AIRBORNE INFECTION CONTROL
Before closing, Professor Noakes said she would touch on two other technologies. She said: “There is a group of technologies based around charged particles – ionisers and plasma-type devices which distribute them around the room, and an electrostatic precipitation device, which uses electrostatics within the unit. The jury is out a bit on the effectiveness of these, although a study in Leeds showed the one we tested reduced Acinetobacter infections, and there is another one demonstrating a reduction in TB transmission. However, our study showed no effect on MRSA transmission, and that while the devices reduced microorganism prevalence in the air, they increased on surfaces. It’s quite likely there is a preferential charging, and then it creates the deposition. It’s possible – although hard to be certain – that there is a biocidal effect, and some of these devices can produce secondary pollutants, such as ozone.”
Chemical-based devices Also available were chemical-based devices that used some form of chemical oxidation. Some produced ozone, while others went through several cycles to generate hydroxyl radicals. While ‘pretty effective’ biocidally, Prof. Noakes said the biggest challenge was the secondary pollutants emitted, such as ozone, formaldehyde, or ultrafine particles – all respiratory irritants. There were also a number of chemical spray devices available, but the Professor felt none were currently suitable for use in occupied spaces, because of the potential accompanying secondary risks. She cautioned: “Also, be careful about what’s in a device (Table 1). In one set of
tests we did at Leeds with ioniser devices, all the units incorporated HEPA filters, as well as ionisation. We tested them both with the ionisation ‘on’ and ‘off’, and then removed the filters, and saw really quite dramatic differences, suggesting that the ionisation was not really contributing much. There will be a raft of technologies in some of these devices, and it may not be any of them other than the HEPA filters that are doing the work.”
In conclusion
In conclusion, Prof. Noakes said: “So, if you want to use an air cleaning devices, firstly decide whether you need it, or if you can mitigate your risks with something else. Secondly, consider what transmission routes you are mitigating – is it just the air, or are you trying to look at surfaces, something that is close to an aerosol source, or a little further away, and identify whether the device will do it sufficiently quickly to make a difference? Also, what is the device’s principle of operation, and can you discover this from the manufacturer’s literature? Equally, see what kind of evidence is available; how was the device tested, and is it claiming 99 per cent reduction in every circumstance, or just a particular one?, and is it relevant to the circumstances you will use it in? A device that works very well in an unventilated 20 m3
chamber
may not work as well in a 200 m3 ventilated hospital ward.”
One should also, she noted, consider the other impacts from the system – for example, would it affect comfort, or cause draughts, will it be noisy, or consume a lot of energy, and what are the secondary pollutants, and do they have health effects? Prof. Noakes said: “Ask yourself
what people will do with this technology – will they use it well, or will it influence their behaviour? Equally, what will you need to invest financially in the equipment, and the ongoing costs, and how will you meet those? Can you design and install an air cleaning system yourself, or do you need specialist input, and will your staff and perhaps also patients, need to be trained to use it?”
Location
The siting of the air cleaning system could also be key – would you choose an installed, or a portable device that people could potentially trip over? She said: “Also how are you going to maintain it. So, there are many elements to consider; it’s not simply a case of ‘buy one, plug it in, and hope for the best’. There are some excellent air cleaning devices out there, but also some poor-performing ones, but none of the systems is a ‘magic bullet’; always treat what you see with a little scepticism.”
With that, Professor Noakes concluded, thanked those whose work appeared in her slides, and said she would now take questions. Chris Davies then thanked her for her presentation, commenting that it had included ‘some really interesting pieces of research’, and provided plenty to think about for healthcare engineers and others with a professional interest in hospital air quality and ‘cleanliness’.
Acknowledgments
Professor Noakes thanked the following for their input into her presentation: Dr Azael Capetillo; Dr Carl Gilkeson; Dr Louise Fletcher; Dr Andy Sleigh; Dr Amir Khan; Dr Marco-Felipe King ; Laura Picking, and SAGE EMG.
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April 2021 Health Estate Journal 31
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