skip to main content


Title: Systematic evaluating and modeling of SARS-CoV-2 UVC disinfection
Abstract The ongoing COVID-19 global pandemic has necessitated evaluating various disinfection technologies for reducing viral transmission in public settings. Ultraviolet (UV) radiation can inactivate pathogens and viruses but more insight is needed into the performance of different UV wavelengths and their applications. We observed greater than a 3-log reduction of SARS-CoV-2 infectivity with a dose of 12.5 mJ/cm 2 of 254 nm UV light when the viruses were suspended in PBS, while a dose of 25 mJ/cm 2 was necessary to achieve a similar reduction when they were in an EMEM culture medium containing 2%(v/v) FBS, highlighting the critical effect of media in which the virus is suspended, given that SARS-CoV-2 is always aerosolized when airborne or deposited on a surface. It was found that SARS-CoV-2 susceptibility (a measure of the effectiveness of the UV light) in a buffer such as PBS was 4.4-fold greater than that in a cell culture medium. Furthermore, we discovered the attenuation of UVC disinfection by amino acids, vitamins, and niacinamide, highlighting the importance of determining UVC dosages under a condition close to aerosols that wrap the viruses. We developed a disinfection model to determine the effect of the environment on UVC effectiveness with three different wavelengths, 222 nm, 254 nm, and 265 nm. An inverse correlation between the liquid absorbance and the viral susceptibility was observed. We found that 222 nm light was most effective at reducing viral infectivity in low absorbing liquids such as PBS, whereas 265 nm light was most effective in high absorbing liquids such as cell culture medium. Viral susceptibility was further decreased in N95 masks with 222 nm light being the most effective. The safety of 222 nm was also studied. We detected changes to the mechanical properties of the stratum corneum of human skins when the 222 nm accumulative exposure exceeded 50 J/cm 2 .The findings highlight the need to evaluate each UV for a given application, as well as limiting the dose to the lowest dose necessary to avoid unnecessary exposure to the public.  more » « less
Award ID(s):
2031223
NSF-PAR ID:
10338918
Author(s) / Creator(s):
; ; ; ; ;
Date Published:
Journal Name:
Scientific Reports
Volume:
12
Issue:
1
ISSN:
2045-2322
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Dudley, Edward G. (Ed.)
    ABSTRACT Effective disinfection technology to combat severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) can help reduce viral transmission during the ongoing COVID-19 global pandemic and in the future. UV devices emitting UVC irradiation (200 to 280 nm) have proven to be effective for virus disinfection, but limited information is available for SARS-CoV-2 due to the safety requirements of testing, which is limited to biosafety level 3 (BSL3) laboratories. In this study, inactivation of SARS-CoV-2 in thin-film buffered aqueous solution (pH 7.4) was determined across UVC irradiation wavelengths of 222 to 282 nm from krypton chloride (KrCl*) excimers, a low-pressure mercury-vapor lamp, and two UVC light-emitting diodes. Our results show that all tested UVC devices can effectively inactivate SARS-CoV-2, among which the KrCl* excimer had the best disinfection performance (i.e., highest inactivation rate). The inactivation rate constants of SARS-CoV-2 across wavelengths are similar to those for murine hepatitis virus (MHV) from our previous investigation, suggesting that MHV can serve as a reliable surrogate of SARS-CoV-2 with a lower BSL requirement (BSL2) during UV disinfection tests. This study provides fundamental information on UVC’s action on SARS-CoV-2 and guidance for achieving reliable disinfection performance with UVC devices. IMPORTANCE UV light is an effective tool to help stem the spread of respiratory viruses and protect public health in commercial, public, transportation, and health care settings. For effective use of UV, there is a need to determine the efficiency of different UV wavelengths in killing pathogens, specifically SARS-CoV-2, to support efforts to control the ongoing COVID-19 global pandemic and future coronavirus-caused respiratory virus pandemics. We found that SARS-CoV-2 can be inactivated effectively using a broad range of UVC wavelengths, and 222 nm provided the best disinfection performance. Interestingly, 222-nm irradiation has been found to be safe for human exposure up to thresholds that are beyond those effective for inactivating viruses. Therefore, applying UV light from KrCl* excimers in public spaces can effectively help reduce viral aerosol or surface-based transmissions. 
    more » « less
  2. After decades of UV disinfection practice and numerous studies on the potential for pathogens to undergo dark or photo-repair after UV exposure, recent advances in UV light emitting diode (LED) technologies prompt renewed attention to bacterial reactivation and regrowth processes after UV exposure. The aspect of photorepair conditions warrants particular attention, because even studies on conventional mercury vapor lamps have not sufficiently characterized these parameters. Wastewater encounters a wide range of environmental conditions upon discharge ( e.g. , solar irradiation and dissolved organics) which may affect repair processes and ultimately lead to overestimations of pathogen removal. Escherichia coli was used here to investigate the impacts of changing reactivation conditions after UV 254 and UV 278 irradiation. UV 254 and UV 278 doses of 13.75 ± 0.4 mJ cm −2 and 28.3 ± 0.8 mJ cm −2 were required to induce a 3.0 log inactivation of E. coli , respectively. Specifically, photoreactivation conditions were varied across dissolved organic matter (DOM) content and photoreactivation wavelengths and intensities. Photoreactivation achieved higher log recoveries than dark repair, ranging from 0.8 to 1.8 log differences, but a secondary disinfection effect occurred under UVA irradiation. During photoreactivation, humic acid inhibited the initial repair of UV 278 -dosed E. coli , but culture media enhanced recovery for both dosage wavelengths. Photoreactivation profiles under UV 395 , UV 365 , and visible light depended on both fluence and time, with more regrowth observed upon exposure to visible light and the least under 365 nm. The susceptibility of E. coli to UVA was increased by prior exposure to UVC. 
    more » « less
  3. null (Ed.)
    Ultraviolet (UV) devices emitting UVC irradiation (200− 280 nm) have proven to be effective for virus disinfection, especially on surfaces and in air, due to their rapid effectiveness and limited to no material corrosion. Numerous studies of UV-induced inactivation focused on nonenveloped viruses. Little is known about UVC action on enveloped viruses across UVC wavelengths. In this study, we determined inactivation efficiencies of two coronaviruses (ssRNA) and an enveloped dsRNA bacteriophage surrogate in buffered aqueous solution (pH 7.4) using five commonly available UVC devices that uniquely emit light at different wavelengths spanning 222 nm emitting krypton chloride (KrCl*) excimers to 282 nm emitting UVC LEDs. Our results show that enveloped viruses can be effectively inactivated using UVC devices, among which the KrCl* excimer had the best disinfection performance (i.e., highest inactivation rate) for all three enveloped viruses. The coronaviruses exhibited similar sensitivities to UV irradiation across the UVC range, whereas the bacteriophage surrogate was much more resistant and exhibited significantly higher sensitivity to the Far UVC (<230 nm) irradiation. This study provides necessary information and guidance for using UVC devices for enveloped virus disinfection, which may help control virus transmission in public spaces during the ongoing COVID-19 pandemic and beyond. 
    more » « less
  4. null (Ed.)
    To better understand the elimination of transforming activity of antibiotic resistance genes (ARGs), this study investigated the deactivation of transforming activity of an ARG (in Escherichia coli as a host) and ARG degradation (according to quantitative PCR [qPCR] with different amplicon sizes) during UV (254 nm) and UV/H 2 O 2 treatments of plasmid pUC19 containing an ampicillin resistance gene ( amp R ). The required UV fluence for each log 10 reduction of the transforming activity during UV treatment was ∼37 mJ cm −2 for both extra- and intra-cellular pUC19 (the latter within E. coli ). The resulting fluence-based rate constant ( k ) of ∼6.2 × 10 −2 cm 2 mJ −1 was comparable to the k determined previously for transforming activity loss of plasmids using host cells capable of DNA repair, but much lower (∼10-fold) than that for DNA repair-deficient cells. The k value for pUC19 transforming activity loss was similarly much lower than the k calculated for cyclobutane-pyrimidine dimer (CPD) formation in the entire plasmid. These results indicate the significant role of CPD repair in the host cells. The degradation rate constants ( k ) of amp R measured by qPCR increased with increasing target amplicon size (192–851 bp) and were close to the k calculated for the CPD formation in the given amplicons. Further analysis of the degradation kinetics of plasmid-encoded genes from this study and from the literature revealed that qPCR detected most UV-induced DNA damage. In the extracellular plasmid, DNA damage mechanisms other than CPD formation ( e.g. , base oxidation) were detectable by qPCR and gel electrophoresis, especially during UV/H 2 O 2 treatment. Nevertheless, the enhanced DNA damage for the extracellular plasmids did not result in faster elimination of the transforming activity. Our results indicate that calculated CPD formation rates and qPCR analyses are useful for predicting and/or measuring the rate of DNA damage and predicting the efficiency of transforming activity elimination for plasmid-encoded ARGs during UV-based water disinfection and oxidation processes. 
    more » « less
  5. Abstract

    Ultraviolet germicidal irradiation (UVGI) and ozone disinfection are crucial methods for mitigating the airborne transmission of pathogenic microorganisms in high-risk settings, particularly with the emergence of respiratory viral pathogens such as SARS-CoV-2 and avian influenza viruses. This study quantitatively investigates the influence of UVGI and ozone on the viability ofE. coliin bioaerosols, with a particular focus on howE. coliviability depends on the size of the bioaerosols, a critical factor that determines deposition patterns within the human respiratory system and the evolution of bioaerosols in indoor environments. This study used a controlled small-scale laboratory chamber whereE. colisuspensions were aerosolized and subjected to varying levels of UVGI and ozone levels throughout the exposure time (2–6 s). The normalized viability ofE. coliwas found to be significantly reduced by UVGI (60–240μW s cm−2) as the exposure time increased from 2 to 6 s, and the most substantial reduction ofE. colinormalized viability was observed when UVGI and ozone (65–131 ppb) were used in combination. We also found that UVGI reduced the normalized viability ofE. coliin bioaerosols more significantly with smaller sizes (0.25–0.5μm) than with larger sizes (0.5–2.5μm). However, when combining UVGI and ozone, the normalized viability was higher for smaller particle sizes than for the larger ones. The findings provide insights into the development of effective UVGI disinfection engineering methods to control the spread of pathogenic microorganisms in high-risk environments. By understanding the influence of the viability of microorganisms in various bioaerosol sizes, we can optimize UVGI and ozone techniques to reduce the potential risk of airborne transmission of pathogens.

     
    more » « less