Candida auris is an emerging fungal superbug of worldwide interest. It is associated with high mortality rates and exhibits increased resistance to antifungals. Ultraviolet subtype C (UVC) light can be used to disinfect surfaces to mitigate its spread. The objectives of this study were (1) To investigate UVC disinfection performances and wavelength sensitivity of C. auris . (2) To evaluate the UVC dose required for the prevention of biofilm formation on stainless‐steel, plastic (polystyrene), and poly‐cotton fabric surfaces. C. auris was grown following standard procedures. The study utilized six different UVC LED arrays with wavelengths between 252 and 280 nm. Arrays were set at similar intensities, to obtain doses of 5–40 mJ cm −2 and similar irradiation time. Disinfection performance for each array was determined using log reduction value (LRV) and percentage reduction by comparing the controls against the irradiated treatments. Evaluation of the ability of 267 nm UVC LEDs to prevent C. auris biofilm formation was investigated using stainless‐steel, plastic coupons, and poly‐cotton fabric. Peak sensitivity to UVC disinfection was between 267 and 270 nm. With 20 mJ cm −2 , the study obtained ≥LRV3. On stainless‐steel coupons, 30 mJ cm −2 was sufficient to prevent biofilm formation, while on plastic, this required 10 mJ cm −2 . A dose of 60 mJ cm −2 reduced biofilms on poly‐cotton fabric significantly ( R 2 = 0.9750, p = 0.0002). The study may allow for the design and implementation of disinfection systems.

Vehicle Heating, ventilation, and air conditioning (HVAC) systems can accumulate and recirculate highly infectious respiratory diseases via aerosols. Integrating Ultraviolet Subtype C (UVC) light-emitting diodes (LEDs) to complement automobile HVAC systems can protect occupants from developing allergies, experiencing inflammatory problems, or acquiring respiratory infectious diseases by inactivating pathogenic organisms. UVC can add little to no static pressure with minimal space, unlike mercury lamps which are larger and heavier. Additionally, UVC LEDs are effective at low voltage and have no mercury or glass. While previous experiments have shown UVC LED technology can reduce bacteriophage Phi6 concentrations by 1 log in 5 min (selected as the average time to clean the cabin air), those studies had not positioned LED within the HVAC itself or studied the susceptibility of the surrogate at the specific wavelength. This study aimed to assess the disinfection performance of UVC LEDs in automotive HVAC systems and determine the dose–response curve for bacteriophage Phi6, a SARS-CoV-2 surrogate. To achieve this, UVC LEDs were installed in a car HVAC system. To determine inactivation efficacy, a model chamber of 3.5 m3, replicating the typical volume of a car, containing the modified automobile HVAC system was filled with bacteriophage Phi6, and the HVAC was turned on with and without the UVC LEDs being turned on. The results revealed that HVAC complemented with UVC reduced bacteriophage Phi6 levels significantly more than the HVAC alone and reduced the viral concentration in the cabin by more than 90% viral reduction in less than 5 min. The performance after 5 min is expected to be significantly better against SARS-CoV-2 because of its higher sensitivity to UVC, especially at lower wavelengths (below 270 nm). HVAC alone could not achieve a 90% viral reduction of bacteriophage Phi6 in 15 min. Applying UVC LEDs inside an HVAC system is an effective means of quickly reducing the number of aerosolized viral particles in the chamber, by inactivating microorganisms leading to improved cabin air quality.

Mold growth in HVAC systems poses a threat to human health, increases facility management operating costs due to decreased air flow efficiency, and damages buildings, impacting buildings' attractiveness in an ever more competitive property market concerned with both carbon footprint and ventilation quality. Although UVC treatment of HVAC systems has been shown to reduce growth, efficient design requires a specified amount of UVC dose coupled with a specific dosing strategy. UVC disinfection efficacy and wavelength sensitivity of spores from the most common and notorious black mold, Cladosporium halotolerans is not known. This study investigates the sensitivity of C. halotolerans and demonstrates that growth of black mold on HVAC coils can be effectively prevented with a periodic dosing scheme using commercially available UVC LEDs. Multiple UVC LED arrays with varying wavelength peaks in the range of 252-280 nm were used to demonstrate the spectral sensitivity of C. halotolerans by keeping the wavelength specific UVC dose equal in order to avoid bias. The data obtained for doses of 25, 75, 125, 175, and 225 mJ/cm2 was used. The data obtained was used to determine a dose response curve and susceptibility patterns. Disinfection performances for the arrays were determined using log reduction value (LRV) by comparing the controls against the irradiated treatments. To study mold growth prevention on HVAC coils, the 267 nm array which had the best disinfection efficacy was utilized. The coils were placed in a chamber with a temperature set at 24 °C and relative humidity (RH) at 96%. Unlike the controls, the test coil was irradiated with a dose of 28.8 mJ/cm2 every 12 hours. The coils were monitored, and observations were recorded using time-lapse videos. The highest disinfection level of black mold observed in the range of 250-280nm occurred at 267 nm, with 225 mJ/cm2 obtaining 4.03 LRV. Linear regression analysis at 95% for 252 nm (R2=0.9637, p=0.0030), 261 nm (R2=0.9711, p=0.0021), 267 nm (R2=0.9723, p=0.0020), 270 nm (R2=0.9819, p=0.0010), 273 nm (R2=0.9878, p=0.0006), and 280 nm (R2=0.9914, p=0.0003) displayed significant association between arrays' peak wavelengths and disinfection performances against C. halotolerans. The study revealed that a higher dose of 225 mJ/cm2 is required to disinfect C. halotolerans by 99.99% (4.03 LRV). However, using a periodic dosing strategy utilizing 28.8 mJ/cm2 prevented any mold growth, while the fungal levels in the positive control increased. The study allows for the design and implementation of mold growth prevention strategies in HVAC systems to improve health and lower operating costs.

Background: Candida auris is an emerging fungal pathogen of worldwide interest. It is associated with high mortality rates and exhibits increased resistance to antifungals. Ultraviolet-C (UVC) light can be used to disinfect surfaces to mitigate its spread. In this study, we analyzed the performance of different UVC wavelengths against C. auris to determine its wavelength sensitivity and UVC dose requirements and evaluated biofilm prevention dose requirements on most used materials in healthcare settings. Objectives: 1. To investigate UVC disinfection performances and wavelength sensitivity of C. auris; 2. To evaluate the UVC dose required for prevention of biofilm prevention on stainless steel. Methods: C. auris was grown following standard procedures. The study utilized six different UVC LED arrays with wavelengths between 252 and 280 nm. Arrays were set at similar intensities, to obtain doses of 5-40 mJcm-2 and similar irradiation time. Disinfection performance for each array was determined using log reduction value (LRV) and percentage reduction by comparing the controls against the irradiated treatments. Evaluation of the ability of 267 nm UVC LEDs to prevent C. auris biofilm formation was investigated using stainless steel, plastic coupons, and poly-cotton fabric. Results: Peak sensitivity to UVC disinfection was between 267 and 270 nm. With 20 mJcm-2, the study obtained LRV 3. On steel coupons, 30 mJcm-2 was sufficient to prevent biofilm formation, on plastic only 10 mJcm-2. A dose of 60 mJcm-2 reduced biofilms on poly-cotton fabric significantly. Conclusions: Results revealed that C. auris was most susceptible at 267-270 nm. Additional highlights from the study allow for the design and implementation of disinfection systems.

Vehicle HVAC systems can accumulate and recirculate highly infectious respiratory diseases via aerosols. Integrating UVC to complement automobile HVAC systems can protect occupants from developing allergies, experiencing inflammatory problems, or acquiring respiratory infectious diseases by inactivating pathogenic organisms. UVC can add little to no static pressure with minimal space, unlike mercury lamps which are larger and heavier. Additionally, UVC LEDs are effective at low voltage and have no mercury or glass. While previous experiments have shown UVC LED technology can reduce bacteriophage Phi6 concentrations by 1 log in 5 minutes (selected as the average time to clean the cabin air), those studies had not positioned LED within the HVAC itself or studied the susceptibility of the surrogate at the specific wavelength. This study aimed to assess the disinfection performance of UVC LEDs in automotive HVAC systems and determine the dose-response curve for bacteriophage Phi6, a SARS-CoV-2 surrogate. To achieve this, UVC LEDs were installed in a car HVAC system. To determine inactivation efficacy, a model chamber of 3.5 m3, replicating the typical volume of a car, containing the modified automobile HVAC system was filled with bacteriophage Phi6, and the HVAC was turned on with and without the UVC LEDs being turned on. The results revealed that HVAC complemented with UVC reduced bacteriophage Phi6 levels significantly more than the HVAC alone and reduced the viral concentration in the cabin by more than 1 LRV (90% viral reduction) in less than 5 minutes. The performance after 5 minutes is expected to be significantly better against SARS-CoV-2 because of its higher sensitivity to UVC, especially at lower wavelengths (below 270 nm). HVAC alone could not achieve a 90% viral reduction of bacteriophage Phi6 in 15 minutes. Applying UVC LEDs inside an HVAC system is an effective means of quickly reducing the number of aerosolized viral particles in the chamber, by inactivating microorganisms leading to improved cabin air quality.