Field trial assessing the antimicrobial decontamination efficacy of gaseous ozone in a public bus setting

Abstract

The widespread COVID-19 pandemic caused by the Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) necessitated measures aimed at preventing the spread of SARS-CoV-2. To mitigate the risk of fomite-mediated transmission, environmental cleaning and disinfection regimes have been widely implemented. However, conventional cleaning approaches such as surface wipe downs can be laborious and more efficient and effective disinfecting technologies are needed. Gaseous ozone disinfection is one technology which has been shown to be effective in laboratory studies. Here, we evaluated its efficacy and feasibility in a public bus setting, using murine hepatitis virus (a related betacoronavirus surrogate) and the bacteria Staphylococcus aureus as test organisms. An optimal gaseous ozone regime resulted in a 3.65-log reduction of murine hepatitis virus and a 4.73-log reduction of S. aureus, and decontamination efficacy correlated with exposure duration and relative humidity in the application space. These findings demonstrated gaseous ozone disinfection in field settings which can be suitably translated to public and private fleets that share analogous characteristics.

Keywords: Antimicrobial efficacy; Field trial; Gaseous ozone; Murine coronavirus; Staphylococcus aureus.

Graphical abstract

Fig. 1

Experimental set-up in a double decker bus in Phase 1. A) Sixteen carriers were spiked with MHV or S. aureus, 8 carriers in the top deck and 8 carriers in the bottom deck. Along with positions of the gaseous ozone generators and fans for circulation. The same set-up was performed in the control bus, but without the generator and fans. B) Schematic diagram showing the positioning of the contaminated carriers, with the contaminated side facing either the wall, floor, or ceiling.

Fig. 2

Experimental set-up in a single deck bus in Phase 2. A) Sixteen carriers were spiked with MHV (8 carriers) or S. aureus (8 carriers). Along with positions of the gaseous ozone generator and humidifiers. The same set-up was done in the control bus, but only without the ozone generator. B) Schematic showing the positioning of the contaminated carriers, with the contaminated side facing either the wall, floor, or ceiling. C) Photograph of the humidifiers set-up in both control and test buses.

Fig. 3

Phase 1 efficacy test. Measurements of ozone concentration in the A) MHV decontamination cycle, and the B) S. aureus decontamination cycle. Recovery of C) MHV and D) S. aureus from control and ozone exposed carriers, and their respective log reduction (Median (Solid line) with upper and lower quartiles (dotted lines), t-test **** p < 0.0001).

Fig. 4

Phase 2 efficacy test results with increased humidity. Measurements of A) ozone concentration and B) humidity during the decontamination cycle. Recovery of C) MHV and D) S. aureus from control and ozone exposed carriers, and their respective log reduction (Median (Solid line) with upper and lower quartiles (dotted lines), t-test **** p < 0.0001).

Fig. 5

Phase 2 efficacy test with increased incubation time. Measurements of A) ozone concentration during the decontamination cycle. Recovery of B) MHV and C) S. aureus from control and ozone exposed carriers, and their respective log reduction (Median (Solid line) with upper and lower quartiles (dotted lines), t-test **** p < 0.0001).