A cheap, commonly used method for sterilizing medical equipment may allow hospitals to disinfect and reuse disposable respirator masks, Winnipeg researchers have found, as hospitals hang onto used protective gear amid dwindling supplies.
A research team, led by the University of Manitoba, found certain types of N95 respirator masks can withstand multiple cycles of autoclaving, a technique that, similar to pressure-cooking, involves heat, pressure and steam, and is already widely used for sterilizing instruments in hospitals and clinics. Although these respirator masks are meant to be discarded after each use, the researchers found some models retained their structure and function, even after they went through an autoclave machine 10 times.
“Autoclaves … are essentially available in every medical institution, hospital and large clinic in the world,” said corresponding author Anand Kumar, an intensive-care physician and professor in the departments of medicine, medical microbiology and pharmacology at the University of Manitoba. “If you want a technology [to reprocess masks] that most of the world can use, including very under-resourced places, this is a very good technology for that.”
In a press briefing earlier this week, Canada’s Chief Public Health Officer Dr. Theresa Tam said hospitals should not throw away used face masks and other protective equipment, as public health officials are investigating ways of decontaminating them for reuse. N95 respirator masks became a particular flashpoint recently, when the United States ordered the American-based 3M to stop exporting them to Canada. The U.S. administration has since made a deal with the company to allow it to continue sending the respirator masks, 3M said.
In a statement, Health Canada said that due to the potential critical shortages of personal protective equipment, it “is urgently assessing the evidence to support various decontamination and sterilization methods that would allow the safe and effective reuse of single-use N95 masks.”
Several hospitals said they are not currently reusing respirator masks.
“I think that if our supply chain opens up, then that idea would probably be put aside,” said Dr. Nicola Mercer, medical officer of health for Ontario’s Wellington-Dufferin-Guelph Public Health. “But if we needed to use this [used gear], all creative options are on the table to ensure that our health-care providers have what they need to safely do their job.”
N95 respirator masks are designed to prevent the transfer of airborne particles, fluids and micro-organisms; loose-fitting surgical masks do not protect the wearer in such ways.
In a preliminary manuscript that has yet to be peer-reviewed, Dr. Kumar and his team reported their results from testing four different decontamination methods on various types of N95 respirator masks. Cup-shaped N95 respirator masks, which are made of a material that feels similar to cardboard, did not hold up to autoclaving, Dr. Kumar said. However, autoclaving did work on the types of pleated respirator masks that are made of layered fabric and lie flat.
The researchers also tested the use of ethylene oxide gassing, ionized hydrogen peroxide fogging, and vaporized hydrogen peroxide – methods that use chemicals to denature pathogens.
The researchers found all methods were effective for inactivating the new coronavirus, and the respirator masks were able to withstand at least one cycle of decontamination for each method. But each also had its shortcomings. Ethylene oxide is potentially carcinogenic, and thus, it requires equipment to be aired out for a long period after treatment, Dr. Kumar said. Although the respirator masks stood up quite well to ethylene oxide gassing, an old technique once commonly used for sterilizing scalpels and other medical equipment, Dr. Kumar said he could not recommend this method, in part, because the team could not test for residue.
“It’s one thing to handle an instrument that might have extremely trace amounts of this [chemical residue], it’s another thing to put it on your face and breathe through it,” he said.
Ionized hydrogen peroxide fogging is used in almost every hospital in North America, he said, and the chemical breaks down into harmless water and oxygen. However, the team found the respirator masks became severely damaged and unusable after one cycle of treatment.
Dr. Kumar explained that N95 respirator masks are not simply mechanical filters; some of the internal fibres have an electrostatic charge to trap pathogens. He suggests it is possible that the ionization of this type of hydrogen peroxide treatment may cause damage to the masks.
Vapourized hydrogen peroxide appeared to be most effective; the respirator masks worked well after at least 10 cycles of treatment. However, the technology for this method is not available at most hospitals. Dr. Kumar said industries that use this technology include drug manufacturing, advanced electronics manufacturing and some national and provincial laboratories.
Based on this research, conducted with the National Microbiology Laboratory, some hospitals, such as Toronto’s Sunnybrook Health Sciences Centre, are starting to collect and sterilize used N95 respirator masks using some of these techniques. In the meantime, the hospital says, it is gathering as much evidence as possible to ensure reprocessed respirator masks would be safe to use, if needed.
The Manitoba team is not the only one testing various methods for sterilizing and reusing respirator masks. For instance, Nordion, a supplier of medical isotopes, said it is working with its sister companies Sterigenics and Nelson Labs, owned by Sotera Health, to evaluate ways of resterilizing personal protective equipment amid the pandemic.
The company said the group is working with Canadian government officials, including from the Public Health Agency of Canada and Health Canada, to test the use of various sterilization methods, including gamma irradiation, ethylene oxide, electron beam and X-ray.
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