Ultraviolet-C (UV-C) monitoring made simple: Colorimetric indicators to assess delivery of UV-C light by room decontamination devices.

OBJECTIVE: To evaluate the use of colorimetric indicators for monitoring ultraviolet-C (UV-C) light delivery to sites in patient rooms. METHODS: In laboratory testing, we examined the correlation between changes in color of 2 commercial colorimetric indicators and log10 reductions in methicillin-resistant Staphylococcus aureus (MRSA) and Clostridioides difficile spores with exposure to increasing doses of UV-C from a low-pressure mercury room decontamination device. In patient rooms, 1 of the colorimetric indicators was used to assess UV-C dose delivery to 27 sites in the room. RESULTS: In laboratory testing, the manufacturer's reference colors for MRSA and C. difficile reduction corresponded with doses of ∼10,000 and 46,000 µJ/cm2; these doses resulted in >3 log10 reductions in MRSA and C. difficile spores, respectively. In patient rooms, the colorimetric indicators demonstrated suboptimal delivery of UV-C dosing to shadowed areas, which was improved by providing cycles on each side of the patient bed rather than in a single position and altering device placement. Increasing duration of exposure increased the number of sites achieving adequate dosing to kill C. difficile spores. CONCLUSIONS: Commercial colorimetric indicators provide rapid and easy-to-interpret information on the UV-C dose delivered to sites in patient rooms. The indicators may be useful for training environmental services personnel and optimizing the effectiveness of UV-C room decontamination devices.

Inactivation of Pathogens in Air Using Ultraviolet Direct Irradiation Below Exposure Limits.

A method is described for inactivation of pathogens, especially airborne pathogens, using ultraviolet (UV) radiation emitted directly into occupied spaces and exposing occupants to a dose below the accepted actinic exposure limit (EL). This method is referred to as direct irradiation below exposure limits, or DIBEL. It is demonstrated herein that low-intensity UV radiation below exposure limits can achieve high levels of equivalent air changes per hour (ACHeq) and can be an effective component of efforts to combat airborne pathogens such as the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus that causes coronavirus disease 2019 (COVID-19). An ACHeq of 4 h-¹ is presently achievable over a continuous 8 h period for the SARS-CoV-2 virus with UV-C light-emitting diodes (LEDs) having peak wavelength at 275 nm, and future improvements in LED technology and optics are anticipated to enable improvements up to 150 h-¹ in the coming decade. For example, the actinic EL is 60 J/m² at 254 nm, and human coronaviruses, including SARS-CoV-2, have a UV dose required for 90 % inactivation of about 5 J/m² at 254 nm. Irradiation by 254 nm UV-C at the EL is expected to provide 90 % inactivation of these organisms in air in about 40 min when the UV-C is delivered at a constant irradiance over 8 h, or in about 5 min if the UV-C is delivered at a constant irradiance over 1 h. Since the irradiation is continuous, the inactivation of initial contaminants accumulates to 99 % and then 99.9 %, and it also immediately begins inactivating any newly introduced (e.g., exhaled) pathogens at the same rate throughout the 8 h period. The efficacy for inactivating airborne pathogens with DIBEL may be expressed in terms of ACHeq, which may be compared with conventional ventilation-based methods for air disinfection. DIBEL may be applied in addition to other disinfection methods, such as upper room UV germicidal irradiation, and mechanical ventilation and filtration. The ACHeq of the separate methods is additive, providing enhanced cumulative disinfection rates. Conventional air disinfection technologies have typical ACHeq values of about 1 h-¹ to 5 h-¹ and maximum practical values of about 20 h-¹. UV-C DIBEL currently provides ACHeq values that are typically about 1 h-¹ to 10 h-¹, thus either complementing, or potentially substituting for, conventional technologies. UV-C DIBEL protocols are forecast herein to evolve to >100 ACHeq in a few years, potentially surpassing conventional technologies. UV-A (315 nm to 400 nm) and/or UV-C (100 nm to 280 nm) DIBEL is also efficacious at inactivating pathogens on surfaces. The relatively simple installation, low acquisition and operating costs, and unobtrusive aesthetic of DIBEL using UV LEDs contribute value in a layered, multi-agent disinfection strategy.

Efficacy of an ultraviolet-A lighting system for continuous decontamination of health care-associated pathogens on surfaces.

We found that ultraviolet-A (UV-A) light exposure resulted in a modest reduction in recovery of methicillin-resistant Staphylococcus aureus (MRSA), Candida auris, bacteriophage MS2, and bacteriophage Phi X174, but not Clostridioides difficile spores, on steel disk carriers. Four hours of UV-A exposure from a ceiling light fixture resulted in a significant reduction in pathogenic microorganisms recovered from in-use medical equipment. These findings suggest that UV-A could be useful as a means to provide continuous low-level decontamination of surfaces in health care facilities.

A comparison of the efficacy of multiple ultraviolet light room decontamination devices in a radiology procedure room.

OBJECTIVE: To evaluate the efficacy of multiple ultraviolet (UV) light decontamination devices in a radiology procedure room. DESIGN: Laboratory evaluation. METHODS: We compared the efficacy of 8 UV decontamination devices with a 4-minute UV exposure time in reducing recovery of methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant Enterococcus (VRE), and Clostridium difficile spores on steel disk carriers placed at 5 sites on a computed tomography patient table. Analysis of variance was used to compare reductions for the different devices. A spectrometer was used to obtain irradiance measurements for the devices. RESULTS: Four standard vertical tower low-pressure mercury devices achieved 2 log10CFU or greater reductions in VRE and MRSA and ~1 log10CFU reductions in C. difficile spores, whereas a pulsed-xenon device resulted in less reduction in the pathogens (P<.001). In comparison to the vertical tower low-pressure mercury devices, equal or greater reductions in the pathogens were achieved by 3 nonstandard low-pressure mercury devices that included either adjustable bulbs that could be oriented directly over the exam table, a robotic base allowing movement along the side of the table during operation, or 3 vertical towers operated simultaneously. The low-pressure mercury devices produced primarily UV-C light, whereas the pulsed-xenon device produced primarily UV-A and UV-B light. The time required to move the devices from the corner of the room and set up for operation varied from 18 to 59 seconds. CONCLUSIONS: Many currently available UV devices could provide an effective and efficient adjunct to manual cleaning and disinfection in radiology procedure rooms.