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Effectiveness of 222-nm ultraviolet light on disinfecting SARS-CoV-2 surface contamination

  • Hiroki Kitagawa
    Correspondence
    Address correspondence to Hiroki Kitagawa, MD, Department of Infectious Diseases, Hiroshima University Hospital, 1-2-3 Kasumi, Minami-Ku, Hiroshima 734-8551, Japan.
    Affiliations
    Project Research Center for Nosocomial Infectious Diseases, Hiroshima University, Hiroshima, Japan

    Department of Infectious Diseases, Hiroshima University Hospital, Hiroshima, Japan

    Department of Surgery, Graduate School of Biomedical and Health Sciences, Hiroshima University, Hiroshima, Japan
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  • Toshihito Nomura
    Affiliations
    Department of Infectious Diseases, Hiroshima University Hospital, Hiroshima, Japan

    Department of Virology, Graduate School of Biomedical and Health Sciences, Hiroshima University, Hiroshima, Japan
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  • Tanuza Nazmul
    Affiliations
    Department of Virology, Graduate School of Biomedical and Health Sciences, Hiroshima University, Hiroshima, Japan
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  • Keitaro Omori
    Affiliations
    Department of Infectious Diseases, Hiroshima University Hospital, Hiroshima, Japan
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  • Norifumi Shigemoto
    Affiliations
    Project Research Center for Nosocomial Infectious Diseases, Hiroshima University, Hiroshima, Japan

    Department of Infectious Diseases, Hiroshima University Hospital, Hiroshima, Japan

    Department of Surgery, Graduate School of Biomedical and Health Sciences, Hiroshima University, Hiroshima, Japan

    Translational Research Center, Hiroshima University, Hiroshima, Japan
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  • Takemasa Sakaguchi
    Affiliations
    Department of Virology, Graduate School of Biomedical and Health Sciences, Hiroshima University, Hiroshima, Japan
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  • Hiroki Ohge
    Affiliations
    Project Research Center for Nosocomial Infectious Diseases, Hiroshima University, Hiroshima, Japan

    Department of Infectious Diseases, Hiroshima University Hospital, Hiroshima, Japan
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Open AccessPublished:September 04, 2020DOI:https://doi.org/10.1016/j.ajic.2020.08.022

      Highlights

      • 222-nm UVC light (0.1 mW/cm2) reduced viable SARS-CoV-2 by 0.94 log10 in 10 seconds.
      • 222-nm UVC light (0.1 mW/cm2) reduced viable SARS-CoV-2 by 2.51 log10 in 30 seconds.
      • 222-nm UVC light did not reduce SARS-CoV-2 RNA copy number after 5-minute irradiation.
      • TSID50 and not RT-qPCR should be used to monitor far-UVC disinfection of surfaces.

      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/cm2) at 222 nm for 10-300 seconds using the 50% tissue culture infectious dose (TCID50). 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/cm2 of 222-nm UVC irradiation (0.1 mW/cm2 for 10 and 30 seconds) resulted in 88.5 and 99.7% reduction of viable SARS-CoV-2 based on the TCID50 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.

      Key Words

      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.
      • Li Q
      • Guan X
      • Wu P
      • et al.
      Early transmission dynamics in Wuhan, China, of novel coronavirus-infected pneumonia.
      ,
      • Huang C
      • Wang Y
      • Li X
      • et al.
      Clinical features of patients infected with 2019 novel coronavirus in Wuhan, China.
      SARS-CoV-2 is mainly transmitted through infected respiratory droplets and close contact with infected people. Recent studies showed that SARS-CoV-2 can remain viable for days on surfaces under controlled experimental conditions.
      • van Doremalen N
      • Bushmaker T
      • Morris DH
      • et al.
      Aerosol and surface stability of SARS-CoV-2 as compared with SARS-CoV-1.
      ,
      • Kampf G
      • Todt D
      • Pfaender S
      • Steinmann E
      Persistence of coronaviruses on inanimate surfaces and their inactivation with biocidal agents.
      Furthermore, surfaces in hospitals treating patients with COVID-19 were found to be contaminated by SARS-CoV-2, suggesting that the hospital environment could be a potential medium of transmission.
      • Wu S
      • Wang Y
      • Jin X
      • Tian J
      • Liu J
      • Mao Y
      Environmental contamination by SARS-CoV-2 in a designated hospital for coronavirus disease 2019.
      • Ong SWX
      • Tan YK
      • Chia PY
      • et al.
      Air, surface environmental, and personal protective equipment contamination by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) from a symptomatic patient.
      • Ye G
      • Lin H
      • Chen S
      • et al.
      Environmental contamination of SARS-CoV-2 in healthcare premises.
      Therefore, if environmental disinfection is not effective, SARS-CoV-2 may spread widely and cause nosocomial infections.
      Recently, ultraviolet (UV) light disinfection systems have been increasingly used in health care settings in an attempt to decrease the transmission of nosocomial pathogens and prevent health care-associated infections.
      • Marra AR
      • Schweizer ML
      • Edmond MB
      No-touch disinfection methods to decrease multidrug-resistant organism infections: a systematic review and meta-analysis.
      Most UV disinfection systems use germicidal lamps emitting UV radiation C (UVC) around 254 nm. However, it is well known that 254-nm UVC is harmful to the skin and eyes. Previous reports demonstrated that 222-nm UVC light, belonging to far-UVC (207-222 nm), has the same highly effective germicidal properties as 254-nm UVC; however, it is less harmful to the skin and eyes than 254-nm UVC because far-UVC light has a very limited penetration depth in the skin or eye.
      • Buonanno M
      • Ponnaiya B
      • Welch D
      • et al.
      Germicidal efficacy and mammalian skin safety of 222-nm UV light.
      • Narita K
      • Asano K
      • Morimoto Y
      • et al.
      Disinfection and healing effects of 222-nm UVC light on methicillin-resistant Staphylococcus aureus infection in mouse wounds.
      • Narita K
      • Asano K
      • Morimoto Y
      • Igarashi T
      • Nakane A
      Chronic irradiation with 222-nm UVC light induces neither DNA damage nor epidermal lesions in mouse skin, even at high doses.
      • Yamano N
      • Kunisada M
      • Kaidzu S
      • et al.
      Long-term effects of 222-nm ultraviolet radiation C sterilizing lamps on mice susceptible to ultraviolet radiation.
      • Narita K
      • Asano K
      • Naito K
      • et al.
      Ultraviolet C light with wavelength of 222 nm inactivates a wide spectrum of microbial pathogens.
      In addition, previous studies have reported that low dose of 222-nm UVC inactivated aerosolized H1N1 influenza virus and human coronaviruses alpha HCoV-229E and beta HCoV-OC43.
      • Welch D
      • Buonanno M
      • Grilj V
      • et al.
      Far-UVC light: a new tool to control the spread of airborne-mediated microbial diseases.
      ,
      • Buonanno M
      • Welch D
      • Shuryak I
      • Brenner DJ
      Far-UVC light (222 nm) efficiently and safely inactivates airborne human coronaviruses.
      Although there are a few reports about the effectiveness of UV disinfection on SARS-CoV-2,
      • Simmons S
      • Carrion R
      • Alfson K
      • et al.
      Deactivation of SARS-CoV-2 with pulsed xenon ultraviolet: Implications for environmental COVID-19 control [e-pub ahead of print].
      ,
      • Heilingloh CS
      • Aufderhorst UW
      • Schipper L
      • et al.
      Susceptibility of SARS-CoV-2 to UV irradiation.
      the effect of 222-nm UVC on SARS-CoV-2 is poorly understood. The aim of this study was to investigate the in vitro efficacy of 222-nm UV disinfection of SARS-CoV-2 contamination.

      Methods

      Cells and virus

      VeroE6/TMPRSS2 cells (African green monkey kidney-derived cells expressing human TMPRSS2, purchased from Japanese Collection of Research Bioresources (JCRB) Cell Bank, JCRB1819)
      • Matsuyama S
      • Nao N
      • Shirato K
      • et al.
      Enhanced isolation of SARS-CoV-2 by TMPRSS2-expressing cells.
      were propagated in Dulbecco's modified Eagle's minimum essential medium (DMEM, Invitrogen) supplemented with 10% fetal calf serum (FCS; Biosera, Kansas City, MO), penicillin G (100 units/mL, Meiji Seika Pharma, Tokyo, Japan), and streptomycin (100 µg/mL, Meiji Seika Pharma). The cells were cultured at 37°C in 5% CO2. SARS-CoV-2 2019-nCoV/Japan/AI/I-004/2020 strain was provided by the National Institute of Infectious Diseases, Japan. To prepare virus suspensions, VeroE6/TMPRSS2 cells were infected with the virus and incubated in DMEM. When cytopathic effects were fully developed, the culture supernatant was harvested and filtered through a 0.45-µm filter. The virus titer was determined by the standard 50% tissue culture infectious dose (TCID50) method and expressed as TCID50/mL, as described previously.
      • Ueda K
      • Kawabata R
      • Irie T
      • Nakai Y
      • Tohya Y
      • Sakaguchi T
      Inactivation of pathogenic viruses by plant-derived tannins: strong effects of extracts from persimmon (Diospyros kaki) on a broad range of viruses.
      Viral suspensions (100 µL) containing ca. 5 × 106 TCID50/mL were loaded onto a sterile polystyrene plate (9-cm diameter) and spread into a circle with a diameter of approximately 7 cm. The inoculum was allowed to dry under sterile laminar flow in a biosafety cabinet at room temperature. A total of 5 plates were prepared in triplicate for a nonirradiated control and for 222-nm UV disinfection for 10, 30, 60, and 300 seconds. All experiments with SARS-CoV-2 virus were performed in a biosafety level 3 (BSL3) containment facility at Hiroshima University. All experimental results are reported as means across 3 replicates.

      222-nm UVC disinfection

      The Care222 (Ushio Inc., Tokyo, Japan) UVC emitting device used in this study was a 222-nm krypton-chloride (Kr-Cl) excimer lamp module. The lamp contains an optical filter that removes essentially all but the dominant 222-nm emission wavelength.
      • Buonanno M
      • Ponnaiya B
      • Welch D
      • et al.
      Germicidal efficacy and mammalian skin safety of 222-nm UV light.
      • Narita K
      • Asano K
      • Morimoto Y
      • et al.
      Disinfection and healing effects of 222-nm UVC light on methicillin-resistant Staphylococcus aureus infection in mouse wounds.
      • Narita K
      • Asano K
      • Morimoto Y
      • Igarashi T
      • Nakane A
      Chronic irradiation with 222-nm UVC light induces neither DNA damage nor epidermal lesions in mouse skin, even at high doses.
      • Yamano N
      • Kunisada M
      • Kaidzu S
      • et al.
      Long-term effects of 222-nm ultraviolet radiation C sterilizing lamps on mice susceptible to ultraviolet radiation.
      • Narita K
      • Asano K
      • Naito K
      • et al.
      Ultraviolet C light with wavelength of 222 nm inactivates a wide spectrum of microbial pathogens.
      • Welch D
      • Buonanno M
      • Grilj V
      • et al.
      Far-UVC light: a new tool to control the spread of airborne-mediated microbial diseases.
      • Buonanno M
      • Welch D
      • Shuryak I
      • Brenner DJ
      Far-UVC light (222 nm) efficiently and safely inactivates airborne human coronaviruses.
      For 222-nm UVC irradiation, the Care222 was placed 24 cm above the surface of the plates, and the radiation intensity at the surface of the plates was 0.1 mW/cm2, as measured with a recently calibrated Unimeter SNK005 meter (Ushio Inc., Tokyo, Japan). After irradiation for each treatment time, the control and treated plates were washed with 1 mL of phosphate-buffered saline for 1 minute and the virus-containing phosphate-buffered saline was collected in a test tube for analysis.

      TCID50

      We used the standard TCID50 method to determine virus titer for the collected viral samples from each plate as previously described.
      • Ueda K
      • Kawabata R
      • Irie T
      • Nakai Y
      • Tohya Y
      • Sakaguchi T
      Inactivation of pathogenic viruses by plant-derived tannins: strong effects of extracts from persimmon (Diospyros kaki) on a broad range of viruses.
      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.

      Quantitative reverse transcription PCR (RT-qPCR)

      SARS-CoV-2 RNA was extracted from the collected viral samples from each plate using a NucleoSpin RNA Virus kit (MACHEREY-NAGEL GmbH & Co. KG., Düren, Germany) following the manufacturer's protocol. Conventional RT-qPCR for the specific amplification of the nucleocapsid (N) gene of SARS-CoV-2 was performed using the One Step PrimeScript III RT-qPCR mix (Takara Bio Inc., Kusatsu, Japan) according to the manufacturer's protocol. The following sets of primers and probe were used: forward primer (2.4 μM), 5′-AAA TTT TGG GGA CCA GGA AC-3′; reverse primer (3.2 μM), 5′-TGG CAG CTG TGT AGG TCA AC-3′; and 0.4 μM probe, 5′-FAM-ATG TCG CGC ATT GGC ATG GA-BHQ-3′. Thermal cycling was carried out as follows: reverse transcription at 52 °C for 5 minutes, initial denaturation at 95 °C for 10 seconds, 45 cycles of denaturation at 95 °C for 5 seconds, and a final annealing/extension at 60 °C for 30 seconds.

      Results

      The results of the TCID50 assay and RT-qPCR are shown in Table 1. Three mJ/cm2 of 222 nm UVC light (0.1 mW/cm2 for 30 seconds) reduced viable SARS-CoV-2 (99.7% reduction) to undetectable levels based on the TCID50 assay. In contrast, the copy number of SARS-CoV-2 RNA did not change after UV irradiation compared to that of the nonirradiation control, even after the maximum 300 s exposure (cycle quantification (Cq), 17.02-18.32).
      Table 1Efficacy of 222-nm UVC light (0.1 mW/cm2) on reducing viable SARS-CoV-2
      UVC irradiation time
      Control10 seconds30 seconds60 seconds300 seconds
      Mean viable SARS-CoV-2 (TICD50/mL) (SD)2.05 ± 1.21 × 1042.34 ± 0.86 × 1036.32 ± 0.0 × 1016.32 ± 0.0 × 1016.32 ± 0.0 × 101
      Log reduction0.942.512.512.51
      Mean SARS-CoV-2 RNA
      SARS-CoV-2 RNA was measured by quantitative reverse transcription PCR.
      (copies/test) (SD)
      2.12 ± 0.27 × 1075.75 ± 0.82 × 1073.41 ± 1.08 × 1072.95 ± 0.41 × 1073.03 ± 1.73 × 107
      SARS-CoV-2, severe acute respiratory syndrome coronavirus 2; TCID50, 50% tissue culture infectious dose; SD, standard deviation.
      low asterisk SARS-CoV-2 RNA was measured by quantitative reverse transcription PCR.

      Discussion

      The results of this study demonstrated that 222-nm UVC irradiation at 3 mJ/cm2 (0.1 mW/cm2 for 30 seconds) resulted in a 99.7% reduction of viable SARS-CoV-2 based on the TCID50 assay. Previous reports showed that a low dose of 222-nm UV inactivated several viruses, although the treated viruses were aerosolized; 2 mJ/cm2 of 222-nm UV inactivated >95% of H1N1 aerosolized influenza virus.
      • Welch D
      • Buonanno M
      • Grilj V
      • et al.
      Far-UVC light: a new tool to control the spread of airborne-mediated microbial diseases.
      In addition, 1.7 and 1.2 mJ/cm2 of 222-nm UV inactivated 99.9% of aerosolized human coronaviruses alpha HCoV-229E and beta HCoV-OC43, respectively.
      • Buonanno M
      • Welch D
      • Shuryak I
      • Brenner DJ
      Far-UVC light (222 nm) efficiently and safely inactivates airborne human coronaviruses.
      Previous report showed that the viral titer of SARS-CoV-2 was reduced on a plastic plate over time.
      • van Doremalen N
      • Bushmaker T
      • Morris DH
      • et al.
      Aerosol and surface stability of SARS-CoV-2 as compared with SARS-CoV-1.
      The decrease of the viral titer of the control plate by dry conditions may have resulted in the plateau of the virus killing at a very low UV dose of 3 mJ/cm2. A few previous reports showed the effectiveness of UV disinfection on SARS-CoV-2
      • Simmons S
      • Carrion R
      • Alfson K
      • et al.
      Deactivation of SARS-CoV-2 with pulsed xenon ultraviolet: Implications for environmental COVID-19 control [e-pub ahead of print].
      ,
      • Heilingloh CS
      • Aufderhorst UW
      • Schipper L
      • et al.
      Susceptibility of SARS-CoV-2 to UV irradiation.
      ; however, it is difficult to compare the result of this study to that of previous studies because the wavelength of UV or the experimental conditions are different. In contrast to the viable SARS-CoV-2, the copy number of SARS-CoV-2 RNA determined by RT-qPCR was not reduced even after 30 mJ/cm2 (0.1 mW/cm2 for 300 seconds) of 222-nm UVC irradiation. Because our results of RT-qPCR showed that the almost same number of RNA copies with a range of Cq values from 17.02 to 18.32, we believe that our RT-qPCR assay worked well. Recent studies have reported on SARS-CoV-2 contamination in hospital environments as determined by RT-qPCR.
      • Wu S
      • Wang Y
      • Jin X
      • Tian J
      • Liu J
      • Mao Y
      Environmental contamination by SARS-CoV-2 in a designated hospital for coronavirus disease 2019.
      • Ong SWX
      • Tan YK
      • Chia PY
      • et al.
      Air, surface environmental, and personal protective equipment contamination by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) from a symptomatic patient.
      • Ye G
      • Lin H
      • Chen S
      • et al.
      Environmental contamination of SARS-CoV-2 in healthcare premises.
      However, our study suggests that this technique does not accurately reflect viable SARS-CoV-2 contamination. Rather, the TCID50 assay should be used to detect viable SARS-CoV-2 contamination after UV disinfection.
      To protect health care workers and to help stop the spread of SARS-CoV-2, more thorough prevention and control practices are needed. Since COVID-19 has become a pandemic and there are asymptomatic patients,
      • Mizumoto K
      • Kagaya K
      • Zarebski A
      • Chowell G
      Estimating the asymptomatic proportion of coronavirus disease 2019 (COVID-19) cases on board the Diamond Princess cruise ship, Yokohama, Japan, 2020.
      attention is being focused on environmental disinfection in public spaces beyond health care settings in which many people come into contact with various surfaces. Although the most common UV disinfection system in use is a germicidal lamp emitting around 254-nm UVC,
      • Marra AR
      • Schweizer ML
      • Edmond MB
      No-touch disinfection methods to decrease multidrug-resistant organism infections: a systematic review and meta-analysis.
      it is well known that this wavelength is harmful to the skin and eyes. Thus, the germicidal lamp UV disinfection systems can mainly only be used in unoccupied spaces. In contrast, recent studies have shown that 222-nm UVC is less harmful than 254-nm UVC because far-UVC light has a very limited penetration depth in the skin or eyes and it is also an efficient anti-microbial technology.
      • Buonanno M
      • Ponnaiya B
      • Welch D
      • et al.
      Germicidal efficacy and mammalian skin safety of 222-nm UV light.
      • Narita K
      • Asano K
      • Morimoto Y
      • et al.
      Disinfection and healing effects of 222-nm UVC light on methicillin-resistant Staphylococcus aureus infection in mouse wounds.
      • Narita K
      • Asano K
      • Morimoto Y
      • Igarashi T
      • Nakane A
      Chronic irradiation with 222-nm UVC light induces neither DNA damage nor epidermal lesions in mouse skin, even at high doses.
      • Yamano N
      • Kunisada M
      • Kaidzu S
      • et al.
      Long-term effects of 222-nm ultraviolet radiation C sterilizing lamps on mice susceptible to ultraviolet radiation.
      • Narita K
      • Asano K
      • Naito K
      • et al.
      Ultraviolet C light with wavelength of 222 nm inactivates a wide spectrum of microbial pathogens.
      Therefore, a 222-nm UVC disinfection system could be used in occupied public spaces including a hospital room, which is occupied by patients and frequented by health care workers and possibly, visitors. However, further study about the safety and efficacy of 222-nm UVC irradiation in occupied space is needed.
      One limitation of our study is that we only investigated the in vitro efficacy of 222-nm UV irradiation on SARS-CoV-2 contamination. We did not evaluate this technology in a real-world setting, such as a surface counter-top.

      Conclusions

      In conclusion, our study demonstrated the effectiveness of 222-nm UVC irradiation on viable SARS-CoV-2. Our results suggest that this technology could be used for infection prevention and control against COVID-19, not only in unoccupied spaces but also occupied spaces. Further evaluation of the safety and efficacy of 222-nm UVC irradiation in reducing the contamination of real-world surfaces and the transmission of SARS-CoV-2 is needed.

      Acknowledgment

      We would like to thank Editage (www.editage.com) for English language editing.

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