Emergence of Mycobacterium gordonae in heater-cooler units: a five-year prospective surveillance of devices frequently subjected to chloramine-T booster disinfection.

Background: Worldwide, the detection of Mycobacterium chimaera in LivaNova heater-cooler units (HCUs) has led to their replacement with other HCUs, although non-tuberculous mycobacteria (NTM) have been reported also for HCUs produced by other manufacturers. In almost all hospitals of our region, LivaNova HCUs have been replaced with Maquet HCU40s, regularly disinfected with chloramine-T.

Aim: To report the results of the surveillance over a 63-month operation period of the Maquet devices, and to provide a trend in NTM positivity over time.

Methods: Twenty-nine Maquet devices (HCU40 and HU35) were monitored by two culture methods and propidium monoazide polymerase chain reaction (PMA-PCR) method. The trend in NTM positivity rate was evaluated through the Locally Estimated Scatterplot Smoothing regression and then modelled over time through segmented logistic regression.

Findings: The data acquired during the study period demonstrate a remarkable increase in the positivity rate, especially after the third year (maximum slope change at 1280 days). Non-tuberculous mycobacteria were isolated in 150 water samples (37.2%); 100% and 62% of HCU40 and HU35 devices, respectively, were colonized with non-tuberculous mycobacteria. The most frequently detected species were Mycobacterium gordonae (73%) followed by Mycobacterium chelonae (41%) and Mycobacterium paragordonae (11%).

Conclusion: Preventive strategies by disinfection with chloramine-T did not effectively reduce non-tuberculous mycobacteria colonization of Maquet devices. Although, to date, no cases of postoperative invasive infections linked to Maquet devices have been reported, our microbiological results emphasize the need for (1) designing changes to increase safety of devices and (2) researching and developing new disinfection protocols including alternative molecules.