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BACKGROUND: An urgent UK investigation was launched to assess risk of invasive Mycobacterium chimaera infection in cardiothoracic surgery and a possible association with cardiopulmonary bypass heater-cooler units following alerts in Switzerland and the Netherlands. METHODS: Parallel investigations were pursued: i) identification of cardiopulmonary bypass-associated M. chimaera infection through national laboratory and hospital admissions data linkage ii) cohort study to assess patient risk iii) microbiological and aerobiological investigations of heater-coolers in situ and under controlled laboratory conditions iv) whole genome sequencing of clinical and environmental isolates. RESULTS: Eighteen probable cases of cardiopulmonary bypass-associated M. chimaera infection were identified, all except one adults. Cases had undergone valve replacement in 11 hospitals between 2007-2015, a median 19 months prior to onset (range 3 months-5 years). Risk to patients increased after 2010 from <0.2 to 1.65/10,000 person-years in 2013, a nine-fold rise for infections within 2y of surgery (RR=9.08, 95% CI 1.81-87.76). Endocarditis was the most common presentation (n=11). To date, 9 cases have died. Investigations identified aerosol release through breaches in heater-cooler tanks. M. chimaera and other pathogens were recovered from water and air samples. Phylogenetic analysis found close clustering of strains from probable cases. CONCLUSIONS: We identified low but escalating risk of severe M. chimaera infection associated with heater-coolers with cases in a quarter of cardiothoracic centres. Our investigations strengthen aetiological evidence for heater-coolers' role in transmission and raise the possibility of an ongoing, international point-source outbreak. Active management of heater-coolers and heightened clinical awareness are imperative given the consequences of infection.

Original publication




Journal article


Clin Infect Dis

Publication Date



Aerosol Release, Cardiac Surgical Procedures., Disease Outbreaks, Equipment Contamination, Nontuberculous Mycobacteria