UV Disinfection

Ultraviolet germicidal irradiation (UVGI) inactivates pathogens by damaging genomic material. Ultraviolet Germicidal Irradiation (UVGI) is electromagnetic radiation that can destroy the ability of microorganisms to reproduce by causing photochemical changes in nucleic acids.  UVGI has been widely applied for air, water, and surface decontamination.

Recently UVGI has been identified by the Centers for Disease Control (CDC) as one of the most promising methods for N95 filtering facepiece respirator (N95 FFR) decontamination, and a workflow for UVGI-based decontamination was successfully implemented at the University of Nebraska Medical Center (UNMC), among other locations.

Pathogen inactivation depends critically on ultraviolet (UV) wavelength (peak inactivation efficacy with ~260 nm UV-C light) and dose.

 

References :

  • - Kowalski, W. 2009. Ultraviolet Germicidal Irradiation Handbook: UVGI for Air and Surface Disinfection. Springer

  • - N95DECON (https://www.n95decon.org/uvc)

  • - Center for Disease Control (CDC) : https://www.cdc.gov/nceh/features/uv-radiation-safety/index.html

UVGI mode of action & appropriate dosing

UVGI inactivates pathogens primarily by damaging DNA and RNA (max UV absorption at 260 nm) (Kowalski, 2009 ).

Decontamination is critically dependent on application of the appropriate UV wavelength (UV-C, with high efficacy near 260 nm ( EPA, 2006 )) and dose (≥ 1.0 J/cm² for inactivation of SARS-CoV-2 analogues in N95 FFRs)

 

From : Stérilisation à froid du vin e du moût par les rayons ultra violets (https://www.vignevin-occitanie.com)

References :

  • - Kowalski, W. 2009.  Ultraviolet Germicidal irradiation Handbook: UVGI for Air and Surface Disinfection.  Springer

  • - N95DECON (https://www.n95decon.org/uvc)

UVGI : decontamination and reuse of filtering facepiece respirators

From Lowe JL et al - N95 filtering facepiece respirator ultraviolet germicidal irradiation process for decontaminaton and reuse

 

 

The ongoing pandemic of SARS-CoV-2 resulting in COVID-19 has severely stressed the worldwide healthcare system and has created dangerous shortages of personal protective equipment (PPE) including N95 filtering facepiece respirators (N95 FFRs). In an effort to extend the stockpile of N95 FFRs at our institution and reduce risks associated with reuse of untreated, contaminated N95 FFRs, Lowe J et al (2020) developed a surface decontamination procedure involving the delivery of ultraviolet germicidal irradiation (UVGI) to used N95 FFRs. The evidence base supporting this program includes:

 

  1. 1. UVGI has been shown to effectively inactivate a wide range of human pathogens including coronaviruses and other human respiratory viruses;
  2. 2. UVGI has been demonstrated to inactivate human respiratory viruses, including coronaviruses, on various models of N95 FFRs;
  3. 3. Levels of UVGI needed to inactive human respiratory viruses are well below the level of irradiation that adversely affects the fit and filtration characteristics of N95 FFRs; and
  4. 4. UVGI can be safely administered when appropriate safeguards are in place.

 

Any organization considering a decontamination strategy (including UVGI, etc.) to deal with lack of supply or potential lack of N95 FFR should validate their own procedures, including desired surrogate microbial reduction and retained filter efficiency and fit.

 

References :

  • - Fisher, E. M., & Shaffer, R. E. (2011). A method to determine the available UV-C dose for the decontamination of filtering facepiece respirators. Journal of Applied Microbiology , 110 (1), 287–295. https://doi.org/ 10.1111/j.1365-2672.2010.04881.x

  • - Lowe JL et al - N95 filtering facepiece respirator ultraviolet germicidal irradiation process for decontaminaton and reuse (https://www.nebraskamed.com/sites/default/files/documents/covid-19/n-95-decon-process.pdf)

How is UV disinfection used today?

It’s been known for more than 100 years that UV light kills microorganisms quite effectively. That includes viruses similar to the one that causes COVID-19. It’s widely used in wastewater and drinking water treatment, and the industry is very well regulated based on decades of science and practice. The application of UV treatment in medical care is more recent, and that’s where a lot of the research effort is going on today. Often, it’s mentioned in the context of superbugs, which are pathogens that have become resistant to traditional antibiotics.

Ron Hofmann

Professor in the department of civil and mineral engineering

So hospitals already have this technology?

Some do, but it’s a mix of different devices: some are stationary lamps and others are mobile or robotic. In a lot of cases, it’s working very well. But this application is not as mature as with water treatment and as a result there are fewer standards and regulations. Like any disinfectant, it’s the dose that matters, and a lot of engineering work goes into ensuring that whatever device you’re using actually applies enough UV light to ensure that the resulting surface is safe.

Ron Hofmann

Professor in the department of civil and mineral engineering

How does all this relate to COVID-19?

Hospitals are now having to reuse equipment that was never intended to be reused. It needs to be disinfected somehow. UV treatment can work in theory, but it depends on whether or not it is actually being applied properly. For example, if you put a bunch of coronavirus particles on a flat surface, a fairly economical dose of UV will kill almost all of those virus particles. But that’s an ideal case. Gowns or masks will have hidden crevices and folds where the UV light can’t get in. That scenario hasn’t been well studied. The other issue is that repeated exposure to UV, alone or in combination with chemical disinfectants, can wear out the rubber seals that enable the mask to work properly. Right now, we don’t know how many times you can disinfect and reuse a mask before you destroy its integrity. There are also risks associated with improper use of UV equipment. Remember, this is the same stuff that causes sunburns and skin cancer, but in a much more concentrated form. It can damage skin and it can damage eyes. The devices have to be used safely, with personnel kept well away and appropriate precautions taken.

Ron Hofmann

Professor in the department of civil and mineral engineering

Should hospitals use UV treatment to disinfect PPE?

The bottom line is that some treatment is better than no treatment. In the absence of anything else, if a hospital needs to disinfect its PPE and has one of these UV devices, by all means they should use it. Ideally, UV treatment would be one step in a multi-barrier approach. That means using it in concert with other disinfection techniques, such as hydrogen peroxide treatment. That would minimize the chances that a virus particle could hide in a crevice. It’s worth pointing out that some hospitals are running out of chemical disinfectants. The nice thing about UV treatment is that it’s there as long as you have electricity.

Ron Hofmann

Professor in the department of civil and mineral engineering