Abstract
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/cm2) and UV-C dosage (µWsec/cm2) 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 log10 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-03 W/cm2 in direct sight at a distance of 1.3 m (4 ft) from the device but was 1.12E-05 W/cm2 on a horizontal surface in a shaded area 3.3 m (10 ft) from the device (P4 to 1-3 for MRSA, >4 to 1-2 for VRE and >4 to 0 log10 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. Infect Control Hosp Epidemiol 2016;37:667-672.
Highlights
We evaluated ultraviolet light (UV)-C irradiance and dosages achieved when sensors were oriented at 0° angles relative to the device to mimic dosage received by horizontal surfaces in hospital rooms
Clinical strains of methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus (VRE), and Clostridium difficile strain ATCC 9689 were used as target organisms
Results obtained with qualitative photochromic dosage indicator labels and dosages measured using radiometric ultraviolet C (UV-C) light sensors placed at various distances from and orientations relative to the UV device after a 15-minute cycle
Summary
Clinical strains of methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus (VRE), and Clostridium difficile strain ATCC 9689 were used as target organisms. MRSA and VRE isolates were inoculated onto blood agar plates and incubated overnight at 37°C. For these 2 organisms, colonies from blood agar were used to make separate suspensions equivalent to a 0.5 McFarland standard in normal saline for inoculation onto disks. C. difficile spores were produced by inoculating the organism onto 10 horse-blood-agar plates (Remel, Lenexa, KS), which were incubated anaerobically for 5–7 days at 37°C. After 7 days, spores were transferred to a tube containing 10 mL sterile dH2O and absolute alcohol (50/50 concentration) and stored at 4°C for further use For both MRSA and VRE, 10 μL suspensions were inoculated over the entire surface of sterilized stainless-steel disks (1 cm diameter; Muzeen and Blythe, Winnepeg, Canada) and allowed to dry at room temperature in a BSC. Colony counts were determined after incubation for 48 hours for MRSA and VRE and 96 hours for C. difficile
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