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Researchers advise hospitals on locating, preventing M. chimaera cases linked to HCDs
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Researchers advised hospitals on how to locate and notify patients who may have been exposed to Mycobacterium chimaera from contaminated LivaNova 3T heater-cooler devices during cardiac surgery.
Dan Diekema, MD, clinical professor and associate hospital epidemiologist at the University of Iowa Hospitals and Clinics, and colleagues also advised hospitals to separate their LivaNova 3T devices from the operative field due to the risk of invasive infections caused by aerosolized M. chimaera.
LivaNova 3Ts have been linked to a global outbreak of difficult-to-diagnose M. chimaera infections, leading to warnings about their safety. Researchers believe the devices, which are used with heart-lung machines to regulate body temperature during cardiothoracic surgeries and other medical procedures, were most likely contaminated at the German plant where they are manufactured.
Diekema and colleagues said all LivaNova 3Ts should be considered contaminated regardless of when they were manufactured or whether they have tested negative for M. chimaera. Accordingly, they said any patient who underwent surgery while one of the devices was running in the OR at least as far back as 2010 should be considered exposed to M. chimaera and at risk of developing an infection.
“The No. 1 thing for clinicians to know is that they should keep M. chimaera in mind for patients with a compatible clinical syndrome who have had cardiopulmonary bypass in the past 4 to 6 years because the symptoms are delayed, can be vague and diagnosis can only be made with specialized lab testing,” Diekema told Infectious Disease News.
Devices used widely
M. chimaera is a slow-growing species of nontuberculous mycobacteria (NTM) commonly found in soil and water that rarely makes people sick, according to the CDC. Symptoms including fatigue, fever, sweats, dyspnea, weight loss and cough are often delayed and difficult to distinguish from other infections, making it hard to find cases, Diekema and colleagues said.
Patients can be infected through M. chimaera-containing bioaerosols that are produced by LivaNova 3Ts during surgery. According to Diekema and colleagues, the most serious infections have involved prosthetic valves, vascular grafts and left ventricular assist devices and all have followed surgical procedures that involved cardiopulmonary bypass. They said other heater-cooler devices (HCDs) have tested positive for M. chimaera, but none have been linked to the outbreak.
According to a CDC estimate, in hospitals that have identified at least one HCD–related infection, the risk of a patient being infected with M. chimaera is between approximately one in 100 to one in 1,000. Despite the risk, Diekema told Infectious Disease News that hospitals continue to use LivaNova 3Ts because the devices make up 60% to 80% of the global market for HCDs and there is not a sufficient supply of other brands to meet the demand. (The CDC estimates that LivaNova 3Ts are used in 200,000 surgeries per year in the U.S.)
“Surgery would have to be halted at many institutions, which would also cost lives if timely cardiac surgery were not available,” Diekema said. “So until an engineering solution is devised that absolutely [ensures] that HCDs won't produce bioaerosols, centers are using a variety of temporizing measures to separate HCD exhaust air from OR air, particularly for the LivaNova 3T units.”
Notifying patients
Diekema and colleagues said any symptomatic patients exposed to a LivaNova 3T since 2006 — the year hospitals began using the devices — should have M. chimaera in their differential diagnosis. They recommended several steps to identify, notify and test potentially infected patients, beginning with developing a list of exposed patients.
Most infected patients have developed symptoms within 4 years of surgery, leading the CDC to recommend going back that far to identify potential cases. However, Diekema and colleagues said going back 6 years — the longest time between exposure and clinical symptoms in any patient so far — is more conservative, and checking patients all the way back to 2006 is the most comprehensive method of case finding.
Once a list of exposed patients is made, Diekema and colleagues said hospitals should contact each one individually via closed-loop communication; for instance, by sending patients a letter explaining the situation and asking them to call the hospital for a telephonic symptom screen, after which patients who report symptoms can be further evaluated. At the same time, hospitals should send news releases to local media outlets, create a webpage with resources for patients and medical professionals and notify local clinicians about the issue, Diekema and colleagues said.
They said patients who do not respond should be contacted by other means.
The list of exposed patients should also be compared with Mycobacterium-positive laboratory cultures that have been identified after looking back through the records, and with patients who have been diagnosed with sarcoidosis, because it can be confused with M. chimaera infection, Diekema and colleagues said.
Finally, Diekema and colleagues said an EMR alert can be developed to notify clinicians — and possibly local hospital epidemiologists or infectious disease physicians — when a potentially exposed patient develops symptoms that could indicate an M. chimaera infection.
They said exposed patients with symptoms of M. chimaera infection should be evaluated using two or three mycobacterial blood cultures. “If those are negative,” they wrote, “consideration should be given to culture and histopathology of bone marrow and other affected organs or body sites, and additional blood cultures should be performed in 1-2 months.” They warned that cultures could take 2 to 8 weeks to turn positive because M. chimaera grows slowly, and speciation may take even longer.
‘Perfect storm’
NTM, including M. chimaera, are at least 1,000 times more resistant to disinfectants than Escherichia coli, making HCDs difficult to decontaminate. In line with other guidance, Diekema and colleagues said the best way to keep patients away from potentially contaminated HCDs is to remove the devices entirely from the OR. (At the University of Iowa, for example, Diekema and colleagues said the HCD is stationed outside the OR and is operated remotely by a perfusionist, with the device’s hoses passed through a small portal in the OR wall that is covered by a sliding door.)
Where removing the HCD is not feasible, hospitals could instead build housing for their devices in the OR with a separate exhaust system to keep potentially contaminated air from patients, Diekema and colleagues said. They also described an unproven method of positioning the HCD so that its exhaust is directed away from patients.
“Point source contamination of HCDs with M. chimaera represents a ‘perfect storm’ for a slowly developing, difficult-to-detect global outbreak,” Diekema and colleagues wrote. “Consequently, many patients are at risk for M. chimaera infection due to exposure to bioaerosols produced by HCDs used globally in cardiothoracic surgery.
“There is currently no evidence to define a lower threshold of mycobacterial contamination in air or water samples for preventing M. chimaera infection. Thus, the most important control measure currently is to remove HCDs from the OR until new HCD designs are available that prevent bioaerosol production.” – by Gerard Gallagher
Reference:
Marra AR, et al. Clin Infect Dis. 2017;doi:10.1093/cid/cix368.
Disclosure: The researchers report no relevant financial disclosures.