Bacterial contamination of water used as thermal transfer fluid in fluid-warming devices

Recent reports implicated heater-cooler units (HCUs), which are used for warming infusions, blood or in extracorporeal membrane oxygenation devices, as a possible origin of healthcare-associated infections (HAIs) with potentially pathogenic bacteria, such as non-tuberculous mycobacteria [1]. This represents a source of contamination in a usually sterile setting.

To analyse water from infusion heating devices (IHDs) for bacterial contamination, and to determine if IHDs are a potential source in the transmission of HAIs.

Thermal transfer fluid (TTF; 300-500 mL) was collected from the reservoirs of 22 independent IHDs and processed on different selective and non-selective media for colony count and identification of bacteria. Strains of Mycobacterium spp. were analysed by whole-genome sequencing.

Bacterial growth was observed in all 22 TTF samples after cultivation at 22 °C and 36 °C. Pseudomonas aeruginosa was the most frequent pathogen identified, present in 13.64% (3/22) of samples at >100 colony-forming units/100 mL. Colonization with Mycobacterium chimaera, Ralstonia pickettii and Ralstonia mannitolilytica was detectable in 9.09% (2/22) of samples. Primary sequencing of the detected M. chimaera suggests a close relationship with a M. chimaera strain detected in an outbreak in Switzerland which led to the death of two patients.

Contamination of TTF represents a germ reservoir in a sensitive setting. Handling errors of IHDs may lead to the distribution of opportunistic or facultative bacterial pathogens, increasing the risk of transmission of nosocomial infections.