Three methods effectively sanitized masks for limited re-use
A team of scientists, under the direction of Dr. Vincent Munster in the Laboratory of Virology at Rocky Mountain Laboratory (RML) in Hamilton, working with collaborators from the University of California at Los Angeles, recently released the latest results of a study that validates at least three ways in which N95 respirators may be effectively decontaminated and re-used for a limited number of times. This is great news for healthcare providers and others working on the frontlines in the COVID-19 pandemic which in only a few months has come to cover most of the globe.
Unlike ordinary cloth face masks, carpenter’s dust masks and even surgical masks, N95 respirators have a special inner membrane that can, if it is properly fitted to the individual using it, actually block the virus. They are made for a single use by a single person. But these respirators are in short supply as demand has gone out the ceiling. Being able to confidently re-use them a couple of times after a decontamination process could provide a lot of relief.
“People need to understand that these are not bandanas,” said RML Administrative Director Dr. Marshall Bloom. “These respirators have a specific function in certain kinds of healthcare settings and in certain kinds of laboratory work to protect people from infectious agents in the air,” said Bloom. He said places that use them usually require the people to get “fit-tested” annually to make sure that when a respirator is on a person’s face it is sealed so that air doesn’t infiltrate around it.
“If that respirator doesn’t fit properly, then the person wearing it is not getting the protection that they think they are getting,” said Bloom. He noted that one thing known to be able to defeat the effectiveness of these respirators is facial hair. He recalled a recent newspaper photograph showing a man delivering groceries wearing one of these respirators and he had a big beard. Bloom said the man was not getting the kind of protection he may have been expecting.
“This is something the public should really know,” said Bloom. “You could probably go buy one at Norco, but it would still have to be re-fitted and tested to be sure it doesn’t leak,” he said.
Bloom said the public is getting sort of a sneak preview of the most recent study at the lab concerning the potential decontamination and re-use of the respirators. Given the urgency of the situation, the study results have been posted on a “pre-print server” [medRxiv]so that the information can be shared prior to being peer reviewed and accepted into a journal. Bloom said the work in the study was extremely high quality and he was confident it would be accepted by the journal without substantial modification.
“But nevertheless, they are still both pre-prints,” he said, “and the findings are not yet peer-reviewed but are being shared to assist the public health response to COVID-19.”
According to Bloom, the urgent need for these respirators in the face of this pandemic and the short supply has left many healthcare workers across the country (and the world) dangerously exposed. So, people began asking questions. Can we use these more than once? Can we disinfect and kill the virus that’s on them and then re-use them?
“Can we do this and preserve both the fit and the functioning of the filter in the N95 respirator?” Bloom asked. He said it was a question of considerable practical importance at this time and Dr. Munster in the Laboratory of Virology and his group decided to take on the question.
The first part of the study was done in the Bio-Level 3 section of the lab in Hamilton where they tested the decontamination of small sections of N95 filter fabric that had been exposed to SARS-CoV-2, the virus that causes COVID-19. The four decontamination methods tested included vaporized hydrogen peroxide (VHP); 70-degree Celsius dry heat; ultraviolet light; and 70% ethanol spray. These are all things used in hospitals and are commonly used in medical practice to disinfect equipment and work areas.
All four methods eliminated detectable viable virus from the N95 fabric test samples but some methods worked faster than others. Treatment by VHP proved to be the best option, according to the study. At a concentration of about 1,000 parts per million, the virus on the fabric was rendered undetectable after only 10 minutes. UV and dry heat were acceptable decontamination procedures as long as the methods are applied for at least 60 minutes. Ethanol spray also worked to disinfect the fabric but flunked out in the next part of the testing which took the functionality of the gear into account.
The next part of the study took place outside the lab where investigators treated fully intact, clean respirators with the same decontamination methods to test their reuse durability. Volunteer RML employees wore the masks for two hours to determine if they maintained a proper fit and seal over the face; decontamination was repeated three times with each mask using the same procedure.
The scientists found that ethanol spray damaged the integrity of the respirator’s fit and seal after two decontamination sessions and therefore do not recommend it for decontaminating N95 respirators. UV and heat-treated respirators began showing fit and seal problems after three decontaminations—suggesting these respirators potentially could be re-used twice. The VHP-treated masks experienced no failures, suggesting they potentially could be re-used three times.
“The authors concluded,” Bloom said, “for those people thinking of re-using respirators, that VHP was the most effective decontamination method, because no virus could be detected after only a 10-minute treatment.” He said UV and dry heat were acceptable decontamination procedures as long as the methods are applied for at least 60 minutes. The authors urge anyone decontaminating an N95 respirator to check the fit and seal over the face before each re-use.
Bloom said that the Food and Drug Administration has given emergency use authorization to two companies that produce VHP machines. One machine made by a company called Battell can disinfect up to 80,000 respirators a day. The machines, about the size of a UPS truck or bigger, are being deployed in cities such as Boston, for example. Another company called Sterrad was also authorized.
“This is not a do-it-yourself project with these vaporized hydrogen peroxide machines,” Bloom cautioned. “It’s not like making a smoker out an old refrigerator in the backyard with a hot plate.” He said the substance itself and the process were both dangerous. But essentially the same technology is used in hospitals to disinfect colonoscopes and other instruments. He said any hospital could very well have one of these machines and they could be used to decontaminate these respirators.
Study:
Assessment of N95 respirator decontamination and re-use for SARS-CoV-2. Robert Fischer, http://orcid.org/0000-0002-3655-406X Dylan H Morris, Neeltje van Doremalen, Shanda Sarchette, Jeremiah Matson, Trenton Bushmaker, Claude Kwe Yinda, Stephanie Seifert, Amandine Gamble, Brandi Williamson, Seth Judson, Emmie de Wit, Jamie Lloyd-Smith, Vincent Munster