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Dunedin Hospital shines the light on UV-C air sterilisation

When COVID-19 first emerged as a global threat in 2020, Dunedin Hospital’s Infectious Disease Physician Dr Brendan Arnold began investigating UV-C light as a method of air sterilisation.

He was conscious of the hospital’s ageing infrastructure. There are no negative pressure rooms which are considered the gold standard for isolation/infection control and provide at least 12 complete air changes every hour.

“Our rooms were never designed as isolation rooms. They’ve been retrofitted. We only have about four on each ward and the air changes in many of them are as poor as two or three changes per hour. Nowhere near the 12 that you would want. They were never designed that way, so you can’t exactly hold them to contemporary standards.”

Dr Arnold wanted to make the environment as safe as possible for medical staff who would soon be dealing with COVID patients. “You’ve got to do everything that’s feasible and pragmatic, within reason, to improve safety including preventing COVID transmission within the hospital. So we had a problem.”

He began by talking to ventilation engineers. “But the air handling units are very old machines in Dunedin. So even trying to make these machines work harder and suck more air … it just wasn’t going to work. Other hospitals have temporarily increased their air handling units, and they’ll probably burn them out a few years sooner than they otherwise would normally have. That wasn’t an option for us either.”

Upper Air UV-C at Dunedin Hospital

“So then we really started looking at these UV-C lights because they seemed to be a really useful solution, particularly in our situation of trying to retrofit technology into an old building. Although it sounds technical, it’s really just a light that gets put up on the wall and any electrician can do that in a few hours; it doesn’t take that long.”

UV-C light has been used in medical settings for over 70 years – mainly to treat tuberculous – but it’s proven most effective at killing off airborne viral pathogens such as influenza, measles, smallpox and SARS-COV-2, the virus that causes COVID-19.

UV-C lights are mounted high on the wall or ceiling and emit light to the upper zone of the room, killing virus particles as they circulate. It works because UV-C radiation does not penetrate earth’s outer atmosphere, so bacteria and viruses have evolved without a defence against UV-C.

When used in this way, UV-C is not harmful to human health and there’s only minimal transmission to the skin’s epidermis (unlike UVA and UVB). But UV-C light does penetrate the cell wall of microorganisms and disrupts its DNA or RNA structure – essentially killing the virus.

“As long as basic precautions are taken in the design, setup, commissioning and maintenance of these lights, it is a very safe technology,” Dr Arnold says. “The lights are designed to be up high and they have little louvers on them so the light comes out horizontally. So you have a ‘kill zone’ or a sterilisation zone above our heads, while people are not exposed in the lower part of the room. It’s a proven way to significantly reduce the build-up of infectious particles.”

“As long as basic precautions are taken in the design, setup, commissioning and maintenance of these lights, it is a very safe technology”

By January 2022, Dunedin Hospital had installed around 20 UV-C lights in their respiratory wards and their emergency department observation rooms, with more on the way.

Dr Arnold considers the lights to be an important ‘layer’ in the hospital’s defence against COVID-19 transmission, along with portable HEPA filters with U-VC, PPE and social distancing protocol.

“It’s reassuring to know the air is being continuously sterilised all the time. That being said, UV-C will not block close range transmission. If I had COVID, and I came and coughed directly in your face, the particles haven’t had a chance to float up into the upper room and get sterilised. So the only thing that prevents that is mask use and social distancing, etc. There’s no one solution.

“We always hedge our bets in infection control. We rely on multiple barriers of protection. And so in the rooms that we have got UV-C lights, we’ve also put in a portable HEPA filter (air purifiers) with U-VC as well. In many ways that’s reassuring, in case the bulb blew in the light and no one noticed – well at least we’ve got a portable HEPA filter with U-VC going as well. Or if someone turned the HEPA filter off – at least we’ve got the UV-C light going. So the two work hand in hand quite nicely. And the HEPA filter also helps stir up the air so it rises into the UV-C kill zone.”

UV-C lights are completely silent and require minimal maintenance – just a light bulb change once a year.

The arrival of Omicron has strengthened the case for UV-C lights even further as it’s almost impossible to distinguish who is infected and who’s not, and keep them separate within the hospital. “We simply won’t be able to identify everyone at the front door,” Dr Arnold acknowledges.

“Part of living with COVID is to improve the sterilisation of air throughout the whole hospital so at least we’ve mitigated the risk of further transmission as much as we possibly can.”

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