New research indicates that sterilized and expired N95 respirator masks offer effective protection against coronavirus infection for healthcare workers.
N95 respirator masks as many as 11 years past their expiration date and used N95 respirator masks treated with ethylene oxide or vaporized hydrogen peroxide maintain their filtration efficiency, new research shows.
Limited supply of personal protective equipment was one of the most daunting challenges for U.S. healthcare organizations in the early phase of the coronavirus pandemic. Shortages of N95 respirator masks, which filter at least 95% of 0.3-μm particles and are the gold standard for protection against airborne pathogens, were particularly vexing for healthcare workers and their employers.
The new research, which was published by JAMA Internal Medicine, tested the fitted filtration efficiency (FFE) of 29 fitted facemasks. The fitted facemasks included N95 respirator masks, surgical masks with ties, and procedure masks with ear loops.
The FFE tests were conducted from April to June in a custom-built exposure chamber at the U.S. Environmental Protection Agency Human Studies Facility in Chapel Hill, North Carolina. The testing followed the Occupational Safety and Health Administration's Modified Ambient Aerosol CNC Quantitative Fit Testing Protocol For Filtering Facepiece. Three sterilization methods were tested on used N95 respirator masks: ethylene oxide, steam, and vaporized hydrogen peroxide.
The research generated several key findings:
- N95 respirator masks as many as 11 years past their expiration date retained FFEs more than 95%
- N95 respirator masks treated with ethylene oxide or vaporized hydrogen peroxide retained FFEs more than 95%
- Steam sterilization distorted 1860 N95 respirator masks, rendering them unsuitable for reuse
- Steam sterilization of 1870+ Aura face masks was effective, with the masks retaining more than 95% FFE after a single sterilization cycle
- Chinese-made KN95 respirator masks did not achieve 95% FFE: the Jia Hu Kang KN95 mask with ear loops posted an 85.1% FFE and the Guangdong Fei Fan KN95 posted a 53.2% FFE
- N95 respirator masks that were the wrong size for study participants still had substantial protection, with FFE results between 90% and 95%
- The mean FFE score for surgical masks with ties was 71.5%
- Procedure masks with ear loops had the lowest mean FFE score, at 38.1%
Interpreting the results
New N95 respirator masks are not the only effective face-covering option for clinicians working with coronavirus disease 2019 (COVID-19) patients, the co-authors of the new study wrote.
"This quality-improvement study evaluating 29 face mask alternatives for use by clinicians interacting with patients during the COVID-19 pandemic found that expired N95 respirators and sterilized, used N95 respirators can be used when new N95 respirators are not available. Other alternatives may provide less effective filtration," they wrote.
Sterilization with ethylene oxide (EtO) has one drawback, the co-authors wrote. "A potential disadvantage of EtO sterilization is that the wearer may be exposed to residual EtO within the face mask."
An editorial that accompanied the new study says N95 respirator masks may be preferred in clinical settings with the potential for coronavirus exposure, but they are not necessarily essential.
"Importantly, no documented SARS-CoV-2 outbreaks have been linked to settings in which surgical masks were assiduously used in lieu of N95 masks, which suggests that even if airborne transmission is a considerable contributor to SARS-CoV-2 transmission, surgical masks are likely sufficient to prevent it. Because the infectious dose of virus required to cause clinical infection also remains unknown, it is possible that blocking most, even if not all, viral particles through masks with lower filtration efficiencies of submicron particles is sufficient to prevent disease in the vast majority of cases."
Christopher Cheney is the senior clinical care editor at HealthLeaders.
N95 respirator masks, which have a fitted filtration efficiency score of at least 95% for 0.3-μm particles, are the gold standard for protection against airborne pathogens.
Limited supply of N95 respirator masks has been one of the most conspicuous shortages of personal protective equipment during the coronavirus pandemic.
In new research, procedure masks with ear loops provided the least protection against airborne pathogens, with a fitted filtration efficiency score of 38.1%.