Health

Ultraviolet C radiation is effective in inactivating SARS-CoV-2 on glass surfaces, a study finds

A team of scientists from the Texas Biomedical Research Institute and UV Innovators, Inc., USA, recently developed an ultraviolet C radiation emitting device called NuvaWave, which is capable of inactivating severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) on glass surfaces within seconds. The study is currently available on the bioRxiv* preprint server.

Schematic representation of the workflow. SARS-CoV-2 was placed on the chambered glass slide, dried for 1 hour at room temperature, and then exposed to UVC light radiation using the NuvaWave device for 1, 2, 4 and 8 seconds. No UVC light exposure was used as control. After UVC light exposure, virus was recovered, serial diluted and used to assess viable virus in Vero E6 cells by the plaque assay.

Background

SARS-CoV-2, the causative pathogen of coronavirus disease 2019 (COVID-19), is an enveloped RNA virus that primarily spread via respiratory droplets. However, strong evidence is now available to support the possibility of airborne transmission of SARS-CoV-2. In addition, a growing pool of evidence has suggested that surface contamination, especially in hospitals and public places, might also increase the risk of SARS-CoV-2 transmission. Thus, in addition to following pandemic-related control measures at person-level, such as wearing face masks, sanitizing hands, and maintaining physical distancing, it is important to reduce the risk of surface contamination through frequent sterilization.

Given the well-established effectiveness of ultraviolet C (UVC) radiation in eliminating pathogens from surfaces and air, the current study scientists have developed a device called NuvaWave that generates non-ionizing UVC radiation at a wavelength of 270 nm, which is sufficient for germicidal efficacy.

Study design

NuvaWave is a computer-controlled, powerful, handheld device, which is designed to disinfect surfaces with UVC radiation by moving the device over the surface from a distance of 1 to 3.5 inches. An external battery pack has been attached to the device to support up to 3 hours of use, and a computer monitoring system has been incorporated to ensure steady performance over time. The UVC radiation source of the device is instantly controlled by a simple trigger mechanism.

To examine the efficiency of this device, the scientists engineered a computer-controlled robotic test fixture with the same UVC radiation engine as NuvaWave. This robotic fixture was designed to hold a chambered glass slide containing SARS-CoV-2 samples. Specifically, the viral samples were placed on the glass slide and allowed to dry in the biosafety level 3 laboratory. Afterward, the slides were placed into the robotic test fixture and exposed to UVC radiation for 1, 2, 4, and 8 seconds. Immediately after the exposure, the viral samples were reconstituted, and viral titers were estimated by plaque assay.

A total of 32 UVC light-emitting diodes (LEDs) were used in the device. In each LED, the reflectors were designed to provide uniform distribution of radiation across an area of 4 inches X 4 inches and a depth of 1 – 3.5 inches. The radiation engine was placed 2 inches above the viral sample. Under the radiation source, the viral sample and a sensor were moved at a constant speed. The sensor was used to measure the radiation dosage. The entire setup was built with a polycarbonate surrounding to avoid any possible UV exposure.

Important observations

The exposure of SARS-CoV-2 to UVC radiation for 1 and 2 seconds caused a significant reduction in viral titer compared to the unexposed control virus. Specifically, UVC exposure for 1 and 2 seconds resulted in >2.9 log10 and >3.8 log10 reductions in viral titers, respectively. Furthermore, UVC exposures for 4 and 8 seconds caused >4.7 log10 reductions in viral titers, which was beyond the detection limit.

In general, the titers of UVC-exposed virus remained significantly lower than the titer of unexposed virus at all time points tested. Importantly, more than 99.99% reduction in viral titer was observed with the average UVC dosage of 0.05 J/cm2 250 obtained at 4 second exposure time.      

Study significance

The study describes the development and validation of a UVC radiation emitting device, NuvaWave, which shows high effectiveness in inactivating SARS-CoV-2 on glass surfaces. The UVC radiation emitted from this device has been shown to dose-dependently inactivate the virus within seconds.  

*Important Notice

bioRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

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