Since 2013, over 100 cases of Mycobacterium chimaera prosthetic valve endocarditis and disseminated disease were detected in Europe and the United States, and these were presumptively linked to contaminated heater-cooler units (HCUs) used during cardiac surgery. A molecular epidemiological analysis of microbial isolate genomes detected a “remarkable clonality of isolates” in almost all of the assessed patients with M. chimaera disease, which “strongly points to a common source of infection,” as reported online in The Lancet Infectious Diseases.
The analysis comprised 250 whole-genome sequencing datasets: 24 isolates from 21 cardiac surgery–related patients in Switzerland, Germany, the Netherlands, and the United Kingdom; 36 from 35 unrelated patients; 126 from LivaNova HCUs in use (85 water cultures, 41 air cultures); 13 from LivaNova HCUs returned to the production site in Germany for disinfection; 4 from the LivaNova production site (3 from newly produced HCUs, 1 from a water source); 2 from Maquet extracorporeal membrane oxygenation (ECMO) devices in use; 14 from Maquet HCUs in use; 15 from new Maquet HCUs sampled at the production site; and 7 from hospital water supplies in Switzerland, Germany, and the Netherlands, plus one M. chimaera DSM 44623–type strain, and eight M. intracellulare strains (from four unrelated patients from Germany and four published genomes).
Isolates were analyzed by next-generation whole-genome sequencing and compared with published M. chimaera genomes, according to Jakko van Ingen, PhD, Radboud University Medical Center, Nijmegen, the Netherlands, and his colleagues. Phylogenetic analysis of these 250 isolates revealed two major M. chimaera groups. They found that all cardiac surgery–related patient isolates could be classified into group 1. They then did a subgroup analysis.
“Three distinct strains of M. chimaera appear to have contaminated the water systems of LivaNova HCUs at the production site, belonging to subgroups 1.1, 1.8, and 2.1,” the authors stated. However, most M. chimaera isolates from air samples taken near operating LivaNova HCUs and those of 23 of the 24 related patients belonged to subgroup 1.1.
“This finding further supports the presumed airborne transmission pathway leading to endocarditis, aortic graft infection, disseminated disease, and surgical site infections in the affected patients,” according to the authors (doi: 10.1016/S1473-3099[17]30324-9).
The results suggest “the possibility that the vast majority of cases of cardiothoracic surgery–related severe M. chimaera infections diagnosed in Switzerland, Germany, the Netherlands, the United Kingdom, the United States, and Australia resulted from a single common source of infection: LivaNova HCUs that were most likely contaminated during production in Germany,” the researchers concluded.
The study was partly funded by the EU Horizon 2020 program, its FP7 program, the German Center for Infection Research (DZIF), the Swiss National Science Foundation, the Swiss Federal Office of Public Health, and National Institute of Health Research Oxford Health Protection Research Units on Healthcare Associated Infection and Antimicrobial Resistance. The authors reported having no relevant conflicts.