Toward a Test Protocol for Surface Decontamination Using a Mobile Whole-room UVGI Device^†

Mobile whole-room UVGI devices are used in healthcare settings to control surface-borne pathogens. Unfortunately, no standard method comparing the efficacy of these devices is available. We accessed the effect of shadows on UVC 254 nm inactivation. The evaluation of a mobile whole-room UVGI device used spores of Bacillus atrophaeus as a surrogate for Clostridium difficile and Staphylococcus aureus as a surrogate for MSRA. Inactivation after 10 min of exposure varied significantly depending on whether the spores received direct UV exposure (4.3 log reduction), both direct and reflected UV exposure (3.0-4.0 log reduction) or reflected UV exposure alone (<1.0 log reduction). The susceptibility (z-value) for inactivation of B. atrophaeus spores on a glass surface was estimated to be 0.00312 m²  J^-1 . Staphylococcus aureus microbial log reductions were approximately 5.5 for direct UV exposure, 3.6-5.2 for both direct and reflected UV exposure and approximately 2.75 for only reflected UV exposure. Our measurement of reflected dose ranged from 0.46% to 1.47%. Based on our findings, B. atrophaeus spores should be considered as a model organism for testing the impact of shadows on mobile whole-room UVGI device inactivation. Optimizing the reflected component of whole-room UVGI is important, especially for UVC-resistant organisms.