key: cord-1021497-rwo8hksl
authors: Kitagawa, Hiroki; Nomura, Toshihito; Nazmul, Tanuza; Kawano, Reo; Omori, Keitaro; Shigemoto, Norifumi; Sakaguchi, Takemasa; Ohge, Hiroki
title: Effect of intermittent irradiation and fluence-response of 222 nm ultraviolet light on SARS-CoV-2 contamination
date: 2021-01-20
journal: Photodiagnosis Photodyn Ther
DOI: 10.1016/j.pdpdt.2021.102184
sha: 9334effed58799303e8e9734dbd810ec96f5d4a5
doc_id: 1021497
cord_uid: rwo8hksl

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(2) 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(2) 222 nm UVC irradiation on SARS-CoV-2 contamination at UV fluences of 1, 2, and 3 mJ/cm(2) 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.

Coronavirus disease 2019 (COVID-19), which is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is currently a global health issue. Studies show that SARS-CoV-2 remains active on plastic and steel surfaces for up to three days [1, 2] .

Furthermore, surfaces in hospitals that are treating COVID-19 patients were found to be contaminated by SARS-CoV-2 [3] , thus suggesting the possibility of indirect transmission via surfaces. However, recent reports have shown the effectiveness of ultraviolet light (UV) irradiation for inactivating SARS-CoV-2 [4] [5] [6] . The effectiveness of 222 nm UVC light for disinfecting surfaces contaminated with SARS-CoV-2 has been reported [7] . In this previous study, the 222 nm UVC-emitting device, Care222 TM (Ushio Inc., Tokyo, Japan; Dimensions: 205 mm x 150 mm x 50 mm) was used and the effect of 0.1 mW/cm 2 222 nm UVC with multiple irradiation times on surfaces contaminated with SARS-CoV-2 was investigated [7] . When Care222 TM was installed on the ceiling or wall, the UV irradiance of distant areas such as desks and floors was lower than that of a previous study setting [7] . Additionally, for use in an occupied space, Care222 TM is used with the on-off intermittent irradiation mode with low UV irradiance or with a motion sensor mode to irradiate 222 nm UVC only when there are no individuals in the room. However, there are no published data on the required fluence and duration of low irradiance 222 nm UVC J o u r n a l P r e -p r o o f radiation for SARS-CoV-2 inactivation. Furthermore, there are no data on the difference between the continuous and intermittent irradiation of 222 nm UVC on SARS-CoV-2 inactivation. The current study evaluated the effectiveness of 222 nm UVC intermittent irradiation (on-off irradiation cycles: 10 s irradiation followed by a 380 s interval) and fluence-dependence of 222 nm UVC irradiation for SARS-CoV-2 inactivation.

SARS-CoV-2/JP/Hiroshima-46059T/2020 was used as the test virus. The cells used in this study and the experimental conditions, including the preparation of SARS-CoV-2contaminated plates and the harvesting of the virus from plates, were the same as those described in a previous report [7] . The virus titer was determined using the standard 50% tissue culture infectious dose (TCID50) method and was expressed as TCID50/mL [7] .

Log10 TCID50/mL reductions were calculated by comparing the log10 TCID50/mL values recovered from plates after 222 nm UVC irradiation with those from control (nonirradiated) plates. to evaluate the differences in infectious viral titers. P-values were computed using a twosided independent-samples t-test. P < 0.05 was considered statistically significant. Figure 1 and Table 2 shows a comparison of the TCID50 assay results of the continuous and intermittent irradiation of 222 nm UV light on SARS-CoV-2 for 5 min. At each irradiance, no significant difference in the log reduction of SARS-CoV-2 was observed. (Table 3-B) .

This study was not a noninferiority trial or equivalence trial, and the sample size was small. However, the error was small, and there was no clinically significant difference in the confidence interval of data among each experiment (Tables 2, 3 A variety of organisms possess molecular mechanisms to compensate for the UV-induced DNA damages. Photoreactivation is one of most widely studied repair mechanisms which uses an enzyme called photolyase and light energy [9] . Photoreactivation causes problems for large-scale UVC inactivation of microorganisms when the treated object such as wastewater or drinking water are exposed to sunlight. However, this result may indicate Previous studies have demonstrated the absence of photoreactivation in most viruses owing to the lack of biological processes such as enzymes and cellular functions that orchestrate photoreactivation [10] . However, a recent report showed that a few viruses such as T1 and PRD1 might undergo photoreactivation via the host bacteria. By contrast, no photoreactivation was observed in MS2 even with hosts [11] . Moreover, we showed that 222 nm UVC inactivates SARS-CoV-2 in a fluence-dependent manner and not in an irradiance-dependent manner, which is consistent with a previous report on other viruses [12] . This result suggested that SARS-CoV-2 can be inactivated by long term irradiation with a low irradiance of 222 nm UVC at a location away from Care222 TM , such as a desk or floor. In occupied space, 222 nm UVC is irradiated by Care222 TM with the on-off intermittent irradiation mode or a motion sensor within the current exposure limits recommended by the American Conference of Governmental Industrial Hygienists for not posing a health risk to humans. The results of this study also suggest that intermittent irradiation with a low irradiance 222 nm UVC and continuous irradiation with a highirradiance 222 nm UV can inactivate SARS-CoV-2 when the total UV fluence is the same.

In conclusion, we demonstrated that there was no significant difference in the inactivation effect of continuous and intermittent irradiation of 222 nm UVC on SARS-CoV-2. 

Aerosol and surface stability of SARS-CoV-2 as compared with SARS-CoV-1

The effect of temperature on persistence of SARS-CoV-2 on common surfaces

Air, surface environmental, and personal protective equipment contamination by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) from a symptomatic patient

Rapid inactivation of SARS-CoV-2 with deep-UV LED irradiation

Susceptibility of SARS-CoV-2 to UV irradiation

Deactivation of SARS-CoV-2 with Pulsed Xenon Ultraviolet: implications for environmental COVID-19 control

Methicillin-resistant Staphylococcus aureus contamination of hospital-use-only mobile phones and efficacy of 222-nm ultraviolet disinfection

UV-induced DNA damage and repair: a review

The Ultraviolet Disinfection Handbook. American Water Works Association

Photoreactivation of bacteriophages after UV disinfection: Role of genome structure and impacts of UV source

Action spectra for validation of pathogen disinfection in medium-pressure ultraviolet (UV) systems

We would like to thank Igarashi T, Ohashi H, Koi T, and Okumura Y (Ushio Inc., Tokyo, Japan) for their technical support and advice. We would like to thank Editage (www.editage.com) for English language editing.