Far-UVC light: A new tool to control the spread of airborne-mediated microbial diseases

Abstract

Airborne-mediated microbial diseases such as influenza and tuberculosis represent major public health challenges. A direct approach to prevent airborne transmission is inactivation of airborne pathogens, and the airborne antimicrobial potential of UVC ultraviolet light has long been established; however, its widespread use in public settings is limited because conventional UVC light sources are both carcinogenic and cataractogenic. By contrast, we have previously shown that far-UVC light (207-222 nm) efficiently inactivates bacteria without harm to exposed mammalian skin. This is because, due to its strong absorbance in biological materials, far-UVC light cannot penetrate even the outer (non living) layers of human skin or eye; however, because bacteria and viruses are of micrometer or smaller dimensions, far-UVC can penetrate and inactivate them. We show for the first time that far-UVC efficiently inactivates airborne aerosolized viruses, with a very low dose of 2 mJ/cm² of 222-nm light inactivating >95% of aerosolized H1N1 influenza virus. Continuous very low dose-rate far-UVC light in indoor public locations is a promising, safe and inexpensive tool to reduce the spread of airborne-mediated microbial diseases.

Figure 1

Antiviral efficacy of different low doses of 222-nm far-UVC light. Typical fluorescent images of MDCK epithelial cells infected with influenza A virus (H1N1). The viruses were exposed in aerosolized form in the irradiation chamber to doses of 0, 0.8, 1.3 or 2.0 mJ/cm² of 222-nm far-UVC light. Infected cells fluoresce green (blue = nuclear stain DAPI; green = Alexa Fluor-488 conjugated to anti-influenza A antibody). Images were acquired with a 40× objective.

Figure 2

Quantification of the antiviral efficacy of 222-nm far-UVC light. Fractional survival, FFU_UV/FFU_controls, is plotted as a function of the 222-nm far-UVC dose. Means and standard deviations refer to triplicate repeat studies and the line represents the best-fit regression to Eqn 1 (see text).

Figure 3

Schematic diagram of the custom UV irradiation chamber. The chamber is depicted in a top down view. Components of the setup include: water bubbler for humidified air input (A), a desiccator for dry air input (B), a nebulizer (C), baffles (D), an RH and temperature meter (E), a particle sizer (F), far-UVC lamps (G), band pass filters (H), a far-UVC transmitting plastic window (I), a reflective aluminum surface (J), and a BioSampler (K). Pumps are used to pressurize the nebulizer for aerosol generation and to control flow through the system. Flow control valves allow adjustments through the system. HEPA filters are included on all air inputs and outputs. A set of three way valves controls flow to or around the BioSampler. The vertically stacked lamps are directed at the window in the side of the chamber to expose the aerosols passing horizontally. The additional films to uniformly decrease the dose were placed between the filters and the window. The path of the aerosolized virus within the system during sampling is indicated with the red dotted line.

Figure 4

Photograph of the custom UV irradiation chamber. The experimental setup shows many of the necessary components while some elements, such as pumps, filters, and lamps, were omitted to better depict the overall setup.