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Study: More Than One-third of Surgical Heater-Cooler Units Showed Contamination

Safety concerns are being raised once again about heater-cooler units (HCUs), which control the temperature of a patient's blood and organs during heart bypass surgery.

The FDA and CDC previously issued safety warnings about the risk that a popular brand of HCU could be contaminated during manufacturing, heightening the risk of dangerous patient infections, according to a presentation at the recent 44th Annual Conference of the Association for Professionals in Infection Control and Epidemiology (APIC) in Portland, OR.

In fact, the study notes that about 60% of heart bypass procedures performed in the United States employ that brand of heater-cooler unit.

The presentation by the Pittsburgh-based Special Pathogens Laboratory found in recent research that 33 out of 89 HCUs assessed between July 2015 and December 2016 tested positive for Mycobacterium chimaera (M. chimaera). The bacterium has been linked to fatal infections in open-heart surgery patients, but it has been unclear to what extent colonization of M. chimaera might be present in the units.

The devices in the study already were in use when the researchers tested them for the presence of nontuberculous mycobacteria (NTM) colonization — primarily M. chimaera — in HCUs before and after decontamination. Overall, 653 water samples from 89 units were evaluated.

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The samples came from 23 hospitals in 14 states, the District of Columbia, and Canada. In addition to the 37% that tested positive for M. chimaera, four units were found to be colonized with Legionella. Many other strains of mycobacteria were found in additional HCUs, according to the presentation.

Researchers said they were shocked at the level of contamination in the units; 97 cultures were considered uninterpretable because of high levels of bacterial and fungal contamination.

"The extent of contamination from such a rare organism in multiple units from all over the country was surprising," said John Rihs, vice president of laboratory services at Special Pathogens Laboratory. "Some devices remained positive for M. chimaera for months, indicating that disinfection can be difficult and routine testing is advisable. Beyond M. chimaera, we found other NTM species, Legionella, and fungi, indicating these units are capable of supporting a diverse microbial population."

Study authors recommend that hospitals create and oversee regular cleaning, disinfection, and maintenance schedules for heater-cooler devices to minimize the risk of NTM colonization. They also urge monitoring for fungi, Legionella, and overall contamination that can be spread to the patient if water from HCUs becomes aerosolized.

Patients exposed to M. chimaera, which is often found in soil and water but usually is not associated with infections, during open-heart surgery can develop general and nonspecific symptoms that often can take months to emerge. Based on CDC and FDA instructions, hospitals must notify patients who have had open-heart surgery within the last five years that they were potentially at risk for infection.