Multiple ILT1000 Systems Used in UV-C Effectiveness Study

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

Journal: Infection Control & Hospital Epidemiology

Authors: John M. Boyce, MD; Patricia A. Farrel, MT; Dana Towle, EdD; Renee Fekieta, PhD; Michael Aniskiewicz, MT

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 1.3m (4 ft) from the device but was 1.12E-05 W/cm2 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). Log10 reductions ranged from >4 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.


Excerpted from "Methods" Section:

UV-C Light Measurements

UV-C light measurements were obtained using model ILT254 (ILT1254) radiometric UV-C light sensors (International Light Technologies, Peabody, MA) equipped with calibrated National Institute of Standards and Technology (NIST)-traceable UV-C detectors with 254-nm filters and wide-angle diffusers. UV-C irradiance (W/cm2) readings were recorded using Data Logger software provided by the manufacturer. UV-C dosage (Wsec/cm2) was determined at each sensor by adding all irradiance readings obtained every second during a cycle. UV-C dosage readings were subsequently converted to μWsec/cm2. UV-C irradiance and dosage were measured using several protocols. To assess the variability of UV-C readings obtained with the light sensors placed at different distances and in various orientations relative to the UV-C device, triplicate readings were obtained with sensors in fixed positions (ie, readings were taken during 3 cycles without moving sensors) and 25 minutes between cycles.

We conducted 5-minute and 15-minute fixed-position cycles in an intensive care unit (ICU) room 29.16m2 (324 sq ft) in size and in a room 27m2 (300 sq ft) in size on a standard surgical ward. Rooms have standard wall paint, Marmoleum floors, dropped ceiling tiles, standard hospital beds, and in the ICU, physiologic monitoring devices. Temperature and humidity readings were not obtained. Rooms are maintained at temperatures between 68° and 75°F and at relative humidity of 30%–60%. The ICU room has 12 air changes per hour (ACH), and the surgical ward room has 6 ACH.

We placed 6 UV-C sensors simultaneously in different locations in a patient room. To promote standardized methods for evaluating the performance of mobile UV-C devices, we placed sensors at distances (1.2m [4 ft] and 3.3m [10 ft]) utilized by other investigators. We also evaluated 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. First, 2 sensors were oriented vertically and pointed directly at the UV-C device at distances of 1.3m and 3.3m from the device, then 2 sensors were oriented at a 0° angle to light emitted from the device (sensors lying flat on surfaces and pointed at ceiling) at distances of 1.3m and 3.3m. Finally, 2 sensors were oriented at a 0° angle to the light source and in shaded sites (indirect light) at distances of 1.3m and 3.3 m. For each of the latter 2 experimental conditions, an opaque object oriented vertically was placed immediately next to the sensor and between the sensor and light coming directly from the UV-C device. No sensors were placed at a 90° angle opposite the UV-C device.

In addition, during a 15-minute cycle, qualitative photochromic UV-C indicator labels provided by the device manufacturer were placed on the radiometric UV-C sensors to assess color changes at varying dosages. The labels, which are initially white, develop increasingly darker shades of pink as the dosage received increases.


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