Hospital-acquired infections (HAIs) continue to be a significant problem in healthcare facilities throughout the world. A 2014 CDC study estimated that at any given time, one out of every 25 patients in acute care in the U.S. was afflicted with an HAI, and the World Health Organization (WHO) estimates that seven out of every 100 patients hospitalized in a developed country will acquire at least one HAI.
A 2007 CDC study estimated approximately 1.7 million annual HAIs in the U.S. alone, resulting in approximately 99,000 associated death. There is a significant economic cost associated with treating these infections, with estimates reaching as high as $45 billion annually in the U.S.
The Current Approach
Environmental contamination has an established role in the transmission of infections, so patient exposure to clean spaces and surfaces is an important part of curbing HAI acquisition. Traditional cleaning practices, however, may not be sufficient to remove pathogens from surfaces in a healthcare setting.
A 2006 study showed that in an evaluation over three different hospitals, up to 55 percent of high-touch objects in a patient room were not cleaned during typical terminal cleaning. A 2009 study showed that in one hospital, 24 percent of studied high-touch surfaces tested positive for methicillin-resistant Staphylococcus aureus (MRSA), even after being cleaned. Results such as these highlight the need for additional methods of environmental disinfection.
One technology that has seen increased use as a supplement to traditional cleaning methods is the use of far-ultraviolet (UVC) light-emitting devices. The UVC photon, typically generated in these devices by a mercury lamp with a peak emission at 254 nanometers (nm), damages the DNA of exposed bacteria, resulting in the death of the bacterial cell. However, this light can be extremely hazardous to humans, and thus the area being cleaned must be completely unoccupied during the use of these devices.
Because the cleaning process may take anywhere from a few minutes to a few hours, the room being treated is unavailable for use during that period. These systems are also therefore not able to be used in a room that is occupied continuously by a patient, and thus would typically only be useful during terminal cleaning. Furthermore, these devices require specialized training and knowledge to be operated correctly and safely.
The Potential Solution
An alternative technology showing promise for supplemental disinfection is the use of near-ultraviolet (UVA) light. UVA light, applied at the correct intensity and duration, can kill pathogens while remaining safe for human exposure, allowing it to be used in occupied spaces.
This lighting can be incorporated into standard light fixtures and controlled automatically, enabling its use without any action from hospital staff. There are two primary requirements that must be considered for this solution to ensure its effectiveness and suitability for application: it must be safe for people in the space in which it is used, and it must effectively reduce the quantity of pathogens in the space.
Photobiological Safety of a UVA Disinfection System
To assess the hazards posed to humans by the optical radiation of a lighting system, the International Electrotechnical Commission (IEC) and the International Commission on Illumination (CIE) established guidelines in IEC standard 62471. This standard defines hazard levels for actinic UV (primarily far- and mid-UV, or UVC and UVB), near UV (UVA), blue light, and infrared radiation.
At sufficient intensities, near UV radiation has the potential for damage to the eye, and actinic UV radiation has the potential for damage to both skin and eye. Blue light poses the risk of photochemical injury to the retina. The spectral weighting functions for the assessment of actinic, UVA, and blue light hazards as defined by this standard are shown in Figure 1.
Because the emission of a UVA disinfection lighting system is in the ranges covered by the spectral weighting functions for actinic UV (200 nm to 400 nm) and near UV (315 nm to 400 nm), these hazards are of primary interest for a more detailed evaluation. IEC 62471 prescribes that lamps or lighting systems that do not meet defined hazard thresholds are considered to not pose any photobiological hazard to humans for exposures up to the maximum defined exposure duration of eight hours. This limit is 10W per square meter (W/m²) for near UV radiation, and 0.001 W/m² for actinic UV.
Consider an exemplary UVA disinfection lighting system consisting of UVA-emitting luminaires recessed into a hospital ceiling at a height of 300 cm. These luminaires emit disinfecting light with a peak wavelength of approximately 368 nm and a full width at half-maximum of approximately 9 nm. The intensity of UVA irradiation would necessarily be more intense close to the luminaire (far from the floor), and less intense further away (close to the floor). For this exemplary system, the UVA irradiance is shown as a function of distance from the floor in Figure 2.
There are two irradiance levels and their corresponding distances that are noteworthy. Firstly, the irradiance reaches 10 W/m² at approximately 210 cm above the floor. This is important because 10 W/m² is the limit below which the system can be considered to pose no photobiological hazard for exposures up to eight hours. This means that the disinfection lighting system can be energized for up to 8 hours per day, while posing no risk to people in the room (as the head of even a very tall person would not protrude 210 cm or more above the floor).
The second key intensity to note is that the irradiation at a height of 100 cm is approximately 3 W/m². 100 cm is the height above the floor at which many high-touch objects may be found, such as bed rails, countertops, and sinks. Because these high-touch objects and surfaces can play a role in infection transmission, it is important that this level of irradiance provide significant pathogen reduction.
Germicidal Efficacy of a UVA Disinfection System
To potentially reduce the rate of HAIs it is critical that a technology effectively reduce the quantity of pathogens on the treated surfaces or objects. A study, presented as a poster at the 2018 Society for Healthcare Epidemiology of America (SHEA) Spring Conference, examined the effect of such a system on a variety of pathogens related to hospital acquired infections.
The study, which exposed pathogens on steel disks to the UVA disinfection light, found that an eight-hour exposure at an intensity of 3 W/m² reduced MRSA, E. coli, and bacteriophage MS2 by greater than 1 log10 (i.e. over a 90 percent reduction). S. aureus and E. coli species are both causes of HAIs, with a 2014 study ranking them as the second and fourth most frequently reported causative pathogens, respectively. While bacteriophage MS2 is non-pathogenic to humans, it is often used as a surrogate for norovirus, which one 2012 survey of U.S. hospitals found to be the cause of 18 percent of investigated outbreaks.
Improved environmental disinfection has the potential to reduce the number of contracted HAIs, and a UVA disinfection lighting system may be an effective supplement to existing cleaning methods. The financial benefits of improved HAI prevention may range from $6 billion to as high as $31.5 billion annually in the U.S., if between 20 and 70 percent of HAIs are assumed to be preventable.
There may be additional needs to reduce environmental pathogens to prevent community acquired diseases. Some examples might be the need to reduce MRSA in locker rooms or in other public spaces, as community-acquired MRSA becomes a growing threat to consider alongside hospital-acquired diseases.
There exist also potential applications in spaces outside of the healthcare or community settings. The CDC estimates that there are 48 million foodborne illnesses every year, resulting in 128,000 hospitalizations and 3,000 deaths. Since typical cleaning procedures used in the food industry may not remove all bacteria from cleaned surfaces, UVA disinfection may be a useful supplement in the food and beverage industry as well.
About the author
Kevin Benner is a Lead Design Engineer in the New Technology Introduction group at Current, Powered by GE, where he works on the development of innovative lighting technologies including safe disinfection lighting. He has a background in mechanical engineering and color science and is a graduate of The Ohio State University.