Contaminated heater-cooler units produced in Germany have been identified as the likely source of a Mycobacterium chimaera infection that affected 21 open-heart surgery patients across Europe, USA and Australia.
In the first investigation to use whole genome sequencing, a study published in The Lancet Infectious Diseases found that the units produced by LivaNova were most likely to be the cause.
However, the authors say hospital water systems and another brand of heater-cooler units, Maquet, were also found to be contaminated during production and use, which means the infection risk might persist despite controlling contamination at the LivaNova production line.
Infection with M. chimaera bacteria during open-heart surgery can cause prosthetic valve endocarditis and spread to the rest of the body. Since 2013, more than 100 cases of M. chimaera infection have been reported in the EU, the USA, and Australia, while many countries have issued guidance to reduce the risk of infection.
Although previous studies have suggested a link to contaminated heater-cooler units used during open-heart surgery, until now there has been no firm evidence linking the outbreak to a source.
The new study analysed the DNA from 250 M. chimaera samples, which included samples from 21 open-heart surgery patients in Switzerland, Germany, the Netherlands, and the UK, and samples collected from LivaNova and Maquet heater-cooler units, other water-containing medical devices, tap water, and drinking water dispensers in hospitals. LivaNova and Maquet contributed samples from their production sites.
It also included samples from patients with M. chimaera from Switzerland, Germany, the Netherlands and the UK who had not undergone open-heart surgery.
The authors of the report say because the samples from most of the open-heart surgery patients were so similar, a common source of infection was likely and after investigation concluded that LivaNova heater-cooler units were the common source of infection and that contamination occurred during production.
The researchers compared their findings to publically available datasets containing samples from open-heart surgery patients from the US and Australia, and matched a further 12 patients to the LivaNova production site.
Co-author Professor Stefan Niemann, of the National Centre for Mycobacteria, Forschungszentrum Borstel, Germany, said: "Molecular epidemiological investigation by applying whole genome sequencing is the most powerful tool for tracing pathogen transmission. Our study closes the missing gap and provides evidence that the international health-care related M. chimaera outbreak can most likely be attributed to a point source."
Co-author Professor Dr Hugo Sax, of University Hospital Zurich, Switzerland, added: "Local contamination of heater-cooler units with M chimaera also occurred and at least one patient could have been infected through this route. Operating rooms and other hospital settings with patients at increased risk of infection should be devoid of such uncontrolled water sources."
Sax H et al. Global outbreak of severe Mycobacterium chimaera disease after cardiac surgery: a molecular epidemiological study. The Lancet Infectious Diseases. 13 July 2017; doi: 10.1016/S1473-3099(17)30324-9 [abstract]
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