key: cord-1040166-idgjx57a authors: Percivalle, E.; Clerici, M.; Cassaniti, I.; Nepita, E. Vecchio; Marchese, P.; Olivati, D.; Catelli, C.; Berri, A.; Baldanti, F.; Marone, P.; Bruno, R.; Triarico, A.; Lago, P. title: SARS-CoV-2 viability on different surfaces after gaseous ozone treatment: a preliminary evaluation date: 2021-01-28 journal: J Hosp Infect DOI: 10.1016/j.jhin.2021.01.014 sha: 2d1820d292c6eacc4ed7510f57081591564ce891 doc_id: 1040166 cord_uid: idgjx57a COVID-19 is a global health threat with a huge number of confirmed cases and deaths all over the world. Human-to-human transmission via respiratory droplets and contact with aerosol-infected surfaces are the major routes of virus spread. Because SARS-CoV-2 can remain in the air and on surfaces from several hours to several days, disinfection of frequently touched surfaces and critical rooms, in addition to observing individual hygiene tips, is required to reduce the virus spreading. Here we report on an investigation into the use of gaseous ozone as a potentially effective sanitizing method against the new coronavirus. A novel human coronavirus, named severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), emerged in Wuhan -China -in late 2019 and caused a pandemic, spreading worldwide and posing a huge global health threat. The total number of global deaths due to the COVID-19 (SARS-CoV-2-caused disease) at the end of September 2020 had risen to 991 224, with 37 730 945 infected (1) . To deal with this pandemic, in addition to research in medical field, the main health measures recommended by World Health Organization (WHO) have focused on social distancing and lockdown, as well as application of a safety protocols, adoption of hygiene measures and use of personal protection equipment (PPE), such as masks, gloves, etc. To adopt effective countermeasures to contain the pandemic and minimize the death toll, it is imperative to recognize all routes of possible virus transmission. Increasing recent evidences suggested that human-to-human transmission is primarily achieved through close contact of respiratory droplets, direct contact with infected individuals or by contact with contaminated objects and surfaces. Aerosol transmission seems to be the most important route of SARS-CoV-2 infection: this virus is able to maintain its infectivity and virion integrity up to 16 hours in respirable-sized aerosols in closed rooms (2) . Moreover it has been demonstrated that viable virus can be isolated from air samples collected up to 4.8 meters away from a COVID-19 patient in hospital room (3) . While the primary spread of SARS-CoV-2 appears to be via aerosols and respiratory droplets, fomites may be also an important contributor in virus transmission, as demonstrated for other coronaviruses (as for NL63, 229E and MERS-CoV). Indeed, viruses are able to survive on surfaces for extended periods, sometimes up to months. Once contaminated from the environment, hands can then initiate a self-inoculation of mucous membranes of the nose, eyes or mouth. Fathizadeh et al. (4) showed that SARS-CoV-2 can persist on a variety of surfaces from hours to days, allowing the transmission via surface contact: up to 4 hours on copper, up to 8 hours on latex gloves, 2 days on surgical gowns, 2-3 days on steel, 4 days on glass, 4-5 days on wood, 5 days on metal, from 4 days to 9 days on plastic and from 1 day to 5 days on paper. Riddel et al. (5) demonstrated that infectious SARS-CoV-2 can be recovered from four different and common non porous surfaces -banknotes, stainless steel, glass, vinyl -for at least 28 days (at RT and 50% RH). In addition, Chin et al. (6) demonstrated that the virus is more stable on smooth surfaces: a significant level of SARS-CoV-2 has been detected on the outer surface of surgical masks on day 7 after infection. The aim of this preliminary evaluation was to investigate the efficacy of gaseous ozone on SARS-CoV-2 viability on different surfaces. This was in order to assess the feasibility of gaseous ozone as a potential effective sanitizing method to remove the virus from a high-risk indoor rooms (such as hospital and nursing rooms), hard to reach and critical surfaces (where other disinfectants cannot be used) and medical equipment., for which pivotal precautions must be planned and taken. All experimental steps with SARS-CoV-2 were performed under conditions of biosafety level 3 containment. The results are summarized in Figure 1 . pandemic. Indeed, healthcare workers are in the front line of the COVID-19 outbreak response and are exposed to a high risk of SARS-CoV-2 infection daily. PPE (gowns, masks, gloves) is their main defence against viral contamination. While most PPE were designated for single use, during the COVID-19 pandemic re-use of them was considered, requiring effective and fast treatment conserving material properties. This could reduce consumption (increasing availability) and waste products (decreasing environmental impact). The virucidal efficacy of ozone did not seem to be directly proportional to its concentration and was not dependent on surface type. Therefore, gaseous ozone could be a useful and widely accessible method to significantly reduce the infectious SARS-CoV-2 from almost all medical equipment and surfaces not susceptible to corrosion. It could help in reducing virus spreading, mostly in high risk rooms/areas in healthcare facilities, and on hard to reach critical surfaces as a better alternative to disinfectants. Ozone may react with viruses through direct molecular interaction and/or indirectly through reactive oxygen species (ROS), produced as a result of ozone decomposition. In addition, the reaction between ozone and its ROS with the constituents of the virus structure (including lipids, proteins and amino acids) could lead to the formation of other ROS, including reactive radicals, which further propagate oxidation through a chain reaction. As already assumed by Tizaoui (8) , ozone, via an oxidative process, could attacks the proteins and lipids of the SARS-CoV-2's spikes and envelope, destroying the virus integrity and inhibiting the mechanism by which it infects. There are many advantages in using ozone as a surfaces and rooms sanitizer. Ozone is a much more potent oxidizer than other common disinfectants (such as chlorine and hypochlorite), with a wide biocidal effect, guaranteeing a meaningful reduction of airborne microorganisms. As a gas, ozone can penetrates into every room corner, reaching all surfaces, and so is much more efficient than manually applied liquid sprays and aerosols. As an unstable gas, ozone is generated on-site and on-demand and it is readily converted back to oxygen, leaving no harmful residuals (ozone is environmentally friendly). Although gaseous ozone is effective and advantageous in sanitizing processes, it presents risks for people safety and health if it is not properly handled. When inhaled, ozone can damage the lungs, causing chest pain, coughing, shortness of breath and throat irritation. Ozone may also worsen chronic respiratory diseases, such as asthma. Therefore, it is necessary to take adequate safety measures during its use. Healthcare buildings, such as hospitals and elderly care facilities, host vulnerable people making it especially important to plan ozone sanitizing. It is also considered one of the secondary pollutant components of photochemical smog, which produces effects on human health and property. These health hazards can be overcome in practice by removing gaseous ozone after treatment using a catalytic converter. Ozone is a strong oxidizing agent, reacting with organic compounds and inducing corrosion of certain materials. Sensitive materials such as natural rubber need to be removed or temporarily covered, to protect against corrosion. The same experiments as in figure 1 The longer survival of SARS-CoV-2 at low temperature and low environmental RH may at least partly explain the observed peaks of COVID-19 cases during the cold and dry seasons in temperate regions, and is consistent with the seasonality of other respiratory viruses such as influenza virus. In conclusion, alongside recommended WHO countermeasures (social distancing, wearing a mask, etc.), using gaseous ozone as a sanitizing method for high risk indoor rooms and critical or hard to reach surfaces, especially in healthcare facilities, could help to reduce virus spread, keeping patients and healthcare professionals safe during the current pandemic. Further studies are required to confirm ozone efficacy in different conditions, potentially expanding possible applications. WHO -Health Emergency Dashboard. World Health Organization Coronavirus Disease (COVID-19) Dashboard 2020 Persistence of severe acute respiratory syndrome coronavirus 2 in aerosol suspensions Viable SARS-CoV-2 in the air of hospital room with COVID-19 patients Protection and disinfection policies against SARS-CoV-2 (COVID 19) The effect of temperature on persistence of SARS-CoV-2 on common surfaces Stability of SARS-CoV-2 in different environmental conditions Development of a practical method for using ozone gas as a virus decontaminating agent Ozone: A potential oxidant for COVID-19 virus (SARS-CoV-2) Stability of SARS-CoV-2 and other coronaviruses in the environment and on common touch surfaces and the influence of climatic conditions: A review Increasing temperature and relative humidity accelerates inactivation of SARS-CoV-2 on surfaces Reduction of SARS-CoV-2 viability on different surfaces after gaseous ozone fumigation SARS-CoV-2 viability reduction percentage after fumigation with gaseous ozone 0.5 ppm, 1 ppm and 2 ppm on eight different surfaces: painted aluminum, not-painted aluminum, FFP2 mask, surgical gown, glass, plexiglas, plastic and stainless steel All experiments were performed at controlled and steady RH (55%) and temperature (24°C) The authors would like to thank the COVID-19 IRCCS San Matteo Pavia Task Force for the job done during the emergency period and for the support received for the laboratory experiments. None declared. This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sector.