UVC: Examining the efficacy of the emerging disinfection technology

1 iStock/AVAKAphoto

Gabriele Messina and Gabriele Cevenini of the University of Siena explore the emergence and efficacy of UVC disinfection technologies.

The onset of the COVID-19 pandemic brought with it an unprecedented flurry of new disinfection technologies, most notably those using UVC. For over 10 years, the University of Siena’s Gabriele Messina and Gabriele Cevenini have been collaborating synergistically in research activities focused on the engineering of disinfection techniques with classical (lamps) and innovative (chips and LEDs) UV sources. Here, they speak to Health Europa about the upsurge in UVC disinfection devices and consider some of the key advantages and limitations of these emerging innovations.

There is a lot of talk about UVC air disinfection systems as a valuable tool for combating the spread of viruses. But do these systems really work?

Every technology should be used with its limitations and advantages in mind. UVC is an effective and fast physical means of disinfection, with advantages and disadvantages compared to chemical disinfection. The main advantages are that UVC does not pollute, is practically effective on all micro-organisms (even those resistant to antibiotics and chemical agents) and is generally a good compromise between cost and effectiveness. The main disadvantages include the potential danger to humans and its inability to overcome obstacles between the source and the objects/elements to be disinfected.

What are the criteria for choosing an effective UVC air disinfection system?

The power of the UVC sources is very important, but the engineering of the systems is fundamental. It can make the difference between an ineffective system and a highly effective one. Those who have been manufacturing these devices for years know the elements that need to be considered to produce effective and safe systems.

UVC disinfection on air is based on two main principles: UVC rays contrast the ability of microorganisms to replicate; the exchange of outlet contaminated air and the inlet of fresh air dilutes the concentration of microorganisms in the environment. It is incorrect to use the word ‘sterilisation’, as the main mechanism of action of UVC, as just said, is not to ‘kill’ microbes, but to make them unable to replicate.

We often see advertisements for very cheap air disinfection systems and others that are more complex and expensive. What suggestions do you have for those considering the purchase of these systems?

It depends on what the purpose of the systems is, i.e., whether they have to work in the presence or absence of people and in a short, medium, or long space of time. Undoubtedly, there are many air disinfection systems on the market today, some of them extremely cheap. The main difference is their effectiveness, which depends inversely on the economic cost. The cheap ones have rather long air disinfection times (even several hours) during which there must be no people present or openings to contaminating external environments. Decontamination of environments in the presence of people and in a relatively short time (several minutes) generally requires very powerful systems and therefore very high costs: the latter can only be reduced through a high level of engineering optimisation.

We read that the main vehicle for spreading the COVID-19 virus is 90% aerosol. Is it more efficient to disinfect the air or surfaces to reduce the risk of infection in enclosed spaces?

Viruses are transmitted in many ways: by droplets emitted from the mouth and nose of an infected person, but also by contact. Although the SARS-CoV-2 virus is generally more transmissible by aerosol, transmission depends on many factors, such as distance, good hygiene practices such as hand disinfection, use of personal protective equipment (masks, gloves, etc.).

Hands are undoubtedly the main means of transmission of infections and, even if directly protected from airborne infections, their contact with a contaminated surface and subsequent contact with the nose or mouth, which is common in daily life, can be risky.

What benefits in terms of lowering the risk can the constant use of an air disinfection system in a closed environment provide?

A system that has been tested and shown to be effective in bringing down high levels of viral load is not necessarily able to provide risk reduction if not correctly contextualised. To explain it better, we can make the following example: a system that moves 10 m3/h of air in a room that has an air volume of 60m3 takes six hours to treat ‘static’ air that is present in the room. Even assuming that the passage of the treated air reduces the concentration of an airborne virus by more than 99.99%, the problem is that it takes time to pass it all through and any faster external contaminating action, even inadvertently, would drastically reduce its effectiveness.

The main mechanism of action of UVC is not to ‘kill’ microbes, but to make them unable to replicate iStock/AF-studio

Another consideration is that these tests are often carried out in controlled environments, where a known concentration of an aerosolised virus is placed, to verify the effectiveness of the system (i.e., the ability to inactivate viruses). In reality, these controlled tests do not take into account the fact that the system will then be used in a completely different context: the contamination that occurs in an environment in which there are subjects is not a fixed quantity from which the proportion of what is treated by the system is progressively subtracted; there is in fact continuous contamination by the subjects present in the environment. In the example above of the 60m3 room, it is only in theory that it takes six hours to completely eliminate the contamination. In reality, zero will never be achieved: the presence of even one person would make this unfeasible. The system will have some effect, but in practical terms, the size of the room and the continued human contamination will make it unlikely that a significant reduction in risk will be achieved. For the static disinfectant efficacy of the system to be effective even in a dynamically contaminated environment, we must act on the flow rate of treated air in the unit of time. In order to significantly reduce the risk, it is therefore necessary to have more powerful and imposing systems with a high technological level, the economic cost of which is even 10 to 100 times higher than the cheapest ones.

To better understand this statement, we need only think of operating theatres, where, in order to minimise the risk of patient infection, in addition to clothing, masks and means to prevent environmental and human contamination by operators (surgeons and auxiliary staff), we have impressive systems that guarantee 15 to 20 air changes per hour. Considering that a standard operating room is about 90m3, it is easy to see that there is a complete air change in about five to six minutes. The air that is introduced into the room also passes through High Efficiency Particulate Air (HEPA) filters which are able to retain particles of 0.3 microns, even though they are subjected to very high air pressures and flow rates.

From here you can see how, in a less ‘severe’ setting than an operating room, the appropriate system must be considered with reference to: the volume of the environment, the number of occupants, the possibility of ventilation with fresh and clean air from outside.

In a nutshell, a truly effective and efficient system must be able to reduce the risk in a real context and with the presence of people. However, even with the most powerful and efficient systems, when it comes to protection against SARS-CoV-2, indoors, it is still advisable to take the classic precautionary measures, i.e., hand hygiene, masks and spacing.

Does an air disinfection system combined with the use of masks totally eliminate the risk of contracting the virus?

The word totally is never fully usable when dealing with pathogenic microorganisms/viruses. Certainly, systems with a good UVC system, capable of quickly treating the ambient air in combination with effective masks allow to reach a rather high-risk reduction, substantially able to make contagion unlikely, especially if further precautions are taken related to the sanitation of environments and hand disinfection.

If these devices are effective in combating the spread of the virus, why have they been so little used and widespread?

Mainly due to lack of culture, lack of sensitivity and lack of vision. A chapter of a book could be written on each of these shortcomings. In extreme synthesis: the culture of hygiene as an element of primary prevention (preventing the transmission of disease and illness) is unfortunately not widespread and only because of the pandemic has made a strong comeback.

Most of the time, it is not understood that prevention is better than ‘fighting’ and curing.

Moreover, prevention needs investment and training (which do not come about by themselves, and which also require long-term investment) if it is to work. It also needs a vision that goes beyond the contingent problem of the individual moment. It should be planned strategically.

Unfortunately, we live in a context where everything is expected to be done at once, where the problem is tackled only when it arises (by investing, and mostly little and badly because we are not adequately prepared). Obviously, this hit-and-run approach cannot guarantee results. We should change our vision.

Some are doing just that. It is enough to look at the USA, where these technologies, assessed on an evidence-based basis, in a different health system from ours (health insurance companies) have been shown to save money, reduce care-related infections (which are very costly in treatment) and reduce mortality. Such UV equipment requires careful engineering and the necessary radio-photometric and microbiological tests and reviews, even in real-life environments, i.e., laborious, complex, and costly processes, the time needed to guarantee its effectiveness can be several months.

With the large increase in the number of vaccinations, it is still appropriate to think about using UVC air disinfection systems?

Absolutely. Our guard should never be lowered. Perhaps if we had more of a culture of prevention, efficient technological means (e.g., valid tracking systems, predictive mathematical models to support correct and rapid decisions, etc.) to combat the pandemic, it would not have spread so vehemently. We need to spread the culture of primary prevention, in order to prepare ourselves to nip in the bud, or at least to fight more effectively and quickly, the next possible pandemic emergency.

Are there any risks in using air disinfection systems with UVC lamps?

There are, but they are nil or negligible if the systems are carefully engineered and certified, especially in terms of safety. In fact, the high power of UVC lamps would cause serious damage to human health if their radiation were accidentally directed for even a few seconds towards the skin or, worse, the eyes. The problem of mercury in UVC lamps and their possible production of ozone, both of which are toxic and dangerous to human health, can also be well addressed and safely contained.

Does disinfecting the air with UVC lamps 100% replace the need to change the air in a room?

No. Air exchange is still recommended. Remember that these systems reduce the risk at different levels, but never completely eliminate it. Any other simple action to make the air fresh and clean should be considered, regardless of whether or not a technological disinfection system is used.

With an air disinfection system, could a shop accommodate more people than allowed under recent regulations?

In principle this would be possible, but it is difficult to quantify exactly how many people can occupy an enclosed space of a certain size with a disinfection system in action, without precise tests. In addition, the recent regulations are moving in the direction of reducing the risk of infection, but not eliminating it completely.

Therefore, the answer is yes, but only if the device has been thoroughly tested and certified for such situations by reliable bodies. Otherwise, it is strongly inadvisable. Giving false assurances is more harmful than managing the risk itself.

Is there anything else you would like to add?

In our university experience of research, development, innovation and technology transfer, we have supported and are still supporting many companies with their products. We take them at different levels of design, and we always try to give them a rigorous scientific label, proposing innovative solutions.

We involve companies in this process, making them part of and aware of the various stages of technical development and testing, including the recognition of product limitations, with particular attention to the economic cost and the commercial values that can be generated.

Lastly, we do not just carry out laboratory tests for compliance with the regulations in force, but go as far as to carry out real, concrete tests on the actual field of application.

In conclusion, we would like to summarise our opinion briefly by saying that today’s technological systems based on UVC light, but also UVB, UVA and even in the visible range close to UV (near UVA), are valuable and powerful aids in the fight against infections, epidemics and pandemics. However, they must necessarily be accompanied by careful design, correct use and sizing of the disinfectant light sources for specific applications, and, above all, they must have undergone serious and accredited technical-scientific testing of their biocidal performance, both in controlled laboratories and in real use environments.

We therefore recommend the use of UV-based technological systems that are associated with these characteristics and are accompanied by documentation/certificates issued by agencies or institutes accredited by governmental bodies.

Gabriele Messina
Professor of Public Health
University of Siena

Gabriele Cevenini
Professor of Biomedical Engineering
University of Siena

This article is from issue 19 of Health Europa Quarterly. Click here to get your free subscription today.


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