Impact of Room Location on UV-C Irradiance and UV-C Dosage and Antimicrobial Effect Delivered by a Mobile UV-C Light Device

OBJECTIVE. To evaluate ultraviolet C (UV-C) irradiance, UV-C dosage, and antimicrobial effect achieved by a mobile continuous UV-C device. DESIGN. Prospective observational study. METHODS. We used 6 UV light sensors to determine UV-C irradiance (W/cm(2)) and UV-C dosage (mu Wsec/cm(2)) at various distances from and orientations relative to the UV-C device during 5-minute and 15-minute cycles in an ICU room and a surgical ward room. In both rooms, stainless-steel disks inoculated with methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant Enterococcus (VRE), and Clostridium difficile spores were placed next to sensors, and UV-C dosages and log(10) reductions of target organisms achieved during 5-minute and 15-minute cycles were determined. Mean irradiance and dosage readings were compared using ANOVA. RESULTS. Mean UV-C irradiance was nearly 1.0E-03W/cm(2) in direct sight at a distance of 1.3m (4 ft) from the device but was 1.12E-05W/cm(2) on a horizontal surface in a shaded area 3.3m (10 ft) from the device (P<.001). Mean UV-C dosages received by UV-C sensors located at different distances and orientation relative to the device varied significantly during 5-minute cycles and during 15-minute cycles (P<. 001). Log(10) reductions ranged from > 4 to 1-3 for MRSA, > 4 to 1-2 for VRE and > 4 to 0 log(10) for C. difficile spores, depending on the distance from, and orientation relative to, the device with 5-minute and 15-minute cycles. CONCLUSION. UV-C irradiance, dosage, and antimicrobial effect received from a mobile UV-C device varied substantially based on location in a room relative to the UV-C device.