Indicazioni ad interim per l’uso dell’irradiazione UV germicida nel contesto della pandemia COVID-19

Abstract

The ultraviolet radiation in the range 100 -280 nm (UV-C) has a well-known germicidal efficiency due to the disruptive mechanism on the nucleic acids, RNA and DNA, of microorganisms. The UV-C based disinfecting technology is commonly used, for example, in biosafety cabinets in hospitals and laboratories. Although the UV-C would be useful for its germicidal action, caution must be used when the UV-C use could imply human exposure. The phototoxicity of the UV-C radiation can induce damage to most external organs, eyes and skin and exposure limits for acute effects must be respected in order to protect the human health and safety. In addition, the UV-C radiation is known to have stochastic effects and for this reason has been classified by the IARC (International Agency for Research on Cancer) as a class I carcinogenic agent. The COVID-19 pandemic outbreak raised the question of disinfecting living and working environments especially when they are shared by many people, this issue being particularly urgent in hospitals where the viral concentration due to patients affected by Covid-19 can be very high. Although the hospitals are the environments that most need disinfection, also transport means, markets, schools, commercial centers have to be disinfected in order to control the spreading of the infection. The effectiveness of the UV-C against microorganisms aroused a great interest during the pandemic outbreak, and several new devices for disinfection based on this technology have been proposed in the market with different use. Although there is lack of studies determining precisely the lethal UV-C dose in the case of COVID-19, many studies have been carried out in the recent past regarding the UV-C inactivation efficiency against very similar microorganisms, such as those causing the SARS and the MERS belonging to the same family Coronaviridae. The effectiveness of UV-C radiation in killing microorganisms, including respiratory viruses that were found relatively highly susceptible, is well assessed, but caution must be used when the use of UV-C based technology implies human exposure. The right compromise between effective disinfection objective and human health protection must be found, quantitatively evaluating each specific situation. The limit of human exposure must be respected and an accurate cost/benefit ratio must be evaluated in the case of doses well below the exposure limits for acute effects. In this work, the concepts of lethal dose in terms of irradiance and exposure time are discussed in the light of the human exposure limits with respect to different UV-C radiation practical applications.Examples are drawn by the literature and by the direct experience of the authors.This work is addressed, in particular, to health physicists and biomedical engineers. Technical personnel with adequate expertise could use these indications for developing and maybe sharing specific experiences. Further research is recommended at the aim of improving the disinfection techniques based on optical radiation. Beyond the epidemic conjuncture, this work could be useful also in fighting the increasing spread of multiresistant bacteria in hospitals reducing healthcare personnel exposure to complex mixtures of disinfectants