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This award-winning blog supplements the articles in Hospital Infection Control & Prevention.

Heater-Cooler Units Commonly Used in Heart Bypass Surgery Linked to Fatal Infections

By Gary Evans, AHC Media Senior Staff Writer

An “insidious” under-the-radar outbreak of water-borne bacteria aerosolized by heater-cooler devices commonly used in cardiothoracic surgery is emerging as a clear and present danger to patient safety, a veteran epidemiologist warned a meeting of infectious disease physicians Friday in Atlanta.

“I use the term insidious to describe this illness in terms of its very delayed onset of symptoms from the time of surgery and the very delayed time [from symptoms] to diagnosis,” Dan Diekema, MD, chief of infectious diseases at the University of Iowa said a May 20 meeting of the Society for Healthcare Epidemiology of America (SHEA). “ “I think this is probably the most challenging problem I have been presented as a hospital epidemiologist.”

Infections involving a heretofore obscure bacterium named Mycobacterium chimaera – ubiquitous in soil and water but rarely pathogenic – are being reported in the United States and Europe. The common link is heating-cooling devices used in open heart bypass and other surgeries that can serve as a water reservoir for the pathogen and aerosolize it into the operating field. Heater-cooler devices are often used during cardiac surgical procedures to warm and cool a patient’s blood during cardiopulmonary bypass. The units have a closed circuit system to circulate water, but can create an aerosol that is vented into the immediate environs by an exhaust fan.

The problem – and there are many – is that the M. chimaera is exceedingly difficult to detect, treat, and eradicate from devices, shrugging off both antibiotics in humans and powerful disinfectants in machines. It subsequently emerges in post-surgical patients as a slow growing but potentially fatal infection that may not become symptomatic for a year or more. Though there have been only an estimated 65 to 70 documented cases in the U.S. and Europe, it is a given that many more cases are likely being missed because of the difficulty in detecting infections that appear far removed from the surgical exposure.

“The case-finding is very problematic with many patients receiving cardiopulmonary bypass away from home and all their follow-up care is local,” Diekema said. “The symptoms are very non-specific -- they present months to years after the exposure. And exposure [during] cardiothoracic bypass has not normally – to this point – been considered a risk for this clinical syndrome. The risk mitigation issue is difficult as well and I think we don’t know yet if these units can be decontaminated.”

Mortality over 50%

The University of Iowa alerted some 1500 surgical patients to seek evaluation after becoming aware in January that a patient who had an aortic valve replacement in 2012 had developed M. chimera infection that was not responding to treatment. Two other infected cardiac surgical patients have been identified as Diekema and colleagues continue the look-back effort.

“Most disturbing is the crude mortality [in all cases] is well over 50%,” he said. “The story is not over yet – there are a lot of patients who are struggling with this and not doing well.”

Treatment is particularly difficult if the bacteria establish biofilms on prosthetic valves or other implanted materials to assist cardiothoracic function. Diekema underscored this point with a slide of a micro-valve ring removed from a patient in Europe still heavily contaminated with a biofilm despite a year of multidrug therapy.

“We have had similar experiences,” he said. “Our index case, who died just last weekend, had continuous mycobacteremia for well over a year despite multiple drug therapy. [There is] just an inability to eradicate this organism in the presence of prosthetic material.”

In a joint alert issued last year, the Centers for Disease Control and Prevention and the Food and Drug Administration called for only sterile water to be used in heater-cooler units. However, there are now questions whether that is enough to prevent infections because it is very difficult to disinfect the units after use no matter what quality of water is used.

“In my view it is very unlikely that [the units] can be decontaminated,” Diekema said. “The experience by people to date has not been very encouraging. After most of the decontamination attempts, ultimately you can regrow the same organism from the unit. This is just my view – not the CDC’s, FDA’s or anyone else’s necessarily – these units cannot be operated safely unless the air coming out of the exhaust is physically separated from the operating room.”

That’s exactly what the University of Iowa did after discovering the M. Chimera cases, having hospital engineers place the unit behind a wall so that the exhausted air cannot reach the operating field. As concern grows about the infections, public health agencies are accelerating efforts to identify the scope of the problem and raise awareness among clinicians. The FDA has called for an expert advisory committee meeting on the heating-cooling devices June 2-3. The CDC also recently posted guidelines to help identify suspect cases.