Microbiological and epidemiological evidence shows that contaminated surfaces can contribute to the transmission of infectious disease-causing germs and allergens. Hospital studies show that staff and new patients have been infected if a prior room occupant had methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant enterococci (VRE), Clostridium difficile, Acinetobacter baumannii, and other pathogens.

Naturally, an effective way to overcome or minimize the spread of disease is to inactivate and reduce the number of germs in the environment. Improved surface cleaning and disinfection are key methods, but studies provide critical information on improving air quality and decreasing risk on surfaces that people touch such as in hospitals and care homes as well as hotels, restaurants, airports, convention centres, schools, and public washrooms.

Manual processes for cleaning and disinfection are frequently sub-optimal, suggesting that automated disinfection processes might offer an opportunity to improve cleaning efficacy and consistency.

Light that is visible to humans is part of the light spectrum from 380 to 740 nanometres. Ultraviolet-C (UVC) light, between about 200 and 280 nm, is known to be harmful to microorganisms and can be used as a disinfection method. Using UVC light against microorganisms is not a new idea, but the COVID-19 pandemic increased the development and deployment of UVC light and violet-blue light disinfection technologies that are available and used as commercial systems.

ISSA receives many questions about the use of these lamps for disinfection; education and training should be provided on any technologies to incorporate them into existing cleaning processes. The Global Biorisk Advisory Council (GBAC) team provides guidance on the adoption and implementation of technologies by ensuring that efficacy, as well as logistical and safety issues, are established in real-world indoor spaces.

Are UVC light disinfection systems currently in use?

UVC radiation is a known disinfectant for air, water, and nonporous surfaces. UVC radiation has effectively been used for decades to reduce the spread of bacteria, such as tuberculosis, and has been shown to destroy the outer protein coating of bacteria and viruses. This destruction ultimately leads to inactivation of the microorganism. For this reason, UVC lamps are often called “germicidal” lamps.

In addition to understanding whether UVC light is effective as a disinfectant, its efficacy is dependent upon the organic load and microorganisms, the intensity and time of exposure, the distance from the surface, and whether the surface is within direct line of sight.

• Direct exposure: UVC light can only inactivate a germ if the germ is directly exposed to the light. Therefore, the inactivation of bacteria and viruses on surfaces may not be effective due to blocking of the UV radiation by soil, shadow, or obstruction by other contaminants such as body fluids.
• Dose and duration: UVC light requires sufficient duration of exposure to be effective and this can vary for different microorganisms.

What are the different types of lamps for UV light disinfection systems?

Not all UVC lamps are the same. Lamps may emit specific wavelengths or a broad range, and some also emit visible and infrared radiation. The wavelengths emitted by the lamp may affect the lamp’s effectiveness at inactivating microorganisms and may impact the health and safety risks associated with the lamp.

UV light disinfection systems both commercially available and being researched include:

1. Ultraviolet-C (UVC) light (254 nm), the most common type of lamp used, is a low-pressure mercury lamp that continuously delivers wavelengths of UV light with a peak emission around 254 nm.
2. Pulsed-xenon ultraviolet (PX-UV) light (200-1100 nm) systems use xenon gas bulbs that emit a broader spectrum of light (including UV, visible, and infrared) in short pulses ranging from 200 to 1100 nm. This range covers the germicidal spectrum of 200 to 280 nm.
3. Far-UVC light (222 nm), such as Krypton Chloride (KrCl) excimer lamps, has been shown to inactivate bacteria and viruses and are much less likely to induce adverse reactions on skin and eyes and have the potential to be safer for humans.
4. High-Intensity Narrow Spectrum (HINS) light (380 to 420 nm) devices use LEDs that emit a very narrow wavelength of visible violet-blue light with at least one peak wavelength of 380 to 420 nm. This narrow bandwidth with peak output usually of 405 nm induces inactivation of a range of bacterial pathogens.

What are the safety considerations?

UVC for surface and air decontamination must consider health and safety issues as well as the risk of incomplete inactivation of bacteria and viruses. Risk depends on the UVC wavelength, dose, and duration of exposure. The risk may increase if the unit is used by untrained individuals.

• Direct exposure of skin and eyes to UVC radiation from some UVC lamps may cause painful eye injury and burn-like skin reactions. Never look directly at a UVC lamp source, even briefly. There are no immediate warning symptoms to indicate overexposure to UVC radiation.
• Some UVC lamps generate ozone, which can be irritating to the airway when inhaled.
• UVC can degrade certain materials, such as plastic, polymers, and dyed textile.
• Some UVC lamps contain mercury. Because mercury is toxic even in small amounts, extreme caution is needed in cleaning a lamp that has broken and in disposing of the lamp.

Personnel must not enter a room while the UV light system is operating. If there is a risk of exposure, the appropriate PPE must be worn that protects the eyes and skin and includes gloves, clothing with no skin showing, and a UV-resistant face shield.

There is no Occupational Safety and Health Administration (OSHA) standard from the U.S. Department of Labor regarding exposure to UVC light, but the OSHA general duty clause states the employer must provide a workplace free of recognized hazards that may cause death or serious physical harm.

Are there any practical or logistical considerations?

There are multiple variables that affect the amount of UVC delivered to surfaces and the resulting reduction of infectious agent achieved; these include the amount of irradiance generated by the UVC device, the distance from the device to the exposed surface, the angle at which the UVC strikes the surface, and whether the surface is in direct line of sight of the device or receives light that has been reflected off other objects (i.e. surfaces in shaded areas). These factors must be taken into consideration when assessing the potential effectiveness of a UVC device.

• Use of UVC light systems for surface disinfection should only be undertaken following completion of a manual clean as residual dirt can reduce efficacy.
• Prior to a UVC light system being considered, an assessment of the area to be disinfected must be undertaken to ensure the area can be sealed and the use of UVC light made safe.
• Manufacturers’ instructions for use must be followed to ensure all surfaces are adequately disinfected to reduce the risk of sub-optimal UV light dosage on microorganisms. This could result in mutation of the remaining microbes.
• UV light systems in use must be maintained in good working order and a system of programmed maintenance in place with documented evidence.
• A quality assurance mechanism should be in place to monitor the functionality of the UV light system using samples before and after cleaning.
• Risk assessments should be in place for possible exposure of people and animals to UVC light.
• Ensure appropriate time is given to the UVC light disinfection process.

To learn more about UV light disinfection devices, you should:

• Ask for education and training opportunities.
• Ask the manufacturer about the device’s health and safety risks.
• Ensure you understand the instructions for installation, use, cleaning, and maintenance.
• Test the lamp to determine whether the lamp emits other wavelengths and if so, how much.
• Ask what kind of material is compatible with UVC disinfection.
• Ask whether the device generates ozone.
• Ask whether the lamp contains mercury.

Studies have concluded that using a UVC light system in combination with standard cleaning was more effective at reducing infectious disease-causing germs and decreasing risk of infection than standard cleaning alone. But many of these studies do not define the standard cleaning performed. Recommendations have included that UVC light systems should be utilized by dedicated cleaning personnel who have been educated and trained on their use. It is important to consider that creating a safe and healthy indoor space requires a combination of multiple interventions.

Dr. Gavin Macgregor-Skinner is a senior director of the Global Biorisk Advisory Council™ (GBAC), a division of ISSA. As an infection prevention expert and epidemiologist, he works to develop protocols and education for the global cleaning industry.