Leili Abkar, Karl Zimmermann, Fuhar Dixit, Ataollah Kheyrandish, Madjid Mohseni

COVID-19 pandemic lesson learned- critical parameters and research needs for UVC inactivation of viral aerosols

Journal of Hazardous Materials Advances,8 : 10083, 2022

The COVID-19 pandemic highlighted public awareness of airborne disease transmission in indoor settings and emphasized the need for reliable air disinfection technologies. This increased awareness will carry in the postpandemic era along with the ever-emerging SARS-CoV variants, necessitating effective and well-defined protocols, methods, and devices for air disinfection. Ultraviolet (UV)-based air disinfection demonstrated promising results in inactivating viral bioaerosols. However, the reported data diversity on the required UVC doses has hindered determining the best UVC practices and led to confusion among the public and regulators. This article reviews available information on critical parameters influencing the efficacy of a UVC air disinfection system and, consequently, the required dose including the system’s components as well as operational and environmental factors. There is a consensus in the literature that the interrelation of humidity and air temperature has a significant impact on the UVC susceptibility, which translate to changing the UVC efficacy of commercialized devices in indoor settings under varying conditions. Sampling and aerosolization techniques reported to have major influence on the result interpretation and it is recommended to use several sampling methods simultaneously to generate comparable and conclusive data. We also considered the safety concerns and the potential safe alternative of UVC, far-UVC. Finally, the gaps in each critical parameter and the future research needs of the field are represented. This paper is the first step to consolidating literature towards developing a standard validation protocol for UVC air disinfection devices which is determined as the one of the research needs. 1. Introduction Regional and global pandemics have imposed death tolls on society throughout the ages. The 2002 Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV) pandemic was followed in 2015 by the Middle East Respiratory Syndrome Coronavirus (MERS-CoV) outbreak. The emergence of the novel coronaviruses (SARS-CoV-2) caused the 2019 (COVID-19) pandemic. As of September 2022, over 6.49 million people have died from SARS-CoV-2 and its variants (World Health Organization WHO, 2022) and there have been significant socio-economic impacts (World Health Organization WHO, 2022). The global growth rate declined by 6.3% in 2020, a considerable drop (Statista Research Department, 2020). The original forecasted change in global GDP for 2020 was 2.9%, and due to the pandemic, the GDP declined by 3.4%, Abbreviations: CDC, centre for disease control and prevention (USA); CMD, count median diameter; DNA, deoxyribonucleic acid; DSB, double strand break; dsDNA, double-stranded deoxyribonucleic acid; Far-UVC, ultraviolet irradiation in the ‘far’ range of 200–230 nm; GTC, growth tube collectors; LED, light emitting diode; LPUV, low-pressure ultraviolet lamp; NIOSH, national institute for occupational safety and health; PBS, phosphate buffered saline; PRRS, porcine reproductive and respiratory syndrome; SARS-CoV-2, severe acute respiratory syndrome coronavirus-2; SSB, single strand break; ssRNA, single-stranded ribonucleic acid; REL, recommended exposure limit; RH, relative humidity; RNA, ribonucleic acid; ROS, reactive oxygen species; UV, ultraviolet irradiation; UVC, ultraviolet irradiation in the ‘C’, or germicidal, spectrum from 200 to 290 nm; UVGI, ultraviolet germicidal irradiation; UV-LED, light emitting diode in the ultraviolet range.  

Clysly Celine R. Ramos, Josemaria Lrenzo A. Roque,Diane B. Sarmiento, Luis Enrico G. Suarez, Janela Tanya P. Sunio, Kaezzy Ila B. Tabungar, Geraldine Susan C. Tengco, Phylis C. Rio, Allan L. Hilario

Use of ultraviolet-C in environmental sterilization in hospitals: A systematic review on efficacy and safety

International Journal of Health Sciences, 14, Issue 6 : 52-65, 2020  

Objectives: The study aimed to review the literature on the use of ultraviolet-C (UV-C) sterilization to assess its clinical efficacy in reducing risk and transmission of nosocomial infections as well as its associated health safety or hazards.

Methods: Four main search engines were used to identify potential studies which included: (1) Google Scholar, (2) ScienceDirect, (3) PubMed, and (4) Cochrane. Studies in English and published from 2010 to 2020 were considered. Studies on efficacy were limited to those in unseeded hospital environments, examining environmental disinfection, and with true experimental, randomized controlled trial, or quasiexperimental study designs. No additional criterion was used for safety studies due to the scarcity of literature. In the end, a total of 17 studies were selected. Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines were followed. Risk of bias assessment and manual data extraction and tabulation were done.

Results: Twelve eligible efficacy studies were identified together with five safety studies. It was found that UV-C irradiation had positive results when used as an adjunct for existing cleaning protocols. The germicidal effect of UV-C is potent against microorganisms including viruses, methicillin-resistant Staphylococcus aureus, and vancomycin-resistant enterococci. Safety study results showed dermal effects of UV-C exposure including DNA lesions, formation of cyclobutane pyrimidine dimers in cells, and effects on the skin’s stratum corneum.

Conclusion: It was found that UV-C can be utilized as an adjunct to terminal manual cleaning because of its efficacy as a germicidal agent. Further studies must still be done to exact a standard for safe exposure dose, especially for 222 nm germicidal lamps. Direct evidence is needed for any targeted implementation of UV-C during Coronavirus Disease 2019 (COVID-19) pandemic. 

Keywords: Ultraviolet-C, environmental sterilization, hospitals, systematic review, coronavirus disease-19 

Karyne Rangel, Fellipe O. Cabral, Guilherme C. Lechuga, Maria H. S. Villas-Bôa , Victor Midlej and Salvatore G. De-Simone 

Effectiveness Evaluation of a UV-C-Photoinactivator against Selected ESKAPE-E Pathogens 

International Journal of Environmental Research and Public Health, 19 : 16559, 2022  

Abstract: Healthcare-associated infections (HAI) worldwide includes infections by ESKAPE-E pathogens. Environmental surfaces and fomites are important components in HAI transmission dynamics, and shoe soles are vectors of HAI. Ultraviolet (UV) disinfection is an effective method to inactivate pathogenic microorganisms. In this study, we investigated whether the SANITECH UV-C shoe sole decontaminator equipment that provides germicidal UV-C radiation could effectively reduce this risk of different pathogens. Six standard strains and four clinical MDR strains in liquid and solid medium were exposed to a UV-C System at specific concentrations at other times. Bacterial inactivation (growth and cultivability) was investigated using colony counts and resazurin as metabolic indicators. SEM was performed to assess the membrane damage. Statistically significant reduction in cell viability for all ATCCs strains occurred after 10 s of exposure to the UV-C system, except for S. enterica, which only occurred at 20 s.
The cell viability of P. aeruginosa (90.9%), E. faecalis and A. baumannii (85.3%), S. enterica (82.9%), E. coli (79.2%) and S. aureus (71.9%) was reduced considerably at 20 s. In colony count, after 12 s of UV-C exposure, all ATCC strains showed a 100% reduction in CFU counts, except for A. baumannii, which reduced by 97.7%. A substantial reduction of colonies above 3 log10 was observed at 12 and 20 s in all bacterial strains tested, except for A. baumannii ATCC 19606 (12 s). The exposure of ATCCs bacterial strains to the UV-C system for only 2 s was able to reduce 100% in the colony forming units (CFU) count in all ATCCs strains, S. aureus, P. aeruginosa, E. coli, A. baumannii, E. faecalis, except the S. enterica strain which had a statistically significant reduction of 99.7%. In ATCC strains, there was a substantial decrease in colonies after 4 s (sec) of exposure to the UV-C system, with a reduction ranging from 3.78–4.15 log10 CFU/mL. This reduction was observed in MDR/ESKAPE-E strains within 10 s, showing that UV-C could eliminate above 3.84 log10 CFU/mL. SEM showed a reduction of pili-like appendages after UV-C treatment in all strains except for E. coli (ATCC 25922). The Sanitech UV-C shoe sole decontaminator equipment from Astech Serv. and Fabrication Ltd. (Petrópolis, Brazil), effectively killed in vitro a series of ATCCs and MDR/ESKAPE-E bacteria of sanitary interest, commonly found in the hospital environment. 

Keywords: UV-C; shoe sole decontaminator; ESKAPE-E pathogens; multidrug resistance; disinfection; cell viability; SEM

Sebastian Freeman, Karen Kibler, Zachary Lipsky, Sha Jin, Guy K.German & KaimingYe  

Systematic evaluating and modeling of SARS CoV 2 UVC disinfection

Scientific Reports, 12 : 5869, 2022 

The ongoing COVID-19 global pandemic has necessitated evaluating various disinfection technologies for reducing viral transmission in public settings. Ultraviolet (UV) radiation can inactivate pathogens and viruses but more insight is needed into the performance of diferent UV wavelengths and their applications. We observed greater than a 3-log reduction of SARS-CoV-2 infectivity with a dose of 12.5 mJ/cm2 of 254 nm UV light when the viruses were suspended in PBS, while a dose of 25 mJ/cm2 was necessary to achieve a similar reduction when they were in an EMEM culture medium containing 2%(v/v) FBS, highlighting the critical efect of media in which the virus is suspended, given that SARSCoV-2 is always aerosolized when airborne or deposited on a surface. It was found that SARS-CoV-2 susceptibility (a measure of the efectiveness of the UV light) in a bufer such as PBS was 4.4-fold greater than that in a cell culture medium. Furthermore, we discovered the attenuation of UVC disinfection by amino acids, vitamins, and niacinamide, highlighting the importance of determining UVC dosages under a condition close to aerosols that wrap the viruses. We developed a disinfection model to determine the efect of the environment on UVC efectiveness with three diferent wavelengths, 222 nm, 254 nm, and 265 nm. An inverse correlation between the liquid absorbance and the viral susceptibility was observed. We found that 222 nm light was most efective at reducing viral infectivity in low absorbing liquids such as PBS, whereas 265 nm light was most efective in high absorbing liquids such as cell culture medium. Viral susceptibility was further decreased in N95 masks with 222 nm light being the most efective. The safety of 222 nm was also studied. We detected changes to the mechanical properties of the stratum corneum of human skins when the 222 nm accumulative exposure exceeded 50 J/cm2 .The fndings highlight the need to evaluate each UV for a given application, as well as limiting the dose to the lowest dose necessary to avoid unnecessary exposure to the public.

Ana Rita Pereira, Daniel F.O. Braga, Mariana Vassal, Inês B. Gomes, Manuel Simões

Ultraviolet C irradiation: A promising approach for the disinfection of public spaces?   

Science of the total Environment, 879 : 163007, 2023

Ultraviolet irradiation C (UVC) has emerged as an effective strategy for microbial control in indoor public spaces. UVC is commonly applied for air, surface, and water disinfection. Unlike common 254 nm UVC, far-UVC at 222 nm is considered non-harmful to human health, being safe for occupied spaces, and still effective for disinfection purposes. Therefore, and allied to the urgency to mitigate the current pandemic of SARS-CoV-2, an increase in UVC-based technology devices appeared in the market with levels of pathogens reduction higher than 99.9 %. This environmentally friendly technology has the potential to overcome many of the limitations of traditional chemical-based disinfection approaches. The novel UVC-based devices were thought to be used in public indoor spaces such as hospitals, schools, and public transport to minimize the risk of pathogens contamination and propagation, saving costs by reducing manual cleaning and equipment maintenance provided by manpower. However, a lack of information about UVC-based parameters and protocols for disinfection, and controversies regarding health and environmental risks still exist. In this review, fundamentals on UVC disinfection are presented. Furthermore, a deep analysis of UVC-based technologies available in the market for the disinfection of public spaces is addressed, as well as their advantages and limitations. This comprehensive analysis provides valuable inputs and strategies for the development of effective, reliable, and safe UVC disinfection systems.