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

Area of Science:

• Microbiology
• Infectious Disease Control
• Environmental Science

Background:

• Mobile whole-room UV germicidal irradiation (UVGI) devices are crucial for controlling surface pathogens in healthcare.
• A lack of standardized methods hinders the comparison of UVGI device efficacy.
• Understanding the impact of shadows on UVGI inactivation is essential for optimizing disinfection protocols.

Purpose of the Study:

• To evaluate the effect of shadows on the inactivation efficacy of a mobile whole-room UVGI device.
• To compare the performance of UVGI against direct, reflected, and combined UV exposure using microbial surrogates.
• To establish a model organism for assessing UVGI performance under shadowed conditions.

Main Methods:

• Utilized Bacillus atrophaeus spores as a surrogate for Clostridium difficile and Staphylococcus aureus for Methicillin-resistant Staphylococcus aureus (MRSA).
• Exposed microbial surrogates to UVC 254 nm light from a mobile whole-room UVGI device for 10 minutes.
• Measured log reductions in microbial populations under conditions of direct UV, reflected UV, and combined exposure; quantified reflected UV dose.

Main Results:

• Inactivation varied significantly based on UV exposure type: direct UV yielded 4.3 log reduction (B. atrophaeus) and 5.5 log reduction (S. aureus).
• Reflected UV exposure alone resulted in <1.0 log reduction (B. atrophaeus) and ~2.75 log reduction (S. aureus).
• Combined direct and reflected UV exposure showed intermediate log reductions, with reflected dose measuring 0.46%–1.47%.

Conclusions:

• Bacillus atrophaeus spores are a suitable model organism for testing the impact of shadows on mobile whole-room UVGI device efficacy.
• Optimizing the reflected component of UVGI is critical, particularly for inactivating UVC-resistant microorganisms.
• Standardized methods are needed to compare mobile whole-room UVGI devices, considering shadow effects for effective pathogen control.