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Airborne infection


can damage skin and eyes. Devices come under the UK AOR regulations (2010) for workplaces and devices should allow no direct exposure without protection. UVC works through a biological inactivation


mechanism. It damages the DNA/RNA to form dimers and prevent replication. It inactivates but doesn’t remove microorganisms. Some can repair in visible light if the dose is sub-lethal (photoreactivation). The impact depends on the wavelength and microorganism. Factors affecting UVC include lamp position,


air velocity profile, reflectivity, lamp output, air temperature, relative humidity, and the microorganisms involved. Cath Noakes explained that the microorganism susceptibility depends on the type and species and climatic conditions – it is harder to inactivate microorganisms at high humidity. Therefore, if using UVC for infection control, it is important to understand which microorganisms you are targeting. “If you are targeting respiratory viruses, E.coli, and MRSA then UVC is quite good. If you are dealing with hardy fungal spores, it may not be as effective. There are different approaches to UVC. These


include: l Installed recirculating l Portable recirculating l Upper room GUV l Whole room Far UV


There are also disinfection units for use in unoccupied rooms – these are for decontamination rather than in room applications. Enclosed units are safe as there is no


exposure to UV. They are easy to install and can perform in a similar way to filter units, but they can sometimes be noisy depending on the design of the system. Upper room units are silent, offer potential for very high air-changes- per-hour (ACH) of 20+, but need sufficient ceiling height and no obstructions. The occupant exposure is low if they are designed correctly, said Prof. Noakes. She went on to discuss types of studies and approaches to evaluate effectiveness, but also cautioned delegates on the need to understand and interpret the effectiveness data that manufacturers disclose. Things to


consider include the test conditions, such as the following: l The microorganism species used l Room ventilation, rate and strategy – or no ventilation.


l Temperature and humidity l Size of room – smaller rooms give better results


l Device technology/device location l Sampling technique – decay or steady state, variability.


There are some real-world data to support the effectiveness of UV 1-3


to set up such studies. But what about Far UVC? Does this new


technology work and is it safe? Prof. Noakes explained that KrCl lamps emit primarily at 222nm and inactivate viruses on surfaces and air. In terms of its safety profile, there is evidence to suggest that, when KrCl lamps are filtered to remove longer-wavelength ultraviolet emissions, they do not induce acute reactions in the skin or eyes, or delayed effects such as skin cancer. So, could this be adopted as a whole room method for mitigating transmission? While there is laboratory evidence for Far-UVC


efficacy, there is limited evidence in full-sized rooms. Prof. Noakes and colleagues at the Universities of St Andrews and Dundee have set up room-sized chamber experiments to analyse the effectiveness of the technology – taking samples from the air and from surfaces. They used Staphylococcus aureus as the microorganism and performed air sampling and plate sampling. They also performed some measurements of ozone under different


but it can be challenging


ventilation conditions. The initial results were impressive, and the


team were surprised at how effective the technology was at reducing the concentration of Staph. aureus in the air. “We continually put Staph. aureus into the air, so the decline we saw wasn’t simply the decay. We saw a 92% reduction,” said Prof. Noakes. “This is the equivalent to an additional 35 air changes per hour and would outperform a portable air cleaner…This was spectacular and, at first, we questioned the results, so we carried out another set of experiments, looking at how it performs under different ventilation rates. Again, we saw reductions of over 90%, so we are getting really good inactivation. Other people from around the world are seeing the same effects.” The data indicate that Far-UVC is likely to


be more effective against common airborne viruses, including SARS-CoV-2, than bacteria and should be an effective and “hands-off” technology to reduce airborne disease transmission.4


While the results were impressive,


Prof. Noakes questioned whether there might be a ‘catch’. “We were concerned that it might produce ozone. So, we conducted some tests. If we have one lamp, or five lamps at a low intensity, the ozone is not much – just marginally increased over background levels. However, when all of the five lamps are going on in the room, we can have quite a substantial amount of ozone in there. It is not huge amounts, but notable. “There is international interest in this


technology. It has some potential, but we need to understand more about this trade-off


We continually putStaph. aureus into the air, so the decline we saw wasn’t simply the decay. We saw a 92% reduction. This is the equivalent to an additional 35 air changes per hour and would outperform a portable air cleaner. Professor Cath Noakes, Leeds University


. 18 www.clinicalservicesjournal.com I December 2023


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