Lab study: Sterilized reused respirators not effective enough against aerosolized particles – University of Minnesota Twin Cities

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Less than 20% of reused filtering facepiece respirators (FFRs) collected from nurses amid the COVID-19 pandemic were in good enough condition to undergo sterilization, after which none retained at least 94% filtration of aerosol particles, finds a laboratorystudy comparing two sterilization methods after up to 15 to 30 days of use.

For the study, published in the American Journal of Infection Control, a University of Sao Paulo-led team in Brazil used a chambered box and an emitted aerosol to evaluate the physical characteristics and post-sterilization filtration of a 5-centimeter (2-inch) square fragment from each of 100 reused FFRs (eg, N95s) collected from nurses who cared for COVID-19 patients at three hospitals.

Untorn respirators that filtered at least 94% of aerosolized particles and had an attached nasal clip and elastic bands and no visible dirt were randomly assigned to receive or not receive mechanical cleaning with an ultrasonic washer before undergoing hydrogen peroxide plasma gas sterilization.

"During the COVID-19 pandemic, there was a shortage of Filtering Facepiece Respirators (FFR), leading to prolonged use and reuse of FFRs," the authors noted. "There was also an effort to sterilize FFRs aiming to increase the safety of healthcare professionals as it was thought that sterilization could reduce self-contamination and protect the environment from excess contaminated waste."

Of the 1,055 FFRs, over 85% retained secured nose clips, preserved strap elasticity, and no tears. But over 78% of samples were dirty (eg, from makeup), leaving only 19.6% eligible to undergo sterilization. None of the FFRscleaned or uncleanedreached minimum filtration after sterilization, although 72% of the uncleaned FFRs and 80% of the cleaned devices achieved 90.0% to 93.9% filtration.

Sterilization processes using hydrogen peroxide plasma gas, both with and without prior cleaning, applied to 100 FFRs with preserved functionality, did not compromise the apparent physical characteristics of these respirators, but did not maintain their filtration levels to the minimum necessary to be considered safe.

"Sterilization processes using hydrogen peroxide plasma gas, both with and without prior cleaning, applied to 100 FFRs with preserved functionality, did not compromise the apparent physical characteristics of these respirators, but did not maintain their filtration levels to the minimum necessary to be considered safe," the researchers concluded.

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Lab study: Sterilized reused respirators not effective enough against aerosolized particles - University of Minnesota Twin Cities