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Postoperative M. chimaera infection linked to hospital heater-cooler units
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A 2012 health care-associated outbreak of invasive Mycobacterium chimaera infection in open chest heart surgery patients has been attributed to airborne transmission of the disease from heater-cooler unit tanks, according to recent findings published in Clinical Infectious Diseases.
Researchers from the University of Zurich Hospital launched an investigation after infections with M. chimaera in two heart surgery patients on extracorporeal circulation. The researchers collected water and air samples from operating rooms, ICUs and hospital wards. M. chimaera strains were characterized by randomly amplified polymorphic DNA PCR (RAPD-PCR).
For retrospective case detection, the researchers reviewed all M. chimaera isolates identified by culture since 2006 at the University of Zurich Institute of Medical Microbiology. In addition, the at-risk patient population was prospectively surveyed.
In response to the outbreak, the hospital established an interdisciplinary panel to optimize risk management, and case patients were seen at the hospital on an inpatient or outpatient basis.
The researchers identified six men, aged 49 to 64 years, with prosthetic valve endocarditis or vascular graft infection caused by M. chimaera, which revealed itself clinically after a latency period of 1.5 to 3.6 years postoperatively. The researchers isolated M. chimaera from cardiac tissue specimens, blood cultures or other biopsy samples. Symptoms accompanying infection included fatigue, fever, hepatitis, renal insufficiency, splenomegaly and pancytopenia. The researchers also cultured M. chimaera from water circuits of heater-cooler units connected to the cardiopulmonary bypass, and from air samples taken while the units were operating. No possible common exposures outside the hospital could be identified among the patients. RAPD-PCR showed identical patterns between the M. chimaera strains collected from the heater-cooler unit water and air samples and the strains in two patient clusters.
“Our findings suggest that heater-cooler units should be regarded as a potential source of bacterial infections in cardiac surgery as argued in the past,” the researchers wrote. “In the framework of a Swiss government initiative, several other hospitals have found their heater-cooler units to be growing M. chimaera. In one case, this was linked also to positive air cultures. It remains to be investigated how widespread this risk is for patient safety and what constitutes the most effective measures for its prevention.”
Disclosure: The researchers report no relevant financial disclosures.
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