Review of microbial touchscreen contamination for the determination of reasonable ultraviolet disinfection doses

Abstract

Background: Touchscreens are usually microbially contaminated and can therefore act as fomites inside and outside healthcare environments. Due to the increasing use of such touchscreens and the growing awareness of infection risks, approaches that allow safe and automatic disinfection are desired. Ultraviolet (UV) irradiation, with its known antimicrobial efficacy, could achieve this goal, but should be executed with limited touchscreen degradation, disinfection duration, and energy consumption. It should also pose as little harm as possible to humans even in case of failure. Materials and methods: A literature search was performed first to identify the microorganisms most commonly found on touchscreens. Then, the 90% reduction doses (D90 doses) for the different relevant microorganisms and UV spectral ranges were determined from the literature, and irradiation doses are suggested that should reduce most of these important microorganisms by 5 log-levels. Results: The most frequent microorganisms are staphylococci, bacilli, micrococci, enterococci, pseudomonads and E. coli with small differences between hospital and community environments, if antibiotic resistance properties are ignored. The determined irradiation doses for a 5 log-reduction of the most frequent microorganisms are about 40 mJ/cm 2 , 80 J/cm 2 , 500 J/cm 2 and 50 mJ/cm 2 for the UV spectral ranges UVC, UVB, UVA and far-UVC, respectively. These doses are also sufficient to inactivate all nosocomial ESKAPE pathogens on touchscreens by at least 99.999%. Conclusion: Disinfection is achievable in all UV spectral ranges, with UVC being the most effective, enabling automatic disinfection within a minute or less. The much higher doses required in the UVB and UVA spectral range result in much longer disinfection durations, with the advantage of a reduced risk to humans. For all kinds of UV irradiation, the doses should be limited to reasonable values to avoid irradiating an already more or less sterile surface and to prevent degradation of touchscreen devices.

Disinfection of Transparent Screens by Side-Coupled UVA LED Radiation

“…Hitherto, none of the studies have reported even a single touch screen without microbial contamination. Staphylococci have always been detected [4].…”

“…Bacterial strains most often found on touchscreens-sorted by observation frequency-and their necessary log reduction doses. (Modified after [4]).…”

Photoinactivation of Staphylococcus carnosus on Surfaces by Irradiation with Blue and Violet Light

“…The non-pathogenic relative Staphylococcus carnosus was chosen as the test organism for this investigation because it exhibits a visible light photosensitivity similar to that of S. aureus [9] and it can be used without infection risk. This and the fact that Staphylococci can be found on almost any surface [10] are reason that S. carnosus was selected for this investigation. To draw a comparison and answer the question of which sensitivity of bacteria increases when irradiation is applied to surfaces, the existing data of irradiations in liquids from the literature (published by our group) with the exact same S. carnosus strain and the same culturing procedure were employed [11].…”

Investigation on Potential ESKAPE Surrogates for 222 and 254 nm Irradiation Experiments

“…Therefore, there is still a need to catch up with regard to suitable surrogates. For example, in a literature review, we found that touch screens in healthcare settings are contaminated with bacteria such as ESKAPE pathogens (Hessling et al, 2021a). Surrogates would now be desirable for the development and testing of suitable disinfection measures or devices, so that these tests could be performed without risk, e.g., at least partially outside the hospital or biosafety laboratory.…”