room to prevent exposure of the operating field to the air exhausts of HCDs.