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    Effect of intermittent irradiation and fluence-response of 222 nm ultraviolet light on SARS-CoV-2 contamination. Kitagawa Hiroki,Nomura Toshihito,Nazmul Tanuza,Kawano Reo,Omori Keitaro,Shigemoto Norifumi,Sakaguchi Takemasa,Ohge Hiroki Photodiagnosis and photodynamic therapy BACKGROUND:The effectiveness of 222 nm ultraviolet (UV) C light for disinfecting surfaces contaminated with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has been reported. The aim of this study was to evaluate the effect of the intermittent irradiation of 222 nm UVC on SARS-CoV-2 and the fluence-dependent effect of 222 nm UVC irradiation on SARS-CoV-2 inactivation. METHODS:We experimented with 5 min continuous and intermittent irradiation for 0.1, 0.05, 0.013, and 0.003 mW/cm of 222 nm UVC to evaluate the differences in the effect of the continuous and intermittent irradiation of 222 nm UVC on SARS-CoV-2 inactivation. For intermittent irradiation, we followed the on-off irradiation cycles with every 10-s irradiation followed by a 380-s interval. Thereafter, we evaluated the effects of 0.1, 0.013, and 0.003 mW/cm 222 nm UVC irradiation on SARS-CoV-2 contamination at UV fluences of 1, 2, and 3 mJ/cm at each irradiance. RESULTS:At each irradiance, no significant difference was observed in the log reduction of SARS-CoV-2 between continuous and intermittent irradiation. At each UV fluence, no significant difference was observed in the log reduction of SARS-CoV-2 among the three different irradiance levels. CONCLUSION:There was no significant difference between continuous and intermittent irradiation with 222 nm UVC with regards to SARS-CoV-2 inactivation. Moreover, 222 nm UVC inactivates SARS-CoV-2 in a fluence-dependent manner. The efficacy of 222-nm UVC irradiation in reducing the contamination of SARS-CoV-2 needs to be further evaluated in a real-world setting. 10.1016/j.pdpdt.2021.102184
    Inactivation Rates for Airborne Human Coronavirus by Low Doses of 222 nm Far-UVC Radiation. Viruses Recent research using UV radiation with wavelengths in the 200-235 nm range, often referred to as far-UVC, suggests that the minimal health hazard associated with these wavelengths will allow direct use of far-UVC radiation within occupied indoor spaces to provide continuous disinfection. Earlier experimental studies estimated the susceptibility of airborne human coronavirus OC43 exposed to 222-nm radiation based on fitting an exponential dose-response curve to the data. The current study extends the results to a wider range of doses of 222 nm far-UVC radiation and uses a computational model coupling radiation transport and computational fluid dynamics to improve dosimetry estimates. The new results suggest that the inactivation of human coronavirus OC43 within our exposure system is better described using a bi-exponential dose-response relation, and the estimated susceptibility constant at low doses-the relevant parameter for realistic low dose rate exposures-was 12.4 ± 0.4 cm/mJ, which described the behavior of 99.7% ± 0.05% of the virus population. This new estimate is more than double the earlier susceptibility constant estimates that were based on a single-exponential dose response. These new results offer further evidence as to the efficacy of far-UVC to inactivate airborne pathogens. 10.3390/v14040684
    Effectiveness of 222-nm ultraviolet light on disinfecting SARS-CoV-2 surface contamination. Kitagawa Hiroki,Nomura Toshihito,Nazmul Tanuza,Omori Keitaro,Shigemoto Norifumi,Sakaguchi Takemasa,Ohge Hiroki American journal of infection control BACKGROUND:Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which causes coronavirus disease 2019 (COVID-19), has emerged as a serious threat to human health worldwide. Efficient disinfection of surfaces contaminated with SARS-CoV-2 may help prevent its spread. This study aimed to investigate the in vitro efficacy of 222-nm far-ultraviolet light (UVC) on the disinfection of SARS-CoV-2 surface contamination. METHODS:We investigated the titer of SARS-CoV-2 after UV irradiation (0.1 mW/cm) at 222 nm for 10-300 seconds using the 50% tissue culture infectious dose (TCID). In addition, we used quantitative reverse transcription polymerase chain reaction to quantify SARS-CoV-2 RNA under the same conditions. RESULTS:One and 3 mJ/cm of 222-nm UVC irradiation (0.1 mW/cm for 10 and 30 seconds) resulted in 88.5 and 99.7% reduction of viable SARS-CoV-2 based on the TCID assay, respectively. In contrast, the copy number of SARS-CoV-2 RNA did not change after UVC irradiation even after a 5-minute irradiation. CONCLUSIONS:This study shows the efficacy of 222-nm UVC irradiation against SARS-CoV-2 contamination in an in vitro experiment. Further evaluation of the safety and efficacy of 222-nm UVC irradiation in reducing the contamination of real-world surfaces and the potential transmission of SARS-CoV-2 is needed. 10.1016/j.ajic.2020.08.022
    Clinical application of 222 nm wavelength ultraviolet C irradiation on SARS CoV-2 contaminated environments. Su Wen-Lin,Lin Chih-Pei,Huang Hui-Ching,Wu Yao-Kuang,Yang Mei-Chen,Chiu Sheg-Kang,Peng Ming-Yieh,Chan Ming-Chin,Chao You-Chen Journal of microbiology, immunology, and infection = Wei mian yu gan ran za zhi This was a preliminary study on ultraviolet C (UVC) irradiation for SARS-CoV-2-contaminated hospital environments. Forty-eight locations were tested for SARS-CoV-2 using RT-PCR (33.3% contamination rate). After series dosages of 222-nm UVC irradiation, samples from the surfaces were negative at 15 s irradiation at 2 cm length (fluence: 81 mJ/cm). 10.1016/j.jmii.2021.12.005
    Far-UVC (222 nm) efficiently inactivates an airborne pathogen in a room-sized chamber. Eadie Ewan,Hiwar Waseem,Fletcher Louise,Tidswell Emma,O'Mahoney Paul,Buonanno Manuela,Welch David,Adamson Catherine S,Brenner David J,Noakes Catherine,Wood Kenneth Scientific reports Many infectious diseases, including COVID-19, are transmitted by airborne pathogens. There is a need for effective environmental control measures which, ideally, are not reliant on human behaviour. One potential solution is Krypton Chloride (KrCl) excimer lamps (often referred to as Far-UVC), which can efficiently inactivate pathogens, such as coronaviruses and influenza, in air. Research demonstrates that when KrCl lamps are filtered to remove longer-wavelength ultraviolet emissions they do not induce acute reactions in the skin or eyes, nor delayed effects such as skin cancer. While there is laboratory evidence for Far-UVC efficacy, there is limited evidence in full-sized rooms. For the first time, we show that Far-UVC deployed in a room-sized chamber effectively inactivates aerosolised Staphylococcus aureus. At a room ventilation rate of 3 air-changes-per-hour (ACH), with 5 filtered-sources the steady-state pathogen load was reduced by 98.4% providing an additional 184 equivalent air changes (eACH). This reduction was achieved using Far-UVC irradiances consistent with current American Conference of Governmental Industrial Hygienists threshold limit values for skin for a continuous 8-h exposure. Our data indicate that Far-UVC is likely to be more effective against common airborne viruses, including SARS-CoV-2, than bacteria and should thus be an effective and "hands-off" technology to reduce airborne disease transmission. The findings provide room-scale data to support the design and development of effective Far-UVC systems. 10.1038/s41598-022-08462-z
    Extreme Exposure to Filtered Far-UVC: A Case Study. Eadie Ewan,Barnard Isla M R,Ibbotson Sally H,Wood Kenneth Photochemistry and photobiology Far-UVC devices are being commercially sold as "safe for humans" for the inactivation of SARS-CoV-2, without supporting human safety data. We felt there was a need for rapid proof-of-concept human self-exposure, to inform future controlled research and promote informed discussion. A Fitzpatrick Skin Type II individual exposed their inner forearms to large radiant exposures from a filtered Krypton-Chloride (KrCl) far-UVC system (SafeZoneUVC, Ushio Inc., Tokyo, Japan) with peak emission at 222 nm. No visible skin changes were observed at 1500 mJ cm ; whereas, skin yellowing that appeared immediately and resolved within 24 h occurred with a 6000 mJ cm exposure. No erythema was observed at any time point with exposures up to 18 000 mJ cm . These results combined with Monte Carlo Radiative Transfer computer modeling suggest that filtering longer ultraviolet wavelengths is critical for the human skin safety of far-UVC devices. This work also contributes to growing arguments for the exploration of exposure limit expansion, which would subsequently enable faster inactivation of viruses. 10.1111/php.13385
    UVC-based photoinactivation as an efficient tool to control the transmission of coronaviruses. Bhardwaj Sanjeev K,Singh Harpreet,Deep Akash,Khatri Madhu,Bhaumik Jayeeta,Kim Ki-Hyun,Bhardwaj Neha The Science of the total environment The ongoing COVID-19 pandemic made us re-realize the importance of environmental disinfection and sanitation in indoor areas, hospitals, and clinical rooms. UVC irradiation of high energy and short wavelengths, especially in the 200-290-nm range possesses the great potential for germicidal disinfection. These properties of UVC allow to damage or destruct the nucleic acids (DNA/RNA) in diverse microbes (e.g., bacteria, fungi, and viruses). UVC light can hence be used as a promising tool for prevention and control of their infection or transmission. The present review offers insights into the historical perspective, mode of action, and recent advancements in the application of UVC-based antiviral therapy against coronaviruses (including SARS CoV-2). Moreover, the application of UVC lights in the sanitization of healthcare units, public places, medical instruments, respirators, and personal protective equipment (PPE) is also discussed. This article, therefore, is expected to deliver a new path for the developments of UVC-based viricidal approach. 10.1016/j.scitotenv.2021.148548
    Far-UVC light (222 nm) efficiently and safely inactivates airborne human coronaviruses. Buonanno Manuela,Welch David,Shuryak Igor,Brenner David J Scientific reports A direct approach to limit airborne viral transmissions is to inactivate them within a short time of their production. Germicidal ultraviolet light, typically at 254 nm, is effective in this context but, used directly, can be a health hazard to skin and eyes. By contrast, far-UVC light (207-222 nm) efficiently kills pathogens potentially without harm to exposed human tissues. We previously demonstrated that 222-nm far-UVC light efficiently kills airborne influenza virus and we extend those studies to explore far-UVC efficacy against airborne human coronaviruses alpha HCoV-229E and beta HCoV-OC43. Low doses of 1.7 and 1.2 mJ/cm inactivated 99.9% of aerosolized coronavirus 229E and OC43, respectively. As all human coronaviruses have similar genomic sizes, far-UVC light would be expected to show similar inactivation efficiency against other human coronaviruses including SARS-CoV-2. Based on the beta-HCoV-OC43 results, continuous far-UVC exposure in occupied public locations at the current regulatory exposure limit (~3 mJ/cm/hour) would result in ~90% viral inactivation in ~8 minutes, 95% in ~11 minutes, 99% in ~16 minutes and 99.9% inactivation in ~25 minutes. Thus while staying within current regulatory dose limits, low-dose-rate far-UVC exposure can potentially safely provide a major reduction in the ambient level of airborne coronaviruses in occupied public locations. 10.1038/s41598-020-67211-2