Reducing Viruses in Clinic Air

By Mike Murphy / 08 Feb 2021

Physicist and bioengineer Mike Murphy explains how to reduce the presence of viruses in your clinic’s air through UV light energy

The COVID-19 virus is in the air. It has long been known that the common cold and the flu are more readily caught during the winter months. This is because people tend to stay indoors for longer periods compared with the warmer months. It is also because the virus ‘sits’ on aerosols in the air that we breathe if there is an infected person shedding viral particles nearby.1

The possibility of COVID-19 cross-infection through aerosols has been discussed since March 2020.2 Authors have pointed out that this method of transmission appeared to explain some infections in Mongolia and Wuhan, where direct, physical contact had been ruled out. They also indicate that other research has proven that the SARS-CoV-1, MERS and H1N1 viruses are known to spread via aerosols, as supported by other authors.3 Influenza viruses and rhinoviruses are also well-known to spread via aerosols.1

The well-established case of the Diamond Princess, a cruise ship that was docked in Yokohama in March 2020, appears to show how easily an aerosolised virus can spread. 712 people became infected on that ship, even though many were quarantined in their cabins. Cruise ships employ ventilation, but they do not routinely use high efficiency particulate absorbing (HEPA) filters, which are discussed below.

With the new UK COVID-19 variant becoming more prominent in the UK, which is more infectious than its predecessor, it’s more important than ever to consider your clinic’s air quality.4

How viruses enter and stay in the air

Bioaerosols – aerosols containing potentially hazardous biological materials – may contain components in the size range 1 to 5 microns. Expelled saliva droplets created through speech, coughing or sneezing may be mostly between 1-5mm (1,000-5,000 microns), but these generally fall to the floor, and other surfaces, within a short distance of the exhaler, typically 1-2 metres.1 These may contain viral particles which can remain active on surfaces for days, particularly hand-sanitising equipment.5 However, smaller droplets carrying virus particles can form either during exhalation, simple speech or shouting and singing, or via evaporation, generating aerosol particles. These are easily carried on air and thermal currents and can be distributed around a room in a short time, creating an invisible ‘cloud’ of virus-laden droplets (Figure 1).5

It is known that viruses may be contracted through mucosal areas – nose and mouth – and conjunctiva – the eyes.6,7 Consequently, we should not only wear masks to minimise exhalation of virus particles, but also eyewear to minimise contracting viral particles through our eyes. Even ordinary spectacles will offer some barrier to airborne particles.8,9

A very interesting study looked at the importance of respiratory droplet and aerosol routes of transmission from ‘seasonal’ coronaviruses (this study was carried out before COVID-19 emerged), influenza and rhinoviruses.10 They measured the amount of exhaled respiratory virus particles from 246 infected patients, half of whom were wearing face masks, while the other half were not.

They found that patients with influenza were more than twice as likely to exhibit fever symptoms and temperatures greater than 37.8°C, compared with coronavirus and rhinovirus patients. They also observed that coronavirus patients coughed much more than the other patients, thereby increasing the likelihood of generating virus-laden aerosols.

However, their most important observation was that coronavirus patients who did not wear face masks generated detectable respiratory droplets and aerosols from their exhalations. Those patients who did wear face masks generated virtually no detectable coronavirus-laden respiratory droplets or aerosols.

The same conclusions were made following a meta-analysis of 172 observational studies from 16 countries.11 This report, in The Lancet, found that the wearing of face masks 'could result in a large reduction in the risk of infection’, with a higher protection level with respirators (N95, FFP2 etc.). They also noted a lower level of infections when eye protection was also used.

There are many other publications which highlight the increased infection rates associated with aerosols.12-16 Lu found that the peak of infectivity of COVID-19 occurred one day before symptoms became obvious and that around 70% of all viral transmissions occurred during the incubation period, which had a median of around 11.5 days.17 This suggests that most people are being infected by carriers who are unaware they have the virus, and before they exhibit any fever symptoms such as high temperatures.

Understanding infectious dose

‘Infectious dose’ is an important parameter. This is the average number of viral particles needed to infect a person. Infectious dose is related to the concentration of viral particles in the air (and on surfaces). Clearly, the viral concentrations are higher in smaller rooms, or when there are more people in a room, rooms with poorer ventilation, and if more time is spent in a room (assuming an infected person is, or has been, shedding in that room). The infectious dose for COVID-19 is likely to be “In the region of a few hundred or thousand particles,” according to microbiologist Professor Willem van Schaik of the University of Birmingham, England.12

Many people often confuse ‘infectious dose’ with ‘viral load’. Viral load is the concentration of virus in the blood, not the air, and determines the progression of an illness in individuals, but a person with a ‘high’ viral load is more likely to shed more viral particles.12

A report from Ryan indicates that ‘medium’ to ‘high’ doses of SARS-CoV-2 can result in severe illness, while a relatively low dose may, or may not, induce illness.18 They also found that low doses of the virus typically resulted in a milder level of symptoms, compared with the higher doses. This clearly indicates that minimising potential exposure is paramount in reducing the probability of developing any symptoms.

The same results were found in an earlier study of the influenza virus.19 The authors found a clear relationship between the infectious dose of influenza and the final outcomes of patients. People exposed to ‘high’ doses were much more likely to become ill, compared with those that only received a relatively small dose.

Swedish scientist Per-Arne Torstensson has calculated that around 80-90% of all COVID-19 infections probably result from inhaling virus-laden aerosols, thereby increasing the need for a comprehensive approach to reducing such risks.20 This calculation is supported by research from Australia.21

It has long been known that ordinary breathing and speech can result in the exhalation of a large amount of aerosol particles.22 In fact, a 10-minute conversation with an infected, asymptomatic (or presymptomatic) person, speaking normally, can generate an invisible ‘cloud’ of around 6,000 aerosol particles, which are potentially virus-laden. These particles will distribute throughout a room within minutes and may linger for many hours if there is no attempt to clean the air.22

The newly discovered mutated COVID-19 strain, first identified in England in late 2020, is around 70% more transmissible, according to UK government authorities.4

This is likely due to infection occurring from a lower infectious dose than with the previous strain. A recent article looked at the spread of COVID-19 in 10 of the largest cities in the US, using computer modelling. They found that more than 80% of infections likely occurred in restaurants, bars, gyms, cafés, hotels and religious establishments – locations with high densities of people. It is most likely that many of these places do not employ good ventilation/filtration and/or ultraviolet cleaning (UVC) systems.23

Cleaning the air in your clinic

To reduce the risk of infection from airborne viral particles we need to ‘clean’ the air. Apart from using a simple air-spray containing an anti-viral solution, this may be done in a number of ways.

Increased ventilation

As mentioned, colds and the flu spread much more readily in the winter months because we all spend much more time indoors or in enclosed spaces with closed windows i.e. much less ventilation than during the warmer months.24 As a result, we breathe in more contaminated air, resulting in more infections. However, we don’t really want to open windows when it might be near freezing outside, so this may not be the first option in many situations!

Filtration systems using HEPA/ULPA filters

A simple way to reduce air contaminated with unwanted airborne particles is with the use of appropriate filtration systems. High efficiency particulate absorbing (HEPA) and ultra-low particulate air (ULPA) filters can filter airborne particles down to 0.3 microns with a 99.95% efficiency in Europe (99.97% in the US), and 0.1 microns with a 99.999% efficiency, respectively.25 These are standard issue in many hospitals and ‘clean room’ facilities but are not routinely used in many clinical/aesthetic settings.

To illustrate the effectiveness of these filters, the 10-minute conversation generating 6,000 aerosol particles, discussed earlier, would be reduced to less than two particles with a HEPA filter and zero particles with an ULPA filter.

Even floor-mounted, portable air filtration systems would add an extra layer of protection. However, the filters need to be removed and disposed of as ‘infectious clinical waste’ since they are potentially very hazardous, as they may contain significant numbers of active viral particles. Such systems appear to be relatively easy to source and the cost varies from a few hundred pounds to many thousands, depending on size and requirements.

Ultraviolet light cleaning

UVC light is composed of high-energy photons which are not particularly safe for tissues since they can alter cellular DNA/RNA, leading to mutagenicity.26 Consequently, high intensity UVC light should not be openly used routinely in the same space as humans, or any other living creatures.

A recent study has demonstrated very clearly that the use of far-UVC (207-222 nm) can effectively increase disinfection rates in ‘typically ventilated’ rooms by a factor of between 50-85%.27 This suggests that rooms should be cleansed by UVC light while empty – perhaps overnight when those rooms are not usually occupied (see Figure 2). Alternatively, ‘self-contained’ units which do not allow the light to spill out into the local environment may also be used. A Danish company has developed such units called the Sanispace device, which draws room air through a sealed unit and may be active continuously, even while the room is occupied. Other systems include the UV CleanLight, Energi Vac and the Woodpecker units. Such units might be ideal for clinical/aesthetic settings where relatively high numbers of people may ‘pass through’ each day. At the time of publishing, these units vary between around £500 and £3,000 per unit.

Various floor-mounted devices are also available from around the world, but many of these are not suitable when people are present, since they output high doses of potentially harmful UVC into the environment. Examples of such systems include the VioUV device from the US, and the Camlab unit or the Germiled device, both from the UK. Again, such systems range in price from a few hundred to a few thousand pounds.

‘Upper room’ UVC systems have been in wide use for many years. These units are typically placed at a height of two metres or higher and emit UVC in an upward direction to create a high-intensity zone in the upper part of a room, while minimising the dose in the lower part of the room, which may be occupied.28

UV light has proved useful in the reduction of active coronaviruses in the air and on surfaces.28,29,30 One study reports that hospitals in China have been instructed to run UVC lamps for one hour, three times a day, every day.8 The author recommends that increased ventilation, even via open windows, more sunlight and that UVC lamps should be routinely used in hospital settings. Recently, the University Hospitals of Derby and Burton have installed ‘robotic’ UVC devices which autonomously roam through wards, theatres and corridors, during quiet times.31

Dr Ewan Eadie of the University of Dundee, has stated, “UVC is proven to inactivate viruses and bacteria and has been used for the past 90 years for this purpose. When deployed appropriately in the ‘real-world’ it can significantly reduce the risk of transmission from airborne viruses.”32

The evidence is clear that UVC is an excellent method for deactivating coronaviruses. While the above procedures may not remove viral particles completely, they can reduce the infectious dose significantly, which can only be a good thing.

Help reduce the spread

The simplest, most effective ways to reduce cross-infection of this virus are to wear a mask, at all times, and avoid crowded places (including public transport, sporting events etc.) until vaccines are widely available. Do not stay indoors where the risk of contraction is greater for any longer than absolutely necessary. The science is very clear on this. The Chang report clearly shows that crowded places such as cafés, restaurants, supermarkets and gyms, are all ‘high risk’ locations – this is simply because the air in such places is laden with virus particles on aerosols with poor ventilation.23

Aerosols form while breathing, speaking, singing and shouting. These aerosols can ‘sit’ on air currents for hours in poorly ventilated rooms. The air must be removed and/or cleaned using filtration, air sprays containing airborne anti-viral agents and/or UVC light. Asymptomatic and pre-symptomatic people can shed viable virus unknowingly for days before symptoms become obvious, if at all. Quite frankly, detecting a fever temperature in a carrier is too late – that person may well have been shedding the virus for days. New protocols should be introduced into clinics to reduce virus-laden aerosols and the probability of infecting patients/clients.

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