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Infect Prev Pract
Infect Prev Pract
Infection Prevention in Practice
2590-0889
Elsevier

S2590-0889(24)00054-4
10.1016/j.infpip.2024.100390
100390
Original Research Article
Evaluation of the antimicrobial effect of a far-uv radiation lamp in a real-life environment
Bansaghi Szava a
Klein Jörn Jorn.Klein@usn.no
ab⁎
a Faculty of Technology, Natural Sciences and Maritime Sciences, Department of Microsystems, University of South-Eastern Norway, Porsgrunn, Norway
b Faculty of Health and Social Sciences, Department of Nursing and Health Sciences, University of South-Eastern Norway, Porsgrunn, Norway
⁎ Corresponding author. Address: Faculty of Health and Social Sciences, Department of Nursing and Health Sciences, University of South-Eastern Norway, Porsgrunn, Norway. Jorn.Klein@usn.no
18 8 2024
12 2024
18 8 2024
6 4 10039028 11 2023
26 7 2024
© 2024 The Authors
2024
https://creativecommons.org/licenses/by-nc-nd/4.0/ This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Summary

Background

Using far-Ultraviolet-C (UVC) radiation with an emission maximum of 222 nm, has the potential to kill bacteria while not being harmful to humans and can be used continuously in public areas. Elevators pose a high risk of infection transmission, as they are small, crowded spaces with poor ventilation. In such a setting continuous decontamination would be very useful. This study aimed to measure the effectiveness of a far-UVC lamp installed in a frequently used elevator by comparing the bacterial load found in that elevator with the bacterial load in a control elevator.

Methods

Microbial load was measured by different methods; ATP bioluminescence, surface samples were collected by contact slides, contact plates, and swabbing. Air samples were also collected.

Results

No significant differences were found in the microbial content between the control elevator and the UV-lamp elevator, regardless of whether the UV-lamp was always on, or was used with a motion sensor to turn off when someone entered the elevator.

Conclusions

The results suggest that the far-UVC requires a longer time to kill the bacteria, while the people traffic were continuously re-contaminating the elevators.

Keywords

Far-UVC
UV-222
UVC-decontamination
Infection control
Environmental cleaning
Infection prevention
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pmcIntroduction

Ultraviolet –C (UVC) is radiation with a wavelength between 200–280 nm [1]. UVC has a strong antimicrobial effect, as it can lead to DNA damage by creating pyrimidine dimers and generating reactive oxygen species (ROS) [2]. UVC radiation has been applied for disinfection for almost a hundred years [3]. UVC disinfection offers several advantages, including minimal human intervention, absence of consumable requirements, and lack of waste generation. The main limitation of the usage of UVC radiation that it also damages human DNA and in extreme cases, it can contribute to carcinogenesis. Therefore, UVC can only be applied in areas where no one is present.

Traditionally the 254 nm UVC radiation, emitted by mercury vapour lamps was used for disinfection. Studies claim, that short-wavelength UVC light in the spectral region of 200–230 nm (far-UVC) can inactivate pathogens without damaging human cells, which might greatly improve usability [4]. A systematic review summarised over 100 scientific papers that examined the effect of far-UVC radiation and concluded that far-UVC, especially the 222 nm emission of KrCl lamps has strong antimicrobial properties, without harming human cells, if optical filters block emissions above 230 nm [1].

The advantageous characteristic of far-UVC radiation can be explained by its strong protein absorption, compared to traditional UVC radiation. The larger size of the cells compared to microorganisms also plays an important role. Less than 5% of far-UVC radiation reaches the center of a mammalian cell with a typical diameter of more than 10 μm [5]. Human skin is also protected by the outer layer of the skin, consisting of dead cells that absorb most of the radiation. In the case of the eyes, it is supposed that the tear layer and the cornea protect the lens. The review highlights, that the approach is very promising, but the data are still sparse, as most studies which suggest that far UVC is safe were conducted with the participation or support of a single manufacturer of far-UVC lamps (Ushio) and may not be considered independent. [1]. Independent studies could not help to verify the findings in previous studies but also can play a role in building confidence in the technology.

The likelihood of infection transmission increases with the number of people who are using the same area, especially when this space is small, poorly ventilated, and the surfaces are frequently touched. Elevators in crowded buildings fulfil all these characteristics. Most studies where microbiological contamination of elevators has been examined were carried out in a hospital environment. Kandel et al. investigated the prevalence of bacterial colonisation on elevator buttons [6]. They concluded that buttons were commonly colonised by bacteria (61%). Most bacteria were not clinically relevant and coagulase-negative staphylococci were the most common organisms cultured. Pereira da Fonseca et al. studied the diversity of bacterial communities and potential pathogens on elevator buttons [7]. They highlighted that the high degree of microbial diversity found at the surfaces of elevators may also be attributed to poor personal hygiene, as large a proportion of organisms were likely to have originated from faecal contamination. They concluded that the reduction in this contamination could reduce the overall infection rate.

This study aimed to measure the effect of the UVC (UV-222) lamp on the microbial loads in a real-life, non-hospital setting, in elevators at a university campus. Anticipated contributions of this study to the field of microbial control include providing empirical data on the effectiveness of far-UVC technology in everyday environments outside clinical settings. This is particularly relevant given the increasing interest in UVC as a non-chemical disinfection method in public spaces.

Methods

Experimental settings

UV-222 lamps were installed into two elevators on Drammen Campus of the University of South-Eastern Norway (USN). The Drammen campus was selected as that is one of the biggest campuses of USN, with approximately 3500 students, and the elevators were likely to be among the most frequently used in the University. There were three elevators next to each other in the main building of the campus (Figure 1). One of the elevators remained unchanged, while the other two elevators had UV-222 lamps with different settings installed in them.Figure 1 Elevators involved at the University of South-Eastern Norway campus, Drammen, Norway. The middle elevator (Elevator #1) remained unchanged, right (Elevator #2) and left (Elevator #3) elevators were equipped with UV lamps.

Figure 1

The elevators were OTIS ® Gen2 type elevators with maximum capacity of 13 persons. Internal dimensions were 110x210x220 cm (width x depth x height).

Sample collection was carried out between February and July 2023.

The Norwegian Ethical Committee confirmed that no ethical approval was required for the study (REK 576150).

UV lamps

The UV lamps for this study were supplied by UVMedico, a Danish UV lamp manufacturer. These germicidal lamps had a peak emission of 222 nm. From one meter distance, the total irradiance was 13.82 μW/cm2. Lamps had an optical band-pass filter that transmits 222 nm and blocks wavelengths longer than 230 nm. Wavelengths shorter than 200 nm were also suppressed, to prevent ozone generation. In the case of these lamps, more than 95% of the emitted light was between 200 and 230 nm. The manufacturer declared that the Germicidal Compact Far UV light is in conformity with the following directives and standards: 2011/65/EU, 2014/35/EU, 2014/30/EU, ISO 15858, IEC62471, EC PAS 63313 ED1, and ACGIH. For each lamp, an individual light measurement report was attached (Figure 2).Figure 2 Individual light measurement report of the lamp that was installed in Elevator #2. A: The report shows that the majority of the light emission is within the safe wavelengths, between 200 and 230 nm. B: Irradiation pattern depending on the distance from the lamp.

Figure 2

The UV lamps had different programs, as described in Table I.Table I Settings of the UV lamps used during the study

Table IMode	Description	
“Always-on” mode	The UV lamp was programmed to be on continuously between 06:00 and 23:00 every day, regardless of whether there were people in the elevator or not.	
“Motion-sensor” mode	The UV lamp was programmed to deactivate when someone enters the elevator, it therefore only works when the elevator is empty. The lamp is completely deactivated between 23:00 and 06:00.	

The lamps were installed at the upper-back corner of the elevators, directly under the ceiling, and directed toward the operating panel, located in the middle of the elevator. This arrangement ensured that light waves could reach all surfaces evenly without any shadow, also aided by the reflective surfaces (Figure 3).Figure 3 The installation of a lamp in the right elevator (Elevator #2). A: Shows the interior of the elevator, with an arrow indicating the position of the lamp. B: Illustrates the lamp in operation.

Figure 3

Elevator usage

Elevator usage was measured to be sure that all elevators were equally used. The elevators were automatically controlled; after pressing the button, the software decided which elevator would arrive. The left elevator (#3) was bigger than the others, the remaining two had the exact same interior. Traffic was counted on the ground floor (1st floor) where most people entered and exited from the elevator. During every hour, a half-hour period was monitored. The observation began on the hour every hour and ended half past, except for the first and last monitoring period (8:40–9:00 and 17:20–17:50, respectively), for logistical reasons.

ATP measurements

For measuring adenosine triphosphate (ATP) bioluminescence of surfaces, the ATP SystemSURE plus (Hygiena) device was used, together with UltraSnap swap. Bioluminescence was measured in relative light units (RLU). Based on the manufacturer's instructions, a 100 cm2 surface was sampled in each case [8].

Surface samples

To measure the microbial load of surfaces inside the elevators, several sampling methods were used. Table II contains a detailed description of the methods and the name as it will be referred to. Samples always were collected in pairs; one from the control elevator and the corresponding one from the UV elevator. The method chosen for each case was determined by considering the size and design of the respective surface.Table II Surface sampling method applied during the study

Table IIMethod name	Method description	
LabSlide	Labslide TV (Labolytic 10065) contact slides were applied. Slides had total germ agar on one side, and agar for Enterobacteriaceae on another. Sites referred to as “T” for total, and “E” for Enterobacteriaceae agar.	
Hygicult	Hygicult contact slides (Labolytic 10220) were applied, with total plate count agar on both sides.	
Contact plate	Contact plate (VWR C31114TI) made from Tryptic Soy Agar, also neutralizing agents included in the medium inactivate residual disinfectants.	
Contact slide	Contact slides (VWRb525272V), contains TTC agar.	
Transport s.	Samples were collected by transport swab (VWR 710–0438), previously moistened with 0.9% NaCl solution (R-Biopharm Z0301). Samples were plated at the lab to tryptone soya agar (TSA) plates (VWR P21114ZI) and incubated at 37°C for 72 hours.	
Polygon 10	3∗1 ml sterile 0.9% NaCl solution (R-Biopharm Z0301) was poured into a 50 ml centrifuge tube. The sampling swab (Propax polygon swab 71454–01) was moistened first, then the surface was rubbed several times. 10 μl of samples were plated onto tryptone soya agar (TSA) plates (VWR P21114ZI) and incubated at 37°C for 72 hours.	
Polygon 100	Same as before, but instead of 10 μl, 100 μl samples were plated.	

Air samples

Air samples were collected by using Sartorius BACTair ™ culture media (WVR SART14320-110-ACD). This media contains tryptic soy agar in an integrated disposable sieve. Two elevators were sampled, Elevator #1 (control), and Elevator #2, where the UV-lamp was set to “Always-on” mode. During the sample collection, only the researcher was present in the elevators. Before and after elevators were in regular use. Air samplers were positioned in the center of the elevator, at a height of around 50 centimeters from the floor.

Statistical analysis

Data were stored, and statistical analysis was performed using Microsoft Excel (Version 2308 Build 16.0.16731.20310). To compare the control elevator with the other elevator equipped with UV-lamp, two-tailed, paired t-tests were performed.

Results

Elevator usage

Elevator usage had a peak around 11 am, as shown in Figure 4. Usage was the same in the morning and in the afternoon. There was a decline in traffic after 5 pm.Figure 4 Distribution of elevator use during a day in the case of the three elevators. The same, half-hour period was measured in each hour, except the first and last period (see Methods section).

Figure 4

Traffic data also highlighted that while the middle and the right elevators were equally used, the left elevator (#3) had significantly less traffic (Figure 5). As mentioned earlier, elevator (#3) was larger than the other elevators. It was often occupied by cleaning trolleys and other maintenance staff, which may have explained the reduced traffic. As a result, we decided not to include data collected from elevator #3 in further analysis and only the samples collected from elevators #1 and #2 (the two elevators that were identical and had a similar usage pattern) were analysed.Figure 5 Elevator usage in the case of the tree elevators that were involved in the study. After getting these results we concluded to exclude Elevator #3 from further analysis and sample collection.

Figure 5

In addition, the UV lamp in the other UV-elevator was changed later from motion-sensor mode to always-on mode, and experiments were repeated with these settings.

ATP measurements

ATP measurements were taken on two different days, two months apart. When the UV lamp was in “Motion-sensor” mode, higher average RLU values were measured in the control elevator (Table III). When the UV lamp was in “Always-on” mode, the UV-elevator had a 7-times higher average RLU value than the control elevator. None of these differences were significant, probably due to the relatively low sample size.Table III Colony forming units observed in the case of surface samples collected from the two elevators

Table IIIDate	Sample No.	Sampling site	Sampling methods	Colony forming units (CFU)	P-value	
Elevator #1	Elevator #2	
Control	Motion sensor	Always-on	
Feb-15	#1	Rail	LabSlide T	1	15		0.419	
#2	Rail	LabSlide E	0	1		
#3	Wall	LabSlide T	21	0		
#4	Wall	LabSlide E	2	0		
#5	Mirror	Hygicult	2	0		
Apr-25	#6	Rail	Hygicult	32	32		
#7	Rail	Hygicult	19	35		
#8	Rail	Contact plate	25	43		
#9	Rail	Contact plate	73	75		
#10	Rail	LabSlide T	18	21		
#11	Rail	LabSlide E	11	2		
#12	Panel	Contact plate	169	12		
Total				373	236			
Apr-15	#13	Wall	Contact plate	252		5	0.955	
#14	Rail	Contact plate	100		60	
#15	Wall	Contact slide	7		2	
#16	Rail	Contact slide	35		52	
#17	Buttons	Transport s.	21		73	
#18	Rail	Transport s.	32		9	
#19	Wall	Transport s.	12		2	
#20	Rails	Polygon 10	7		25	
#21	Rails	Polygon 100	71		378	
#22	Buttons	Polygon 10	13		5	
#23	Buttons	Polygon 100	73		11		
Jul-18	#24	Rail	Contact slide	2		2	
#25	Rail	Hygicult	9		7	
#26	Rail	Hygicult	25		7	
#27	Panel	Hygicult	2		0	
#28	Panel	Hygicult	1		0	
Total				662		638	

According to the manufacturer's instructions [8], RLU value higher than 30 should be interpret as ‘dirty’. In the control elevator, half of the samples had RLU way more than 30, and additional two was near 30 RLU (25 and 28). That can probably be explained by the outstandingly high frequency of use, compared to other surfaces.

Surface samples

Surface samples were collected by several different methods and from different surfaces, but always in pairs; the same way in the case of the two elevators. Table III shows the details of the sampling site and methods. Table IV summarises the results. The exact location of each sampling site is marked on Figure 6. Large variability was found, and there was no clear trend that show one elevator would contain fewer microbes than others.Table IV Colony forming units (CFU) on air samples collected from the two elevators

Table IVElevator #1
Control	Elevator #2
“Always-on”	P-value	
Sample #	Sampling time	CFU	Sample #	Sampling time	CFU	
#1	60 sec	165	#2	60 sec	109	0.900	
#3	60 sec	317	#4	60 sec	199	
#6	90 sec	153	#5	90 sec	371	
Total		635			679		

Figure 6 Surface sampling site inside the elevator. Sample number can also be found at Table III, which provides detailed descriptions for each sample.

Figure 6

Air samples

Six air samples were collected, three from each elevator at ten-minute intervals. Figure 7 shows a sample image of the air sampling. Table IV summarises that an almost equal number of microbes were found on the two elevators, no significant differences were found.Figure 7 Representative images of the air sample collected in the control elevator and in the elevator equipped with the far-UV lamp.

Figure 7

Discusson

ATP measurements were inconclusive in this study and hence the results were not significant. Therefore, the data collection was not continued. Some studies have reported that when bacteria are killed by UV light, the level of ATP changes slowly. Xu et al. demonstrated that when E. coli was completely killed by 100 mJ/cm2 UV radiation, only an 8.56% decrease was observed in cellular ATP level, and similar values were found when the total ATP level was measured [9]. Another study described that ATP decreased so slowly that even 48 hours after the UV-treatment, part of the original bioluminescence was still detectable. The ATP concentration decreased in the UV-exposed E. coli to 47.3%, 33.5%, 22.9%, 14.8%, and 10.8% for UV fluences of 5, 10, 20, 40, and 80 mJ/cm2, respectively [10]. Based on these data, ATP measurements do not seem to be objective in measuring the effect of UV-decontamination.

The observed lack of significant differences in the number of colony-forming units (CFUs) on surface samples and the similar microbial loads in air samples from both elevators suggest several factors contributed to the results. These factors warrant further investigation.

The effectiveness of UV lamps in microbial reduction largely depends on their positioning and coverage. If the lamps were not positioned to optimally expose all surfaces and air within the elevators, some areas might have received inadequate UV light, leading to uneven decontamination. Also, the killing capacity of UV light reduces rapidly with distance.

The duration of UV exposure, coupled with the intensity of the lamps, are crucial factors in antimicrobial activity. Given the brief periods during in which the elevators were unoccupied in this study, the exposure time in the case of the “Motion-sensor” mode elevator may have been insufficient, particularly considering the specific time requirements to achieve significant microbial log reductions.

Environmental factors such as temperature, humidity, and air circulation within the elevators may also have influenced the efficacy of UV lamps. These environmental variables may have contributed to the similar microbial loads observed in both elevators investigated in the study.

The regular human traffic in university elevators may have led to continuous microbial reintroduction, potentially offsetting the effects of UV disinfection. This is particularly relevant in high-traffic settings like university campuses.

Airflow is another factor which may have had an impact on the observations in this study. In the future, a study to monitor the ability of elevators to push large volumes of air around a building from floor-to-floor and to explore its implications for infection transmission would be relevant.

The observations in this study emphasise the need for a holistic approach to UV disinfection that considers optimal lamp placement, adequate exposure duration, and ambient environmental conditions. The integration of UV disinfection with other hygiene practices is crucial, especially in areas with high footfall.

The main limitation of the study was the relatively low sample size. The sample size in this study was only sufficient to state that UV-222 lamps had no strong effect on the microbial load, found on air and surfaces. It is possible that some of the some of the differences – although small – would have been significant with a larger sample size. Based on this study, whether there was little or no effect, cannot be differentiated.

As Hessling et al. summarised in their review, UV-222 in a dose of 100 mJ/cm2 should reduce most pathogens by several orders of magnitude without harming human skin or eyes [1]. The UV lamp used in this study emitted light with a radiance of 2,146 μW/cm2 from a one-meter distance, and 0,536 μW/cm2 from two meter (Figure 2B). The dose (mJ/cm2) can be calculated as intensity (mW/cm2) x time (seconds) [3]. It means that our lamp needs 13 hours or 52 hours to reach the above-mentioned 100 mJ/cm2 intensity, respectively. If that is the case, it is possible that the elevator re-contaminating fast enough by continuously changing people to cover the effect of the UV lamp. The number of people present in the elevator immediately before sample collection was a factor that could not be controlled in this study. It may have had a significant impact on the microbial load and potentially may have masked the effects of UV-light.

The systematic review by Hessling et al. [1] also summarised log reduction values and the appropriate irradiance found in studies and presented these results in a table where the median value for the log-reduction dose was determined for each microorganism. Most studies used liquid samples, and part of them used different wavelengths, but those conditions are not relevant for this study. Table V is adapted from the table presented in the systematic review [1]. It shows the rows of the original table where the 222 nm wavelength was applied, and surface samples were investigated. Viruses were excluded, as in our study we did not detect viruses. Table V also indicates (based on the log-reduction data) the time that our UV lamps need to reach the light energy value that corresponds to log1 reduction if the lamp is 1- or 2-meters away from the investigated surface, which was the typical distance in our study between the sampling sites and the lamp.Table V Light energy needed to reach log101 reduction in the case of different species, using 222 nm wavelength and surface samples, published by Hessling et al., in 2021 [1], and the calculated time our lamp needed to reach these light energy values if applied from 1- or 2-meters distance

Table VSpecies	Median log-reduction dose (mJ/cm2)	Time required for our UV-lamps to reach log101 reduction (minutes)	
1-meter distance	2-meters distance	
Bacillus subtilis spores	0.89	7	28	
Staphylococcus aureus	1.46	11	45	
Bacillus megatherium phage	4.79	37	149	
Enterococcus faecalis	7.59	59	236	
Bacillus pumilus spores	8.52	66	265	
Saccharomyces cerevisiae	12.77	99	397	
Streptomyces griseus spores	14.38	112	447	
Acinetobacter radioresistens	16.43	128	511	
Clostridioides difficile spores	16.67	129	518	
Escherichia coli	63.56	494	1976	
Salmonella typhimurium	109.32	849	3399	
Listeria monocytogenes	145.65	1131	4529	

There is no clear recommendation on what is the required log reduction value we should reach with the UV decontamination in an elevator. As a comparison, it is of note that log102 – log104 reduction can be reached by hand rubbing with alcohol.

A recent study evaluated the of far-UV radiation as an alternative to hand rubbing for hand hygiene [11]. While the study found far-UV light to be effective in reducing CFU on hand samples, this reduction was lower than alcohol-based handrubs could result. Specifically, irradiation with 23 mJ/cm2 of UV-222 on hand resulted 1.04 ± 0.13 log10 reduction, whereas alcohol-based hand rubs achieved a reduction 1.89 ± 0.10 log10 reduction. The study also reported that the reduction effect of UV-222 on hands was significantly lower than that previously reported for suspensions.

Conclusions

While this study did not demonstrate a significant impact of UV lamps on reducing microbial loads in the elevators which were investigated, the study findings demonstrated the complexities and nuances of applying UV disinfection in real-life settings.

Subsequent studies should focus on varying the placement and quantity of UV lamps, extending exposure times, and identifying the types of microorganisms present. This approach would provide a more comprehensive understanding of UV disinfection efficacy in real-world scenarios, thereby enhancing public health safety measures as well as being relevant for healthcare settings.

Funding

The UV lamps were kindly offered for the study by UVMedico, and they also carried out the installation.

Conflict of interest statement

The authors declare no conflict of interest.

Ethics

Not required for this study.

Informed consent

Not required for this study.

Appendix A Supplementary data

The following is the Supplementary data to this article:Multimedia component 1

Multimedia component 1

Acknowledgement

The study was funded by the HEALTHY SAILING project (grant number 101069764), part of the Horizon Europe HORIZON-CL5-2021-D6-01 initiative, supported by the European Union.

Appendix A Supplementary data to this article can be found online at https://doi.org/10.1016/j.infpip.2024.100390.
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References

1 Hessling M. Haag R. Sieber N. Vatter P. The impact of far-UVC radiation (200-230 nm) on pathogens, cells, skin, and eyes - a collection and analysis of a hundred years of data GMS Hyg Infect Control 16 2021 16 Doc07 10.3205/dgkh000378 eCollection 2021
2 Mohania D. Chandel S. Kumar P. Verma V. Digvijay K. Tripathi D. Ultraviolet Radiations: Skin Defense-Damage Mechanism Adv Exp Med Biol 996 2017 71 87 10.1007/978-3-319-56017-5_7 29124692
3 Reed N.G. The history of ultraviolet germicidal irradiation for air disinfection Publ Health Rep 125 2010 15 27 10.1177/003335491012500105
4 Eadie E. Hiwar W. Fletcher L. Tidswell E. O'Mahoney P. Buonanno M. Far-UVC (222 nm) efficiently inactivates an airborne pathogen in a room-sized chamber Sci Rep 12 2022 4373 10.1038/s41598-022-08462-z 35322064
5 Coohill T.P. Virus-cell interactions as probes for vacuum-ultraviolet radiation damage and repair Photochem Photobiol 44 1986 359 363 10.1111/j.1751-1097.1986.tb04676.x 3786457
6 Kandel C.E. Simor A.E. Redelmeier D.A. Elevator buttons as unrecognized sources of bacterial colonization in hospitals Open Med 8 3 2014 e81 e86 eCollection 2014 25426176
7 Pereira da Fonseca T.A. Pessôa R. Felix A.C. Sanabani S.S. Diversity of Bacterial Communities on Four Frequently Used Surfaces in a Large Brazilian Teaching Hospital Int J Environ Res Publ Health 13 2016 152 10.3390/ijerph13020152
8 Hygiena, UltraSnap Instructions. https://www.hygiena.com/documents/64066/ultrasnap-instructions-en.pdf, (accessed 23 August 2024).
9 Xu L. Zhang C. Xu P. Wang X.C. Mechanisms of ultraviolet disinfection and chlorination of Escherichia coli: Culturability, membrane permeability, metabolism, and genetic damage J Environ Sci (China) 65 2018 356 366 10.1016/j.jes.2017.07.006 29548407
10 Yang C. Sun W. Ao X. Bacterial inactivation, DNA damage, and faster ATP degradation induced by ultraviolet disinfection Front Environ Sci Eng 14 2020 13 10.1007/s11783-019-1192-6
11 Hessling M. Sicks B. Lau B. Far-UVC Radiation for Disinfecting Hands or Gloves? Pathogens 12 2023 213 36839485
