Insidious Risk of Severe Mycobacterium chimaera Infection in Cardiac Surgery Patients

<span class="paragraphSection"><div class="boxTitle">Abstract</div><div class="boxTitle">Background.</div>An urgent UK investigation was launched to assess risk of invasive <span style="font-style:italic;">Mycobacterium chimaera</span> infection in cardiothoracic surgery and a possible association with cardiopulmonary bypass heater-cooler units following alerts in Switzerland and The Netherlands.<div class="boxTitle">Methods.</div>Parallel investigations were pursued: (1) identification of cardiopulmonary bypass–associated <span style="font-style:italic;">M. chimaera</span> infection through national laboratory and hospital admissions data linkage; (2) cohort study to assess patient risk; (3) microbiological and aerobiological investigations of heater-coolers <span style="font-style:italic;">in situ</span> and under controlled laboratory conditions; and (4) whole-genome sequencing of clinical and environmental isolates.<div class="boxTitle">Results.</div>Eighteen probable cases of cardiopulmonary bypass–associated <span style="font-style:italic;">M. chimaera</span> infection were identified; all except one occurred in adults. Patients had undergone valve replacement in 11 hospitals between 2007 and 2015, a median of 19 months prior to onset (range, 3 months to 5 years). Risk to patients increased after 2010 from <0.2 to 1.65 per 10000 person-years in 2013, a 9-fold rise for infections within 2 years of surgery (rate ratio, 9.08 [95% CI, 1.81–87.76]). Endocarditis was the most common presentation (n = 11). To date, 9 patients have died. Investigations identified aerosol release through breaches in heater-cooler tanks. <span style="font-style:italic;">Mycobacterium chimaera</span> and other pathogens were recovered from water and air samples. Phylogenetic analysis found close clustering of strains from probable cases.<div class="boxTitle">Conclusions.</div>We identified low but escalating risk of severe <span style="font-style:italic;">M. chimaera</span> infection associated with heater-coolers with cases in a quarter of cardiothoracic centers. Our investigations strengthen etiological evidence for the role of heater-coolers 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.</span>

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