The effectiveness of UR GUV devices against aerosolized SARS-CoV-2

In a recently published study bioRxiv* Preprint servers evaluated researchers real-time inactivation of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) with ultraviolet-C.

background

As a result of many waves of outbreaks, the 2019 coronavirus disease (COVID-19) pandemic has severely impacted human health, societies and healthcare systems worldwide. The introduction of more contagious SARS-CoV-2 variants and COVID-19-related long-term health problems continue to negatively impact the global economy and public health, although vaccination and public health precautions have significantly reduced the risk of serious illness from COVID-19 -Results.

An infection prevention technique known as upper space germicidal ultraviolet-C irradiation (UR GUV), first used to inactivate jets of air Mycobacterium tuberculosis, has since been widely used during COVID-19. Despite significant scientific advances in this area, there are still concerns about the practical effectiveness of UR GUV lights as there is currently no recognized Environmental Protection Agency (EPA) technique for evaluating the effectiveness of UV-C against airborne infections.

About the study

In this study, a patient room-sized chamber was used to test the effectiveness of UR-GUV devices against large amounts of live viral aerosols. SARS-CoV-2 was used as the challenge organism.

In accordance with Biosafety Level 3 (BSL3) requirements, testing was conducted in a sealed chamber measuring 20ft x 8ft x 8ft. The overall dimensions of the test chamber generated an air displacement volume of approximately 36,245.56 liters, exceeding the EPA recommended room size and simulating real-world testing of disinfection systems against aerosolized bacteria. In the center of the 20-foot wall was a nebulization port that protruded 24 inches from the wall and was coupled to a programmable compressor system.

Four air sampling probes were installed in the room; Each placed six feet off the chamber floor and in the center of the room. Mounted in the center of one of the 8-foot-tall walls, about 6.5 feet off the ground, was a UR-GUV device containing 48 light-emitting diodes emitted by the light source.

A bluestone atomization module (BLAM) with preset pounds per square inch (PSI) along with a computer controlled liquid dispensing system was analyzed for average particle size distribution to produce bioaerosol. The team placed 7.04 x 10⁶ mean tissue culture infectious dose (TCID50)/mL of SARS-CoV-2 in a viral suspension medium in the nebulizer and untreated local atmospheric air was nebulized at a flow rate of 1 mL/min. The remaining volume of viral stock in the nebulizer was weighed after nebulization to ensure approximately the same volume was nebulized for each of the three replicate runs. Four air sampling probes, each connected to a calibrated Gilian 10i vacuum device and set to a standard flow of 5.02 L/min with a tolerance of 0.20%, were used to sample bioaerosol at zero, five, 15 and 30 minutes collect.

For each time point, sample withdrawal volumes were set at 10 minute withdrawals, allowing for a collection of approximately 50 liters of air per sampling port. Air sampling was limited to ten minute intervals. To calculate an average across the four sampling sites, all sample slices were combined into a single collection tube. The UR-GUV device was then operated in the same manner with appropriate time points and collection rates after the control runs. Virus suspensions of treated and control disks were measured using the TCID50 approach.

Results

The study results showed that the control showed significant recovery after a natural reduction in viability of aerosolized SARS-CoV-2 for 30 minutes in the chamber under controlled conditions. After five minutes of instrument operation, the initial concentration is 7.04 x 10⁶ TCID50/ml for three tests against SARS-CoV-2 has been reduced to 4.55 x 10⁶4.72×10⁶and 4.25×10⁶ TCID50/ml, on average about 4.51 x 10⁶ TCID50/ml.

The device reduced the collected SARS-CoV-2 to 1.25 x 10 after 15 minutes⁶9.86×10⁵and 7.47×10⁵with an average of about 9.93 x 10⁵ TCID50/ml. About 30 minutes later, the collected SARS-CoV-2 reduced to 4.80 x 10²1.20×10²and 1.20×10²Average 2.40 x 10² TCID50/ml.

Conclusion

Overall, study results demonstrated a robust aerosol testing protocol that demonstrated the tested device was highly effective against airborne SARS-CoV-2. Researchers believe this study protocol can be used as a reference by manufacturers and infection prevention professionals to evaluate the effectiveness of other UR-GUV technologies.