Published in The Journal of Hospital Infection, researchers attempted to disinfect N95 respirators using a SteraMist Binary Ionization Technology.
The main constituent contains 7.8% H2O2 solution which converts to ionized H2O2 (iHP) vapour after passing through a cold plasma arc, and moving like a gas throughout the surface of N95 respirator. The by-product of iHP is oxygen and water in form of humidity.
The experiment was conducted in a well-ventilated room with 6 air-change/per hour inside a biosafety level-2 microbiology laboratory with an operator wearing coverall protection gown. A set of 4 N95 respirators were horizontally hanged up and were inoculated with 10µL each of 3 different concentrations of influenza A virus subtype H1N1 to the outer and inner surfaces. Influenza A virus was chosen because it is an enveloped RNA virus which has similar virological characteristics of coronavirus.
The SteraMist was sprayed in a to-and-fro manner for 3 times at a distance of 24 inches for a total of appropriate 6 seconds treatment time. The influenza A virus inoculated N95 respirators without disinfection were used as positive control. One hour later, the pieces of N95 respirators with virus inoculation were cut out and neutralised. The virus was eluted from the N95 respirators for viral culture in MadinDarby Canine Kidney (MDCK) cell line.
Cytopathic changes of MDCK cells were observed daily for 7 days by light microscopy. All treated pieces did not demonstrate cytopathic changes suggestive of presence of influenza A virus. They were sub-cultured to MDCK cell line again for another 7 days and no sign of cytopathic changes was observed after 7 days. Immunofluorescence staining confirmed the pieces were negative for the influenza A.
“The level of H2O2 on the inner surface of the N95 respirator was 0.6ppm — lower than the safety limit of <1ppm — at 2 hours and undetectable at 3 hours,” the authors wrote. “The speed of H2O2 release from the N95 respirator may be variable and affected by the air current. More importantly, healthcare workers should be well-informed regarding the potential risk of exposure to other chemicals or inert ingredients, which may be persistent in the porous material of N95 respirator. It may pose a dilemma to our healthcare workers who require balancing the risk and benefit of reusing N95 respirators with or without disinfection.
The authors also stated the importance of testing for the particulate filtration efficiency of N95 respirators to determine the maximum number of disinfection cycle regardless of the method of disinfection.
https://www.journalofhospitalinfection.com/article/S0195-6701(20)30178-X/fulltext