The link between M. chimaera and heater cooler units grows stronger

A new paper in the Journal of Hospital Infection from Germany confirms the work of Hugo Sax and colleagues in Switzerland on the aerosolization of M. chimaera by heater cooler units. These investigators cultured M. chimaera from the water tanks of 4 Sorin heater cooler units, and were able to culture the organism from the air in the operating room only when the units were turned on. They were also able to culture non-fermenters from the air up to 10 feet from the heater cooler units when the units were turned on, but not when they were turned off. Importantly, the investigators were not able to culture M. chimaera from the hospital's water supply. And the authors note that whole genome sequencing of clinical and environmental isolates from the Netherlands and Germany suggests the possibility that the heater cooler units are intrinsically contaminated (i.e., this is a point source outbreak).

Lastly, the authors state that "only strict separation of the heater cooler unit from the operating room appears to enhance patient safety." We agree and that is the mitigation strategy that we have used at the University of Iowa. Below are photographs of our engineers' solution, a 6 x 6 inch Corian portal through the wall of the operating room, so that the heater cooler units are housed outside of the OR. The door is light weight and closes fully when the heater cooler device is not needed, and partially when the heater cooler hoses are extending through the wall. Positive pressure in the OR is maintained when the portal is in use.

Dan and I have spoken with a number of physicians from across the country, and we are now aware of 18 M. chimaera infections in patients who have undergone cardiopulmonary bypass. All of these patients, with the possible exception of 1 patient, had a prosthetic valve or vascular implant placed. So patients with implants are most important if a look back needs to be performed for case finding.