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A recent study by the St. Boniface Hospital Albrechtsen Research Centre suggests the only safe number of times an N95 mask can be re-used after autoclave sterilization, is once.  Initiated early in the Covid-19 pandemic, the team of St. Boniface researchers set out to examine how N95 masks worn by lab workers for up to eight hours, and then re-sterilized, would affect performance and efficacy.  

“The results showed that yes, we can safely re-sterilize the kind of single-use N95 masks typically worn by healthcare workers in order to gain a second use, but not more than that,” said Dr. Mike Czubryt, Principal Investigator at St. Boniface Hospital Research Centre, Professor of Physiology and Pathophysiology at the University of Manitoba and lead author of the paper recently accepted for publication by The Journal of Hospital Infection and available here:

As a research team, Czubryt explained how they wanted to look at what happens when they re-sterilized masks worn by living, breathing human beings in real-life conditions. Will the wearing of a mask and subsequent sterilization attempts, affect the material, the fit and the filtration?  The answers were yes. 

“After a second sterilization cycle, the masks started to fail the fit testing, deeming them unsafe for use in a healthcare setting,” Czubryt said.  While these results are discouraging in light of previous studies that seemed to suggest autoclave and other forms of chemical re-sterilization is possible up to 10 times, the St. Boniface researchers are sharing these results to serve as a caution against multiple re-sterilization attempts. The difference between this work and previous studies is the consideration of real-world use, which significantly degrades masks and limits their reuse.

“Since masks can be re-sterilized once, that will still theoretically double the current stockpile of N95s around the world,” Czubryt said, “So this information should be helpful for healthcare decision-makers who are looking at exactly how far they can stretch their stockpile and how much to order from suppliers for future needs.”

The study’s publication in one of the most accessed medical journals on infection prevention and control means that many other health care teams will benefit from the detailed guidance on how the sterilization process can be rolled out in a large urban hospital setting.  “Our paper describes a workflow for other health care facilities to safely recycle hundreds of masks per day while keeping workers safe,” he shared. Autoclaves are common equipment in many healthcare settings, making the study widely applicable.

“This is one of the greatest takeaways from this study and for St. Boniface Hospital in particular, as we are already stockpiling extra masks,” said Executive Director of Research, Dr. Grant Pierce, also a Principal Investigator and co-author of this study.  Dr. Pierce works closely with St. Boniface Hospital leadership, who were eager for their onsite researchers to explore this idea and how it could help the hospital plan for its own needs during the pandemic.

As Czubryt pointed out, “The team believes that if adopted broadly, our mask re-sterilization protocol could dramatically improve global availability, particularly in areas hardest hit by COVID-19 where supplies are low and new shipments delayed.”

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