hcudesignand transmission of
m.chimaera 839
by Marra et al,2 the results of mycobacterial culturing can be highly variable and sensitivity of the method is not known. Nevertheless, the FDA recommends considering micro- biological sampling if contamination is suspected,17 and the Swiss authorities (Federal Office of Public Health and Swiss- Medic) recommend routine sampling.9 Furthermore, we did not perform quantitative sampling that may be important for estimating spread. However, such quantification is not stan- dardized and is difficult to interpret. Finally, we cannot exclude the possibility that no other HCUs than the 3T aero- solizes M. chimaera. It could be argued that it is a statistical phenomenon and that all patients worldwide were con- taminated through the 3T HCU because it is by far the most used type ofHCUworldwide, with ~60% of the market share.2 Nevertheless, this study provides strong evidence that the 3T HCU has the largest propensity to aerosolize M. chimaera due to its machine design. Further studies are needed to exclude M. chimaera aerosolization through other HCUs. To solve the issue of air contamination in the operating
room, several solutions have been proposed. Removing the HCU from the operating room can confer a definite solution. Containing the HCUs in a custom-made housing could also prevent spread of contaminated aerosols. However, knowledge about the main direction of airflow of the HCU is essential to optimizing each solution or, if the HCUs stay unprotected in the OR, to position them with the airflow directed away of the patient. Manufacturers should optimize the design of the HCUs so that aerosol production is minimized and produced aerosols are not expelled and do not come in contact with the ventilator air stream. Not only M. chimaera but also other mycobacteria or water-
living microorganisms can colonize HCUs12,18 and may the- oretically lead to transmission to patients. Therefore, it will be worthwhile to develop materials with reduced potential for colonization. Regular exchange of the tubes can further minimize the risk for colonization. Concerning maintenance, all manufacturers have intensified the disinfection protocols and intervals. However, the recommended weekly disinfec- tion, as for the HCU40, may lead to rapid attrition of the materials and generates relevant economic costs through increased workload. The optimal disinfection interval without increasing the risk for the patients still needs to be determined. In conclusion, we believe that we have identified key issues in
the design of HCUs that could explain the higher risk of dis- persal by the 3T HCU. Especially the close contact of a strong ventilator to the aerosol-leaking water tank may be an impor- tant factor for aerosolization of M. chimaera in the 3T HCU. Also, the HCU40 differed in 4 major aspects of its design, and it showed continuous negative results during microbiological surveillance over 15 months of operation. Currently, many authorities recommend placing HCUs outside the OR. How- ever, based on our study, such improved devices may remain in the OR during cardiac procedures. These results offer a starting point from which to design a new safer device to ensure the safety of patients undergoing cardiac surgery.
acknowledgments
Financial support: This study was funded without restriction by the University Hospital of Basel. Maquet GmbH provided an unrestricted grant to partly cover the microbiological analyses. Maquet GmbH did not have any access or influence on study design, data analysis, or manuscript writing. Potential conflicts of interest. All authors declare no conflicts of interest.
Address correspondence to Prof Dr Andreas F. Widmer, MD, MS, Division
of Infectious Diseases and Hospital Epidemiology, University Hospital Basel, Petersgraben 4, 4031 Basel, Switzerland (
andreas.widmer@usb.ch).
supplementary material
To view supplementary material for this article, please visit
https://doi.org/10.1017/ice.2018.102.
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