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Evaluating efficacy of UVC light for inactivation of SARS-CoV-2, MS2, and Phi6 on surfaces
Citation:
Oudejans, L., K. Ratliff, W. Calfee, W. Richter, M. Sunderman, D. Aslett, A. Abdel-Hady, M. Monge, B. Ficenec, N. Madanat, AND C. Amaral. Evaluating efficacy of UVC light for inactivation of SARS-CoV-2, MS2, and Phi6 on surfaces. To be Presented at World Microbe Forum, N/A, Virtual, June 20 - 24, 2021.
Impact/Purpose:
SARS-CoV-2, the causative virus of the CoVID-19 pandemic, is by now a highly studied pathogen, yet consensus is lacking on the effective dose to inactivate/kill this virus on surfaces using UVC light. Dose-response curves are lacking for this virus as well as many surrogates. Information of what doses can be realistically achieved in e.g., a metro car or bus to achieve disinfection are also lacking. This poster summarizes the results of lab studies on the inactivation of UVC light against SARS-CoV-2 and a surrogate virus as well as results from a field study in collaboration with LA Metro that measured UVC doses at various locations in a metro car outfitted with UVC light generated devices. This information provides a first guidance on the ability of UVC light to inactivate SARS-CoV-2 and an assessment of the possible SARS-CoV-2 surrogates for UVC disinfection research. These results are of high relevancy to researchers, companies that work on UVC implementation, transportation authorities, and other entities including the general public that may consider UVC light disinfection as a mode of disinfection of their spaces.
Description:
Motivated by the COVID-19 pandemic, the United States Environmental Protection Agency (EPA) is conducting research to evaluate the efficacy of devices to inactivate SARS-CoV-2 on surfaces in addition or as an alternative to chemical-based disinfectants. Devices that emit ultraviolet-C (UVC) light can offer some advantages over liquid disinfectant products in that they do not leave a chemical residue, and they can be conveniently applied for disinfecting liquids, solid surfaces, and contaminated air. Thus, there has been a growing interest in employing UVC devices to augment routine cleaning and disinfection practices, particularly for high-contact surfaces and in complex settings (e.g., public transportation). Partnering with large transit agencies, EPA has been evaluating the efficacy of different UVC devices, including a broad-spectrum pulsed xenon light and a continuous UVC light-emitting diode (LED), against SARS-CoV-2 and bacteriophages MS2 and Phi6 as potential surrogate viruses. SARS-CoV-2 experiments were conducted with virus inoculated in either cell culture media or simulated saliva onto 301 stainless steel, ABS plastic, and bus seat fabric, and then either immediately exposed to UVC light (with wet inoculum) or after the inoculum had dried. A range of dose conditions were evaluated by changing the distance between the light and the surfaces and the time of exposure. Additional experimental conditions were evaluated using MS2 and Phi6, including other dose conditions, impact on disinfection of inoculum applied as a droplet vs. spread on the coupons, and different materials. For all conditions and viruses evaluated, the dose-response curves were nonlinear, such that the dose required to achieve a 1-log (or 90%) reduction could not be linearly extrapolated to predict a 3-log (or 99.9%) reduction. UVC light is more effective against SARS-CoV-2 on hard nonporous surfaces vs. on fabric, in an inoculum matrix of cell culture media vs. simulated saliva, and in wet droplets vs. dry droplets. The range of UVC doses measured by the Los Angeles County Metropolitan Transportation Authority during a field study with a specific pulsed xenon light configuration demonstrated that a 3-log reduction in SARS-CoV-2 would not be achievable for the majority of conditions evaluated in the laboratory experiments.