Healthcare infections are infections that patients and healthcare workers contract while in a health care setting. They can be caused by a range of microorganisms including bacteria, fungi and viruses present in the hospital environment and can result in serious illness including, since the beginning of 2020, COVID-19. Decontamination of environmental surfaces is critical in reducing and preventing the transmission of pathogens. Thus, in healthcare facilities appropriate cleaning and disinfection protocols need to be carefully selected with particular attention given to surfaces with a high probability of contagion. Given the limitations of manual disinfection methods, it is extremely important to introduce optimized automated non-touch disinfection methods, such as hydrogen peroxide vapor and UV-C irradiation. Automated non-touch methods avoid human error during the disinfection procedure, allows for frequently repeat disinfection cycles on high-touch surfaces (for example the CT bed and the chair needed to conduct nasopharyngeal swabs that need to be disinfected between one patient and the next), and to limit the risk of contaminating cleaning staff who perform manual disinfection after the automated cleaning has taken place.
In the ultraviolet spectrum, UV-C has the highest disinfection capacity with an efficacy peak at 265nm . Presently, the radiation wavelength most used is that supplied by low pressure mercury lamps (254nm), which have the advantage of being cheap and easily available. The main drawback on their use is that there are strict environmental protocols on the disposal of mercury . The 270-280nm radiation produced by LED is as effective as the 254nm radiation . LED technology has the advantage that lamps can be produced with very small dimensions and customizable geometries and they don’t contain harmful metals, although their main disadvantage is that they are very expensive to fabricate. Recently, the use of the 222nm radiation lamp has been promulgated with the idea that this shorter wavelength radiation might be less harmful to those exposed . However, these lamps are still very expensive and very bulky, and they still require careful supervision to avoid damage to the skin and to the eyes. Numerous studies are underway to establish the disinfection power of the UV-B (280-320nm) and UV-A (320-400nm) bands. At the time of writing, there were very few published results  that indicate the effectiveness of these spectral bands to disinfect SARS-CoV-2 contaminated surfaces.
To date, only mercury lamps can therefore be used to disinfect surfaces in hospital environments. There are numerous mercury lamps available on the market, varying in power, geometry and the shape of the reflectors. To achieve the necessary disinfection, however, it is essential to choose the correct lamps for the environment they are going to be used in, and above all to position them in an optimal way, something that requires both suitable equipment and the adequate training of staff to be able to use this equipment; these conditions are often not present in healthcare facilities.
The intention of our study, therefore, was to present practical and simple advice for UV-C disinfection which includes guidance as to the choice and positioning of the lamps, a method to reduce the error on the calculation of the exposure time and provide a way to check irradiation by using proper UV-C dosimeters. The choice of the lamp depends on the type of environment or surface to be disinfected; in the case of smaller rooms or elongated surfaces (such as beds), low power lamps (32 or 36 W) with long tubes (120 or 150 cm) are to be preferred. In the case of large rooms, it is necessary to use more powerful (and thus more expensive) lamps (36x2 W or 55x2 W). In both cases, the presence of side and rear reflectors made of highly reflective material allows to significantly increase the spatial uniformity of the irradiance and to recover the radiation delivered in non-useful direction.
The positioning of the lamps also depends on the type of environment or surface to be disinfected: lamps on mobile supports seem generally better at disinfecting surfaces, whereas lamps fixed on ceilings or walls are preferable when whole rooms need to be disinfected. In choosing the number of lamps to be installed, attention must be paid to surfaces at angles greater than 45° with respect to the irradiation source; in this case, especially in the absence of side and rear reflectors, it is advisable to increase the number of lamps used. It is also important to remember that only surfaces that are exposed to the direct light from the lamp will be irradiated; the reflected component of the primary radiation from common materials contributes minimally to sterilization. This is certainly the main limitation of the UVC disinfection method which must therefore be proposed in addition to and not as a substitute for standard decontamination procedures.
It is the calculation of the exposure time for successful disinfection that poses the greatest challenge to establishing a disinfection protocol. The most recent studies on the subject provide the dose value necessary to obtain the inactivation of SARS-CoV-2. However, if the virus is present in dry biofilms deposited on surfaces, then the resistance to sterilization could be greater. Pending more studies on this subject, it is prudent to multiply the dose obtained in the laboratory by a factor of 10 in real-life environments. Once the disinfection dose is known, the irradiation time can be calculated by dividing this value by the irradiance of the lamp, obtained by applying the inverse square law to the irradiance value at 1m supplied by the manufacturer. In the absence of direct measurements of the irradiance, there are numerous reasons for error that can affect the irradiation time calculated, the most significant of which seem to be the position of the object at angles greater than 45° with respect to the irradiation source (in the absence of proper side reflectors) and not compensating for the time required for the emission to be fully operational. In the case of lamps whose shape is very different from that of an ideal point source, also the application of the inverse square law of the distance can lead to a not negligible underestimation of the irradiation time. It is therefore considered precautionary to increase the calculated times by at least 20%. Our results suggest that even with this correction, significant underestimation of the irradiation time cannot be excluded; one method to easily verify that a proper UV-C dose has been delivered is to position photochromic UV-C dosimeters on any surfaces where there is doubt about the exposure.
Regarding the possible damage induced by UV-C on materials, it must be remembered that most of the organic based materials can become damaged if they are not properly protected to UV rays. This damage, called UV degradation, affects many natural and synthetic polymers including some rubbers, neoprene and polyvinyl chloride (PVC). With too much exposure, these materials can fade in color, lose strength, become less flexible and finally crack. Certain inks and dyes can be affected as well. This problem, called photodegradation or phototendering, causes objects like textiles, artwork and polymers to: change color, fade in color and produce a chalky surface. Not all materials become damaged by UV radiation. Many silicones are generally UV-stable, as well as acrylic and types of glass, etc. At the time of writing, damage to materials in the hospital environments due to UV-C light disinfection was not reported . We have recently initiated a study to evaluate the photodegradation of wooden furnishings and the damage induced on the synthetic leather of the upholstery of the CT beds and of the swab armchairs. To date, the repetition of 700 disinfection cycles (25900mJ/cm2) did not show any difference compared to the unexposed material. However, the study will be extended up to the delivery of 50000mJ/cm2.
The main limitation of our study is not to have decontamination measurements on biofilms in which the virus may be embedded. A specific study on the subject has already been activated to verify UV-C induced inactivation on different surfaces.