222 nm far-UVC light markedly reduces the level of infectious airborne virus in an occupied room

Abstract

An emerging intervention for control of airborne-mediated pandemics and epidemics is whole-room far-UVC (200-235 nm). Laboratory studies have shown that 222-nm light inactivates airborne pathogens, potentially without harm to exposed occupants. While encouraging results have been reported in benchtop studies and in room-sized bioaerosol chambers, there is a need for quantitative studies of airborne pathogen reduction in occupied rooms. We quantified far-UVC mediated reduction of aerosolized murine norovirus (MNV) in an occupied mouse-cage cleaning room within an animal-care facility. Benchtop studies suggest that MNV is a conservative surrogate for airborne viruses such as influenza and coronavirus. Using four 222-nm fixtures installed in the ceiling, and staying well within current recommended regulatory limits, far-UVC reduced airborne infectious MNV by 99.8% (95% CI: 98.2-99.9%). Similar to previous room-sized bioaerosol chamber studies on far-UVC efficacy, these results suggest that aerosolized virus susceptibility is significantly higher in room-scale tests than in bench-scale laboratory studies. That said, as opposed to controlled laboratory studies, uncertainties in this study related to airflow patterns, virus residence time, and dose to the collected virus introduce uncertainty into the inactivation estimates. This study is the first to directly demonstrate far-UVC anti-microbial efficacy against airborne pathogens in an occupied indoor location.

Figure 1

Laboratory study results on inactivation of different aerosolized viruses exposed to graded doses of 222 nm far-UVC in a benchtop aerosol chamber. Results for aerosolized MNV are compared with human influenza A H1N1virus and human OC43 coronavirus. Fractional survival TCID_50,UVC/TCID_{50, controls} are plotted as a function of the 222-nm far-UVC dose. Values are reported as mean ± SD (n = 3) and the curves represents the best-fit robust bi-exponential regression (Eq. 1).

Figure 2

Measured reduction of pseudo steady-state murine norovirus (MNV) load in air samples collected in a mouse-cage changing room during routine work activities of the animal husbandry staff. Normalized MNV surviving fraction are shown on a log scale with far-UVC (n = 12 measurements) or without far-UVC (n = 8 measurements) ± SD.

Figure 3

The mouse-cage changing room. (a) Floorplan of the mouse-cage changing room with the measured interpolated horizontal irradiance data overlaid. Horizontal irradiance was measured at 1.8 m. The locations of the four lamps on the ceiling are indicated with filled black circles. The position of the air sampler (used at 2.1 m) is marked with a star. (b) Photo of a section of the room showing the four far-UVC lamps turned on and the location of the shelf where the MD8 portable air sampler was located during air sampling.