Ultraviolet-C radiation: A supplemental tool for disinfection

: In response to the COVID-19 pandemic, healthcare facilities have pur-chased more ultraviolet-C (UVC) disinfection devices than in previous years. This article discusses the safety and efficacy of UVC disinfection in healthcare settings.


DESIGNPRAX/SHUTTERSTOCK
The COVID-19 pandemic brought changes to healthcare and infection prevention practices around the world. Efforts to limit transmission of the virus have included increasing the use of personal protective equipment, increasing the frequency of cleaning and disinfection, and expanding the use of air filtration and purification systems. UV disinfection devices are one example of a technology that has rapidly grown in popularity during this time.
Healthcare facilities have greatly expanded their use of UVC disinfection devices for regular disinfection of patient rooms, on-demand disinfection of workstations, purification of air, and decontamination of N95 masks. ECRI, an independent wavelengths (320-400 nm), followed by UVB (280-320 nm), and UVC radiation, which has the shortest wavelengths (200-280 nm). While all three types of UV radiation are emitted by the sun, only UVA and UVB radiation reach Earth; all UVC and some UVB radiation are absorbed by the ozone layer.
Radiation in the UVC range, and to a lesser degree in the UVB range, can disrupt the DNA and RNA structures in bacteria, viruses, and fungi. 6 This inactivates the microorganism, prohibiting it from replicating and infecting a host. Radiation between 260 nm and 265 nm aligns with the peak absorption range of bacterial DNA and is therefore very effective at breaking the bonds in that DNA. 6 There is also evidence that very highintensity UV radiation can overheat cells, causing them to rupture. 7 The ability of UVC light to inactivate pathogens without leaving any chemical residue makes it an attractive option for healthcare applications. Sources of UVC light for healthcare facility use include: • Low-pressure mercury lamps, which emit radiation at 254 nm (close enough to the peak absorption of DNA to maintain high effectiveness). These lamps are the most common source of UVC light. They have been manufactured for decades and their germicidal effectiveness is well-supported by peerreviewed studies. 4 • Pulsed xenon lamps, which emit light at multiple peaks across the UVB and UVC spectra. These lamps emit high-intensity bursts of light over a fraction of a second. 8 • Ultraviolet light-emitting diodes (LEDs), which commonly emit light in the 260-280 nm range. LEDs allow the wavelength to be closely controlled, but the intensity of the emitted light tends to be lower than in other common sources. As a result, LEDs are more common in small-scale applications, like those for disinfecting computer keyboards. 9 • Far UVC excimer lamps, including krypton-chloride (KrCl) lamps, which emit light at a peak of about 222 nm. These lamps have gained interest due to new research suggesting that exposure to Far UVC radiation (200-230 nm) may be safe for mammalian skin and eyes. In fact, experts at the International Ultraviolet Association have recognized that the technology has great potential; however, they continue to advise caution in occupied spaces, emphasizing that room occupants should not exceed the American Conference of Governmental Industrial Hygienists (ACGIH) exposure limits for any wavelengths emitted. 10 The ACGIH has recently adopted changes that raise acceptable limits for wavelengths below 250nm, reflecting this new research. 11 UVC light has been used in other industries and for other disinfection applications for many years. For instance, it has been used in water disinfection for more than a century, with the first application reported in France in 1910. 12 Later, UVC light was used to disinfect air to combat measles and tuberculosis outbreaks. 12 Unfortunately, UVC light has not demonstrated consistent, highquality evidence of reductions in infection rates. Some studies have organization that performs handson medical device evaluations and custom cost analyses to help healthcare facilities make informed purchasing decisions-saw more than twice as much interest in UVC room disinfection devices in 2020 as compared with 2019. 1 UVC disinfection devices have also become increasingly used in public spaces like mass transportation and schools. 2,3 ECRI reports that, when used correctly, UVC disinfection technologies can be a useful supplement to manual cleaning and disinfection efforts to combat environmental bioburden. 4 A direct link to reduced infection rates, however, has not been clearly established. In addition, users must exercise caution, as exposure to high doses of UVC radiation (also called UVC light) may be unsafe, presenting a risk of painful inflammation of eye tissue. 5 This article examines whether UVC radiation is safe and effective in healthcare settings.

Types of UV radiation
The term UV radiation refers to a subset of electromagnetic (EM) energy that is invisible to the human eye. UV radiation is divided into three primary bands: UVA, UVB, and UVC (see Visible light spectrum). In this region of the EM spectrum, wavelengths are measured in nanometers (nm), where 1 nm equals one-millionth of a millimeter. UVA radiation has the longest

Visible light spectrum
The ultraviolet and visible light portions of the electromagnetic spectrum. UVC light falls between 200 and 280 nm.
been able to demonstrate reductions in healthcare-associated infections (HAIs) or other infection rates, whereas some systematic reviews have concluded that the evidence is mixed or weak. 13 One prominent example, Clostridioides difficile (C. Diff) is relatively difficult to inactivate in its spore form. Starting around 15 years ago, many studies have correlated the dose of UVC light with a log reduction of C. Diff spores. Although the studies showed great variation depending on test conditions and strains of C. Diff, many have demonstrated up to 3-or 4-log reduction (99.9%-99.99% reduction, respectively) in spores after exposure to UVC light. [19][20][21][22][23] This can greatly reduce the potential of surfaces in the healthcare environment to serve as a transmission pathway to patients and staff.

UVC disinfection in clinical workflow
UVC disinfection technologies are available in a range of products and styles, from room and air disinfection systems to handheld wands and countertop disinfection boxes (see Common UV disinfection technologies).
Since 2010, ECRI has observed that healthcare settings are more interested in portable UVC room disinfection devices than other UVC devices.
When initiating a UVC room disinfection program, infection preventionists and environmental services (EVS) managers develop plans for implementing the technology effectively. They consider which rooms have the highest need (isolation rooms, ORs), how frequently these rooms should be targeted (daily, at patient discharge), and how to fit the use of UVC disinfection into the existing EVS workflow. The devices are typically operated by EVS staff. Sometimes, program coordinators will select a dedicated user to run disinfection cycles by bringing the UVC device from room to room. Other times, EVS staff will add the use of UVC disinfection devices into their normal terminal cleaning and disinfecting procedures.
These procedures begin with manual cleaning and disinfection of soiled surfaces throughout the room and adjoining bathrooms. The staff member then sets up the UVC emitter, most commonly near the middle of the room, exposes shadowed surfaces, leaves the room, and finally runs a UVC cycle as directed by the manufacturer. They may also run a separate cycle in the bathroom. As soon as the UVC disinfection cycle ends, staff may enter the room to remove the UVC device and prepare for the next patient. The total UVC cycle typically takes between 15 and 40 minutes. Because the room must be unoccupied during this time, UV disinfection can greatly increase room turnover time and may not be a practical solution for rooms or departments that require rapid turnover.

Safe and effective use
UVC disinfection is intended to supplement, not replace, existing infection prevention measures. Whereas manual cleaning and disinfection are only effective on the specific surfaces where staff members actively wipe and maintain the recommended wet time, UVC disinfection can provide broad coverage with little input required by the operator. However, it is not sufficient to place the UVC device haphazardly in a room. To be effective, UVC devices must deliver an adequate dose of UVC energy to each target surface. The required dose depends on the target organism and environmental conditions, such as a humid or dry environment. 24 The UVC dose is equal to the intensity of the UVC light multiplied by the duration of exposure. Intensity is in turn governed by the inverse square law, which states that intensity is proportional to the inverse of the square of the distance from the source: doubling the distance from the UVC source will reduce the intensity to 25%. Therefore, surfaces that are closer to the UVC source will receive a higher dose throughout a disinfection cycle.
Device operators should also consider the effect of shadowing. Objects between the UVC source and the target organism can create a shadowing effect, hiding the organism from UVC light. Large objects like beds and chairs and small particles or irregularities in the surface of objects like soil, puddles, biofilms, and even other organisms can shield a target organism. Even clear plastics and glass can absorb UVC light and shield items and organisms from exposure. 25 Infection prevention effectiveness is also a function of the frequency of disinfection. After intermittent disinfection, microorganisms are eventually reintroduced to a surface or a space, and their number tends to continue to grow. If disinfection is performed at shorter intervals, the microorganisms have less time to be reintroduced or to proliferate, and the background level of contamination will tend to be lower.
One of the major challenges that interfere with frequent or constant UVC disinfection is that UVC light is generally not safe for human exposure, so cycles must be performed only when a room is unoccupied. The major risks of exposure are erythema and photokeratitis. 5 Several organizations have published guidelines for maximum acceptable exposure levels. The maximum recommended exposure for a 254 nm wavelength is 6 millijoules per square centimeter (mJ/cm 2 ) per 8-hour shift. 5 Depending on the UV device and its position within a room, this exposure level can be exceeded within seconds of entering a room.
Most UVC room disinfection devices have motion sensors that automatically shut off the lamps if motion is detected, but it' s best not to rely on these features. If you need to enter a room and signs are posted to indicate that a UVC disinfection cycle is in progress, wait until the cycle has finished. If you cannot wait, find the EVS staff member assigned to the device and ask them to remotely terminate the cycle.
Another key consideration is the potential for material degradation after exposure to UVC light. Some materials, such as plastics and rubbers, are sensitive to UVC light and may develop discoloration or crazing after prolonged exposure. Because UVC light does not penetrate far into materials, degradation is superficial; unless a material is very thin, it is unlikely to be noticeably weakened. Nevertheless, UVC degradation may have aesthetic or functional impacts, such as by causing haze on some device displays. Degradation is proportional to the cumulative dose of UVC light over the lifetime of an object. By keeping devices at a reasonable distance away from high-intensity UVC sources, the devices can receive adequate but not excessive disinfection doses. In some cases, it may be appropriate to cover very expensive or sensitive pieces of equipment with a drape before a UVC disinfection cycle. 25

The future
The COVID-19 pandemic has created a growing market for the purchase of UVC disinfection devices. For one, UVC devices have entered the consumer market at a much larger scale than in the past. Some popular applications include handheld wands; mask disinfection devices; devices for disinfecting small objects such as phones, keys, and baby UVC disinfection is intended to supplement, not replace, existing infection prevention measures.
bottles; and small room disinfection devices. These devices are not strictly regulated, though the US Environmental Protection Agency has the authority to take action against manufacturers that make false claims about their products. In healthcare, ECRI has seen increasing interest in previously minor categories of UVC disinfection, such as upper-air UVC devices (which are located in the upper portion of a room, above the occupied space, to disinfect air as it circulates) and Far-UVC lights. There has also been a tendency to blur the lines between healthcare and consumer devices, such as nurses who purchase their own devices and use them to disinfect their workspaces. This may be a temporary change resulting from limited healthcare-grade device availability and increased disinfection vigilance in the early phases of the pandemic.
Some of these trends may continue, but others may prove to be too expensive to maintain indefinitely. All categories of UVC disinfection require some additional labor in the form of installation, device maintenance, or increased cleaning and disinfection time.

Conclusion
UVC disinfection has the potential to supplement manual cleaning and disinfection practices. These devices can inactivate microorganisms when surfaces are cleaned of soil and targeted with an adequate UVC dose, inactivate pathogens in the air, and may help reduce the likelihood of disease transmission. However, UVC is far from a guaranteed solution. Studies have not consistently and directly demonstrated reductions in HAI rates or COVID-19 transmission rates. Facilities and device operators must take care to implement these technologies safely. Mobile UVC disinfection devices should not be used in occupied rooms and healthcare workers should take care not to enter a room when a disinfection cycle is in progress. Permanently installed UVC disinfection technologies should not expose any room occupants to UVC in excess of recommended exposure limits. ■