For a year now, we have been going through a health crisis affecting the whole of humanity.
This episode has undeniable impacts on the economy and health.
The coronavirus responsible for Covid-19 is today (mid-November 2020) responsible for 55 million contaminations and 1.3 million deaths worldwide.
According to the WHO, “…Covid-19 is caused by the SARS-CoV-2 virus, which is spread in the population mainly through close contact with an infected person. The virus can be spread when small liquid particles are expelled through the mouth or nose when an infected person coughs, sneezes, talks, sings or breathes deeply. These liquid particles range in size from large “respiratory droplets” to smaller “aerosols”.
VIDOC-19 can also be contracted when the virus enters the mouth, nose or eyes (Kwok, Gralton & MacLaws, 2015). This is most likely to happen when people are in direct or close (less than one metre away) contact with an infected person.
According to currently available data, the virus is spread mainly through respiratory droplets between people who are in close contact with each other.
Aerosol transmission can occur in specific contexts, particularly in crowded and insufficiently ventilated indoor spaces.
In addition, people carrying the virus can leave infectious droplets when they sneeze, cough or touch objects or surfaces, such as tables, doorknobs and ramps. You can become infected with the virus if you touch these contaminated surfaces (Kampf, Todt, Pfaender & Steinmann, 2020) and then touch your eyes, nose or mouth before washing your hands. »
In order to respond to this problem of contamination by contact, solutions quickly appeared on the market.
For this reason, we can find in the trade (marketplace, big brands, …) disinfection modules by UV radiation and more particularly UVC.
At Sanodev, we are experts in disinfection by physical processes and we develop product lines for professionals allowing surface, air or water disinfection thanks to the germicidal powers of UVC, especially on SARS-Cov-2 (Pendyala & al. 2020).
Therefore, when we saw products marketed for a few dozen euros, we wanted to analyze their effectiveness.
Almost) without a priori, we bought a model in a major national retailer for 39.9€ and decided to conduct a brief study to determine if and how the device can destroy pathogens.
To do this, we decided to proceed in three steps. We mobilized part of our team (optical R&D engineer, microbiology R&D engineer and innovation project manager) and we tested the self-proclaimed “LED UV sterilizer”.
The terms chosen are very important.
First of all, let’s come back to the “sterilizer”. It should be pointed out here that in terms of pathogen removal, there are several “levels” ranging from decontamination to sterilization.
It should be noted that pathogen removal is counted on a logarithmic scale. We talk about LOG.
The calculation is very simple:
1 LOG corresponds to a division by 10 of the number of pathogens or an efficiency of 90%.
2 LOG corresponds to a division by 100 of the number of pathogens or an efficiency of 99%.
3 LOG corresponds to a division by 1000 of the number of pathogens or an efficiency of 99.9%.
At 2 LOG and 3 LOG, we talk about decontamination.
4 LOG corresponds to a division by 10000 of the number of pathogens or an efficiency of 99.99%.
5 LOG corresponds to a division by 100000 of the number of pathogens or an efficiency of 99.999%.
At 4 LOG and 5 LOG, we talk about disinfection. There is no longer any risk of infection.
6 LOG corresponds to a division per 1000000 of the number of pathogens or an efficiency of 99.9999%.
At 6 LOG and +, we talk about sterilization. There is no more risk of infection.
But then, does this product which is sold as “LED UV sterilizer” remove 99.9999% of the pathogens? The answer is no, and the packaging even says so: “Kills 99.9% of viruses and bacteria”.
At best, we are therefore at 3 LOG and therefore at “decontamination” level and very (very) far from sterilization (factor 1000 in between).
Now let’s take a look at the second term of the “UV LED sterilizer”, i.e. “UV”.
The product manual refers to
sterilization decontamination using UVC and UVA.
UVA is a part of the light spectrum with a wavelength between 315 and 400 nm (i.e. just below visible light). UVA is present on earth through solar radiation.
Nevertheless, the literature shows us that they tend to slow down bacterial proliferation under certain conditions (Chamberlin and Mitchell, 1978; Fujioka and al., 1981; Gameson and Gould, 1985; Mezroui and Baleux, 1992; Gourmelon, 1995).
The idea of integrating them may therefore seem interesting even if they have little direct effect on the elimination of pathogens.
The most interesting radiation is that of UVC with wavelengths between 100 and 280nm and a germicidal peak at 254nm (Sarada and al. 2000).
Unlike UVA, UVC does not reach the earth’s surface because it is filtered by the atmosphere (and fortunately!).
They have a strong germicidal potential since they penetrate the cells and will destroy the DNA chains composing them, making them inactive (Darnella et al., 2004).
In the case of animals, they are responsible for the occurrence of cancer, and in the case of bacteria and viruses, they prevent replication processes and cause their disappearance.
UVC radiation is therefore of interest to suppress viruses and potentially coronavirus.
The lamps that can generate UVC can be of several types: xenon lamps, mercury lamps and … LEDs.
The problem at this stage is that efficient and powerful UVC LEDs are still very expensive and complicated to produce and it would be surprising to find models with significant power in a cheap product.
However, we have decided to subject the “sterilizer” and its various LEDs to optical tests to find out how effective they are.
We measured the spectrum using a spectrometer covering the UV and visible range, which allowed us to interpret the different radiation frequencies and to compare them with the effective frequencies provided in the literature.
Two types of LEDs are present in the device. These are the ones we have tested.
What we assumed is well confirmed. LEDs do not (almost) emit in UVC and certainly not enough to eliminate pathogens.
NB: The scale of results is logarithmic. It is a graduation in geometric progression. Each step multiplies the value by a positive constant. We use this scale because the difference between the two peaks is so large that with a linear scale we would not see the emission peak around 260 nm.
To support these initial physical tests, we also conducted microbiological tests.
We cultured Escherichia Coli bacteria, a type of bacteria known for its sensitivity, particularly to UVC.
Methodologically, the experiment consisted of depositing 50µl of Escherichia Coli suspension. This was followed by a treatment phase via the sterilizer. The deposit is then recovered in physiological water with 0.05% tween. 50µl are then spread on TSA medium (agar). The medium is then incubated 24 hours at 37°C.
Exposure under a UV lamp of wavelength 253.7 nm at 33 cm and a fluence of 2.75 mJ/s cm² leads to mortality in 300 seconds or 5 min (Sanchez-Navarrete et al., 2020). We have treated our bacterial cultures with the commercial UVC sterilization device.
The results corroborate our initial observations. The 15 min exposure (the longest recommended by the manufacturer) did not destroy the bacteria that developed on the medium. Bacteria that are very sensitive to UVC radiation.
Some resellers are surfing on the health crisis by promising sterilization decontamination treatments in a few minutes via products marketed at low cost.
However, these products are not effective.
In fact, they are often white-label products on which the brands simply put their logo and are packaged in attractive packaging.
The consumer is deceived. He thinks he is acquiring a system that will allow him to secure his everyday objects when he is not. The effect is doubly perverse.
Firstly, the object is not disinfected and therefore it can potentially be a vector of contamination for the user.
Secondly, it can contribute to giving a false image of safety to the user, who can then become more negligent by indirectly exposing himself to contamination.
The production and sale of this type of device is consumerism at its worst, i.e. manufacturing objects that are totally useless (because they are totally inefficient) and therefore have a maximum environmental impact (waste of resources, transport, etc.) for zero efficiency. The consumer is simply deceived.
Our recommendations :
Be careful. UVC disinfections are scientifically documented, effective and proven, but products sold in stores can be misleading.
Moreover, the use of UVC calls for vigilance. Their ability to break DNA bonds makes them particularly dangerous for humans (skin, eyes, …).
If you wish to purchase such a device, check 3 things:
The product must not let UVC radiation pass through during its operation (UVC is stopped by most materials including glass or transparent plastics).
LEDs or UV lamps should emit radiation with a wavelength between 100 and 280 nm.
The pathogen removal rate must be at least 99.99% to avoid the risk of infection (=disinfection).
It is recommended to trust the devices certified by independent laboratories (certification of the virological part and test report) and meeting the standards (e.g. EN 170, EN 14255-1, ISO 15858 ) but beware of the UVC mention “EU validated” on some products. It validates the principle of germicidal efficacy of UVC radiation but does not guarantee that the product in its context is validated (since the ability to destroy pathogens depends on distance, exposure time and fluence).
Chamberun CE.. Mitchell R„ 1978. A decay mode! for enteric bacteria in natural waters, p. 325-348. In R. Mitchell (éd.), Water Pollution Microbiology, Vol. 2, John Wiley & Sons, New York.
Darnell, Miriam & Subbarao, Kanta & Feinstone, Stephen & Taylor, Deborah. (2004). Inactivation of the coronavirus that induces severe acute respiratory syndrome, SARS-CoV. Journal of virological methods. 121. 85-91.
Fujioka R, Hashimoto H, Siwak E, Young R. Effect of sunlight on survival of indicator bacteria in seawater. Applied and environmental microbiology, Mar. 1981, p. 690-696.
Gameson D.J., Gould G., 1985. Bacterial mortaiity. In Investigation of sewage discharges to some British coastal waters, Part2, chap. 8.
Gourmelon Michele (1995). Etude de la lumière visible comme facteur limitant de la survie de Escherichia Coli en milieu Marin. PhD Thesis, Université de Rennes.
Kampf G, Todt D, Pfaender S, Steinmann E. Persistence of coronaviruses on inanimate surfaces and their inactivation with biological agents. Journal of Hospital Infection. 2020
Kwok YL, Gralton J, McLaws ML. Face touching: a frequent habit that has implications for hand hygiene. Am J Infect Control. 2015 Feb.
Malayeri, Adel & Mohseni, Madjid & Cairns, Bill. (2016). Fluence (UV Dose) Required to Achieve Incremental Log Inactivation of Bacteria, Protozoa, Viruses and Algae. IUVA News. 18. 4-6.
Mezroui N., Baleux B (1992) : Effets de la température, du pH et du rayonnement sur la survie de différentes bactéries d’intérêt sanitaire dans une eau usée épurée par lagunage.
Pendyala B, Patras A, Pokharel B, D’Souza D. Genomic Modeling as an Approach to Identify Surrogates for Use in Experimental Validation of SARS-CoV-2 and HuNoV Inactivation by UV-C Treatment. Front Microbiol. 2020.
Sánchez-Navarrete, J., Ruiz-Pérez, N.J., Guerra-Trejo, A. et al. Simplified modeling of E. coli mortality after genome damage induced by UV-C light exposure. Sci Rep 10, 11240 (2020).