Effectiveness of UV-C treatment on Corona Virus A - Summary

Effectiveness of UV-C treatment on Corona virus – A Summary
Based on -
Inactivation of Viruses on Surfaces by Ultraviolet Germicidal Irradiation
Journal of Occupational and Environmental Hygiene
Volume 4, 2007 – Issue 6
Chun-Chieh Tseng & Chih-Shan Li
Pages 400-405 | Published online: 07 Nov 2007

Viruses are obligate parasites that cannot multiply or propagate outside a host cell. Inanimate surfaces can be contaminated with viruses on contact with infectious body fluids or the settling of airborne viral particles. For surfaces to serve as sources of viral disease, the involved virus must survive in association with the surface until it encounters a susceptible host. There have been a number of viral outbreaks related to surface-related transmission, such as hepatitis virus, rotavirus, enterovirus, and severe acute respiratory syndrome coronavirus (SARS CoV). In many outbreaks caused by viruses, the transmission of the agents can occur through contaminated surfaces. To combat infectious disease outbreaks caused by these viruses, we need to evaluate engineering control methods for inactivation of viruses on surfaces. Ultraviolet germicidal irradiation (UVGI) is a very promising method to do that.

UVGI is increasingly becoming most effective method for preventing spread of devastating infections from contaminated surfaces, both in the healthcare environmental and outside. Microorganisms are uniquely vulnerable to ultraviolet energy in wavelengths between 200 to 280 nanometres (nm), also known as ultraviolet C (UV-C). On exposure to UVC, the nucleic acid sequence of microorganisms forms pyrimidine dimers, that interfere with their replication and render them non-infectious.

The purpose of this study referred to here was to determine the effectiveness of UVCGI for virus inactivation on surfaces. It is believed that UV-C radiation would restructure the nucleic acid of the microorganisms and destroy its replication ability; therefore, the type of the viral nucleic acid may play a critical role on virus inactivation by UVCGI. The effects of UV dose, type of virus nucleic acid, and RH on the effectiveness of UVGI to inactivate surface viruses were evaluated in a UV exposure chamber.

Viruses used in this study are divided into four groups viz: single-stranded RNA (ssRNA), singlestranded DNA (ssDNA), double-stranded RNA (dsRNA), and double-stranded DNA (dsDNA). Bacteriophages are more resistant to UVGI than other pathogenic viruses; therefore, they are considered as suitable indicators. The bacteriophages used in this study have been used as indicators of poliovirus (MS2), enterovirus (phi X174), enveloped viruses (phi 6), and human immunodeficiency virus (T7). Consequently, this study evaluates effective of UVC dose for various nucleic acid type of bacteriophage viruses. The study was enabled with grant from National Science Council, Republic of China.

It should be noted here that Corona virus, including the COVID-19 strain is a form of virus with ssRNA (single stranded). MS2 Bacteriophage with ssRNA was studied in detail as one of the four types of viruses subjected to UVCGI dosage in two humidity conditions, viz. 55% and 85%. The amount of UV-C dosage required to reduce 90% and 99% viral load of each type was determined, and compared to one another to get a better understanding of the effectiveness of UV-C dosage on viral reduction of each type on surface of gelatine based medium.

It was observed that viruses on a surface with single-stranded nucleic acid (ssRNA and ssDNA) were more susceptible to UV-C inactivation than viruses with double-stranded nucleic acid, because the complex nucleic acids (doubled strained genomes) of both dsRNA and dsDNA could enable the two types of phages tested to use the host enzymes to repair damages. In addition, the bacteriophages are more resistant to UVGI than other pathogenic viruses in the environment. For 99% viral reduction, the UV dose for MS2 (ssRNA) ranged from 2.51 to 6.50 mJ/cm2, for phi X174 (ssDNA) from 5.04 to 8.34 mJ/cm2, for ph 6 (dsRNA) from 7.75 to 10.57 mJ/cm2, and for T7 (dsDNA) from 15.54 to 16.20 mJ/cm2. For the same viral reduction, the UV dose at 85% relative humidity (RH) was higher than that at 55% RH. The susceptibility factor for the viruses was higher at 55% RH than at 85% RH possibly because when RH increases, water sorption onto the virus surface might provide protection against UV-induced DNA or RNA damage.

In summary, results showed that UVCGI was a very effective method for inactivation of viruses on surfaces. The effectiveness of UVCGI for virus inactivation on surfaces was found to fit well with an exponential decay model. Moreover, observations are in agreement with the BunsenRoscoe reciprocity law that states if a photobiologic effect depends purely on photochemical events, the biologic effect of a UVC exposure depends on the product of the irradiance and exposure time (total dose). Hence, the UVCGI effects for virus inactivation on surface depended on UVC dose and percent RH. For all nucleic acid types of virus, the survival fraction decreased exponentially at higher UV dose.

As a side note, in comparison with airborne virus evaluation studies conducted earlier, it was demonstrated that UVC lethal radiation doses required for airborne viruses were lower than those for viruses on surfaces. Furthermore, the ratio of the 90% viral reduction dose for virus on surfaces to airborne viruses ranged from 3.9 to 7.6 for MS2, from 5.6 to 9.0 for phi X174, from 5.7 to 6.2 for phi 6, and from 6.8 to 8.5 for T7. This may be explained by the fact that viruses can form aggregation on surfaces. When compared with studies where UVGI effectiveness was investigated on viruses in suspension, much higher UV doses were needed for 90% inactivation of MS2 virus (12–24 mJ/cm2) than on a surface (1.32 to 3.2 mJ/cm2). Viruses may be less susceptible to UVGI when associated with water.

(Disclaimer: Please note that the above study was not conducted on Cornona Virus. MS2, a virus with similar nucleic acid genome ‘ssRNA’ was studied. As UV-C light acts on the nucleic acid structure on microorganisms, the effect of UV-C on ssRNA can be extended to other viruses with genome similar to MS2, like the Corona virus family, other environmental factors remaining constant.) For access to the full Study, please visit the following URL: https://www.tandfonline.com/doi/full/10.1080/15459620701329012