Characterization of a novel, low-cost, scalable ozone gas system for sterilization of N95 respirators and other COVID-19 related use cases.

Abstract

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), an elusive and highly pathogenic agent, has resulted in the ongoing COVID-19 pandemic affecting numerous populations worldwide. New studies investigating the tenacity of SARS-CoV-2 have highlighted its ability to persist on a myriad of surfaces for several days, including gowns and shoes. As a result, there is a global need for sterilization of a variety of potentially-contaminated items, ranging from clothing to personal protective equipment like face coverings. To this end, we have designed and constructed a cost-effective, scalable, and sustainable sterilization system that uses ozone gas to inactivate viral particles. We sought to determine the efficacy of the system in the sterilization of viral particles as well as its ability to sterilize N95 respirators for reuse. N95 respirators inoculated with P22 bacteriophage and sterilized in the ozone system showed a 6-log10 reduction in viral load when treated at 25 ppm for 150 minutes. Further, N95 respirators treated with five 150-minute cycles at 35 ppm for a total concentration-time product (CT) of 26,250 ppm⋅min in the ozone system showed comparable filtration efficiency to untreated N95 respirators in a 50 to 200 nmr particulate challenge filtration test. Interestingly, the surgical N95 respirators tested showed complete inactivation of fluid resistance and degradation of the elasticity of polyisoprene straps after five cycles in the sterilization system. Taken together, these data suggest that while our ozone system may negatively affect certain protective aspects of surgical N95 respirators, it does effectively sterilize viral particles and can be utilized for a multitude of other use cases, including sterilizing polypropylene face coverings after potential SARS-CoV-2 contamination. In addition to providing long-term environmental benefits, deployment of this system during the ongoing pandemic reduces the risk of COVID-19 community transmission while conserving monetary resources otherwise spent on the continuous purchase of disposable face coverings.

Can ozone inactivate SARS-CoV-2? A review of mechanisms and performance on viruses

“…Accordingly, all the works where O 3 was supplied in aqueous solution, where bacteria were the main target, or where ozone was used as a medical therapy, were discarded. Three of the works considered in this review have been recently published as pre-print ( Blanchard et al, 2020 , Dave et al, 2020 , Lee et al, 2020 ), as a direct response to the current COVID-19 pandemic. Since they present a rigorous scientific approach and due to the interest of their topic, they have been included.…”

“… 25 150 7.357 N95 Resp. 6.4 room ( Dave et al, 2020 ) c Poliovirus NO 0-28 a 60 2.500 glass surface 2.0 40 20 ( Hudson et al, 2009 ) Poliovirus NO 0-20 a 60 1.800 polystyrene 2.9 70 room ( Hudson et al, 2009 ) Poliovirus NO 0-20 a 60 1.800 polystyrene 0.0 38 room ( Hudson et al, 2009 ) Poliovirus NO 0-20 a 60 1.800 undetermined 3.0 40-95 room ( Hudson et al, 2009 ) Poliovirus type I Sabin vaccine NO 0.64 3960 4.780 aqueous layer 0.0 …”

“… ( Dubuis et al, 2020 , Kekez and Sattar, 1997 , Tseng and Li, 2008 , Tseng and Li, 2006 ) Murine Hepatitis Virus MHV coronaviridiae YES 1 representative betacoronavirus, possible surrogate for SARS virus ssRNA (+), 26-32 kB pleomorphic, spherical or bacilliform 75-220 nm ( Sato et al, 1990 ) Murine norovirus MNV Caliciviridae NO 5 Surrogate for human norovirus ssRNA (+) 7.4-8.3 kB icosahedral, 27–40 nm ( Brié et al, 2018 , Cannon et al, 2013 , Dubuis et al, 2020 , Hudson et al, 2007 , Predmore et al, 2015 ) P22 P22 Podoviridae NO 1 phage virus, well-known widely used dsDNA 40-42 kB head-tail structure, with a T=7 laevo icosahedral symmetry. 60-65 m ( Dave et al, 2020 ) Poliovirus PV Picornaviridae NO 2 enteric virus, causative of polio ssRNA (+) 6.7–10.1 kB 30–32 nm icosahedral virions comprising 60 protomers ( Bolton et al, 1982 , Hudson et al, 2009 ) PR772 PR772 Tectiviridae NO 1 phage virus, model for adenovirus linear dsDNA, 15 kb icosahedral virion with a pseudo T=25 symmetry.66-80 nm with apical spikes of 20 nm. ( Dubuis et al, 2020 ) Reo type 3 virus RT3 reoviridae NO 1 dsRNA virus, 18.2-30.5 kB icosahedral virion, multilayer capsid structure, 60-80 nm ( ...…”

“…Among the rest of works focused on the study of the efficacy of ozone for inactivating viruses from surfaces or fomites ( Table 2 ), three of them have been also recently published as a response to the COVID-19 sanitary emergency, studying the disinfection of personal protective equipment (PPE) for its safe reuse ( Blanchard et al, 2020 , Dave et al, 2020 , Lee et al, 2020 ). Different types of viruses (most of them enveloped and close to SARS-CoV-2) were tested on different PPE: face masks ( Blanchard et al, 2020 , Lee et al, 2020 ), Tyvek fabric (employed in disposable gowns and PAPR hoods) ( Blanchard et al, 2020 ) and N95 face respirators ( Blanchard et al, 2020 , Dave et al, 2020 ). Additionally, the authors of the three reports examined if the materials had undergone changes after ozone treatment and in all cases their protective function was unaffected, being only the elastic straps altered after treatment.…”

“…2 , Fig. 3 show CT value versus the virus inactivation in aerosols (from 4 publications ( de Mik and de Groot, 1977 ; Dubuis et al, 2020 ; Kekez and Sattar, 1997 ; Tseng and Li, 2006 )) and on surfaces (from 10 publications: ( Blanchard et al, 2020 , Cannon et al, 2013 , Dave et al, 2020 , Hudson et al, 2009 , Lee et al, 2020 , Predmore et al, 2015 , Tanaka et al, 2009 , Tseng and Li, 2008 , Yano et al, 2020 ) according to full data in Tables S1 and S2 respectively. Only those experiments with a RH between 65%-95% (near optimal conditions) and inactivation quantification by plaque forming units (PFU) assay or the tissue culture infective dose have been included.…”