Far-UVC light: A Promising Technology to Reduce the Spread of Airborne-Mediated Microbial Diseases

Several laboratories worldwide have been studying the anti-microbial efficacy of far-UVC light and its safety for human tissues (1, 2). Here it is described mainly the work done on the topic to date by our team at Columbia University in New York.

The use of ultraviolet light for sterilization purposes is well established (3). However, its use where humans are present is limited by the fact that conventional germicidal lamps, principally emitting at 254 nm, induce skin cancer and long-term eye damage like cataracts (4, 5). In contrast, we have shown that light in the range of 207-222 nm (far-UVC) efficiently kills bacteria on surfaces and viruses in aerosol while being apparently safe for human skin and eyes.

The biophysical explanation is based on the limited penetration distance of far-UVC light in biological samples. Specifically, while far-UVC light has enough range to traverse microbes that are much smaller in size than human cells (less than 1 μm in diameter, compared to the diameter of typical human cells ranging from about 10–25 μm), it is strongly absorbed by the proteins in the cytoplasm of human cells and is drastically attenuated before reaching the human cell nucleus. It follows that far-UVC light is not able to penetrate the stratum corneum of skin (i.e. the dead skin layer) and reach the underlying critical basal cells or melanocytes. Prompt absorbance into the tear layer makes far-UVC light in principle safe for the eyes.

The two main purposes of our far-UVC studies are (1) the safety for human skin and eyes, and (2) anti-microbial efficacy.

We have shown that compared to 254 nm light, far-UVC light does not kill human cells in vitro, does not induce damage in 3-dimensional human skin models, and does not damage mouse skin exposed to a cumulative dose of ~160 mJ/cm² delivered in a 7-hour period (6-9). Ongoing studies are aimed at assessing long-term skin and eye damage in mice exposed to 222-nm light for 8 hours a day, five days a week, for 60 weeks.

Regarding anti-microbial efficacy of far-UVC light, we have observed efficient killing of bacteria on surfaces (e.g. methicillin-resistant Staphylococcus aureus (MRSA), Staphylococcus epidermidis, Pseudomonas aeruginosa) (6, 8, 9) and efficient killing of viruses in aerosol such as influenza A (H1N1) (10). Recently, we have extended the virus studies to human coronaviruses of both genera alpha (HCoV-229E) and beta (HCoV-OC43) (11).

Transmission of SARS-CoV-2, the beta coronavirus causing COVID-19, can occur via airborne routes; SARS-CoV-2 remains viable in aerosols for up to 16 hours (12, 13), and can be spread by asymptomatic carriers even through speech droplets carrying the virus, which can linger in the air for 14 minutes (14).

Using a custom-made aerosol chamber, we have shown that 1.7 mJ/cm² or 1.2 mJ/cm² of 222 nm light produced 99.9% (3-log) reduction of aerosolized alpha HCoV-229E or beta HCoV-OC43, respectively (9). As all human coronaviruses have similar genomic size, a key determinant of radiation sensitivity, it is realistic to expect that far-UVC light will show comparable inactivation efficiency against other human coronaviruses, including SARS-CoV-2. Our ongoing studies are investigating far-UVC mediated killing of SARS-CoV-2 on different surfaces; future studies will explore its killing when exposed in aerosol to 222-nm light.

The applications of far-UVC technology for sterilization purposes is vast; for instance, continuous exposure of the wound to far-UVC light during surgery or any dental procedure may inactivate the microbes alighting directly onto the surgical wound from the air. If proven to be safe to eyes as well as skin, continuous operation of far-UVC light would not require the use of cumbersome protective clothing, hoods and eye shields for the surgical staff and the patient. Moreover, the killing of airborne pathogens within a short time of their production would considerably reduce their transmission, thereby limiting seasonal influenza epidemics, transmission of measles and tuberculosis, as well as future pandemics.

Low dose rate far-UVC lights may be used in highly occupied indoor public locations such as hospitals, transportation vehicles, airports and schools, potentially representing a safe and inexpensive tool to reduce the spread of airborne-mediated microbial diseases.

Questions from the editor:

1. Rajeev Chitguppi: How early and at what stage are we currently in our journey towards seeing far UVC lights installed in every dental clinic? We do not have any units available in the market yet.

   Dr Buonanno: Although I mainly deal with research, we have collaborated in the past with two UV light manufacturers, Ushio and Edan Park. They both advertise 222nm products
   a. https://www.ushio.com/product/care222-mercury-free-far-uv-c-excimer/
   b. https://www.edenpark.com/products.html
   but I am not sure how their FDA/EPA (Food and Drug Administration/ Environmental Protection Agency) approvals are going, so I do not know how long it would be before far-UVC light will be produced on a large scale.

2. Rajeev Chitguppi: Until far-UVC lights become the mainstay, should we continue to use the conventional UVC (254 nm) by taking all due precautions like moving out of the room while the lights are on?

   Dr Buonanno: You are absolutely right. Until that time dentists using standard germicidal lamps (e.g. 254 nm) in their practice should continue to do so by taking all the necessary precautions to avoid skin and eye exposure, that is leaving the room when those lamps are on or wear protective gowns and goggles/ face shields to protect skin and eye if they need to be in the room.

References cited

1. Taylor W, et al. DNA Damage Kills Bacterial Spores and Cells Exposed to 222-Nanometer UV Radiation. Appl Environ Microbiol. 2020;86(8):e03039-19. doi:10.1128/AEM.03039-19.
2. Narita, K. et al. Disinfection and healing effects of 222-nm UVC light on methicillin-resistant Staphylococcus aureus infection in mouse wounds. J Photochem Photobiol B 178, 10-18, doi:https://doi.org/10.1016/j.jphotobiol.2017.10.030 (2018)
3. Kowalski, W. J. Ultraviolet Germicidal Irradiation Handbook: UVGI for Air and Surface Disinfection. New York: Springer, 2009.
4. Setlow, R. B., et al. Wavelengths effective in induction of malignant melanoma. Proc Natl Acad Sci U S A 90, 6666-6670 (1993).
5. Balasubramanian, D. Ultraviolet radiation and cataract. J Ocul Pharmacol Ther 16, 285-297, doi:10.1089/jop.2000.16.285 (2000).
6. Buonanno, M. et al. 207-nm UV Light - A Promising Tool for Safe Low-Cost Reduction of Surgical Site Infections. I: In Vitro Studies. PLoS One 8, e76968, doi:10.1371/journal.pone.0076968 (2013).
7. Buonanno, M. et al. 207-nm UV Light-A Promising Tool for Safe Low-Cost Reduction of Surgical Site Infections. II: In-Vivo Safety Studies. PLoS One 11, e0138418, doi:10.1371/journal.pone.0138418 PONE-D-15-32644 [pii] (2016).
8. Buonanno, M. et al. Germicidal Efficacy and Mammalian Skin Safety of 222-nm UV Light. Radiation Research 187, 483-491, doi:10.1667/RR0010CC.1 (2017).
9. Ponnaiya, B. et al. Far-UVC light prevents MRSA infection of superficial wounds in vivo. PLOS ONE 13, e0192053, doi:10.1371/journal.pone.0192053 (2018).
10. Welch, D. et al. Far-UVC light: A new tool to control the spread of airborne-mediated microbial diseases. Sci Rep 8, 2752, doi:10.1038/s41598-018-21058-w (2018).
11. Buonanno, M. et al. Far-UVC light efficiently and safely inactivates airborne human coronaviruses, 27 April 2020, PREPRINT (Version 1) available at Research Square [+https://doi.org/10.21203/rs.3.rs-25728/v1+]
12. van Doremalen, N. et al. Aerosol and Surface Stability of SARS-CoV-2 as Compared with SARS-CoV-1. N Engl J Med, doi:10.1056/NEJMc2004973 (2020).
13. Fears A.C. et al. 2020 Comparative dynamic aerosol efficiencies of three emergent coronaviruses and the unusual persistence of SARS-CoV-2 in aerosol suspensions medRxiv 2020.04.13.20063784; doi: https://doi.org/10.1101/2020.04.13.20063784.
14. Stadnytskyi V. et al The airborne lifetime of small speech droplets and their potential importance in SARS-CoV-2 transmission Proc Natl Acad Sci 2020, 202006874; DOI: 10.1073/pnas.2006874117

 

Author:

Manuela Buonanno is an Associate Research Scientist at the Center for Radiological Research at Columbia University in New York, USA.

She received her B.S. in Physics from the University of Naples ‘’Federico II’’ in Italy. She was then awarded a scholarship from Rutgers University (New Jersey, USA) to pursue her PhD studies on targeted and non-targeted effects induced by ionizing radiation.

In 2011, Dr Buonanno joined the Center for Radiological Research at Columbia University as a Postdoctoral Research Scientist and was then promoted to Associate Research Scientist.

Dr Buonanno investigates the antimicrobial applications of far-UVC light, including prevention of surgical site infections and viral transmission. Dr Buonanno’s studies showed that single-wavelength in the range 207-222 nm kills drug-resistant bacteria on surfaces and viruses in aerosol without apparent harm to human skin and eyes.

Other current research interests include biological effects induced by ionizing radiation. Initial works focused on effects induced by charged particle microbeam radiation in small animal models. Her current studies aim at exploiting the biophysical properties of ionizing radiation (LET, dose, dose-rate) to devise more effective radiotherapy treatments. Specifically, she studies high dose rate (FLASH) effects, and how different types of radiation (LET) stimulate the immune response.

A long-standing member of the Radiation Research Society (RRS), Dr Buonanno is the current Chair of the Education and Website Committee; since 2007 she edits and produces scientific podcasts for the RRS.

In 2016, the RRS and the University of Wisconsin awarded Dr Buonanno with the Jack Fowler Award, which recognizes outstanding junior investigators for exceptional work in the radiation sciences. Dr Buonanno is a new member of the National Council on Radiation Protection and Measurements (NCRP).

Connect:

Dr Manuela Buonanno on Researchgate

Dr Manuela Buonanno on her university page

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