To the Editor: The interesting and timely paper by Cain et al.1, in press in the Journal of Cardiac Surgery , provides important details concerning the devastating consequences of Mycobacterium chimaera (MC ) infection. In their patient extreme fragility of the mediastinal tissues was observed after repair of an acute aortic dissection; during follow-up multiple reoperations were required to treat recurrent dehiscence of the aortic grafts. Despite repeat explantation of foreign materials infection persisted with mediastinitis and eventual systemic diffusion with fatal outcome.MC infection after open cardiac surgery using cardiopulmonary bypass has been recently reported as a clinical outbreak worldwide and identified as originating by contaminated water in heater-cooler units2. Current experience shows that MC causes a slow-growing and extremely difficult to treat infection with an incubation period which has been recently demonstrated to be as long as >12 years3.We have recently treated a patient, quite similar to that reported by Cain et al.1, who presented with a pseudoaneurysm of the distal suture line twelve years after repair of type A aortic dissection4. At first operation replacement of the ascending aorta and hemiarch using of a Djumbodis®dissection system (Saint Come-Chirurgie, Marseille, France) was performed. At reoperation extremely fragile tissues were noted and, after removing the metallic stent, the aortic arch was replaced with a frozen elephant trunk technique. Cultures of the excised material grewMC . In this case we hypothesized that the stent played an important role in the onset of infection for at least 2 reasons: presence of foreign material in the blood stream and injury to the aortic wall by the edges of the stent. The case described by Cain et al.1 also supports our belief that extreme fragility of the aortic tissues caused by MB was a further important factor in the occurrence of this complication.Interestingly, a delayed diagnosis occurred in both cases; this most likely played a critical role in favouring development of extra‐cardiac manifestations of the disease, in reducing the effectiveness of antibiotic therapy due to immunologic impairment and causing a negative outcome in both patients.MB infection may have different locations ranging from single-organ to systemic manifestations5. When it involves the mediastinum and particularly the major vascular structures often results in life-threatening complications despite proper antimycobacterial treatment. An early diagnosis, even with significantly extended surveillance, appears extremely difficult due to slow-growing and long incubation period of MB .Although no specific guidelines are so far available, intra-operative prevention with improvement of setting and development of heater-cooler units is mandatory and should be based on specific recommendations5.
