The germicidal properties of ultraviolet light are of renewed interest to clinicians wanting to employ technology in the fight against healthcare-acquired infections (HAIs). Essentially, ultraviolet light kills bacteria and viruses by damaging their nucleic acid, thus destroying their ability to replicate and cause disease. UV wavelengths, which range from 1 to 400nm, are beyond the range of visible light, and UV rays with wavelengths shorter than 300nm can kill pathogenic microorganisms. Most experts agree that the C bandwidth is the most germicidal, and that UVC light can remove approximately 99 percent of microbial contamination in the air and on surfaces. The energy required to kill microorganisms is a product of the UV light’s intensity and exposure time, measured in micro-watt seconds per square centimeter. For example, to achieve a 99 percent kill rate, the following exposures are necessary:
• Aspergillus flavus: 60,000 mW S/cm2
• Rotavirus: 21,000 mW S/cm2
• Hepatitis virus: 8,000 mW S/cm2
• Salmonella enteritidis: 7,600 mW S/cm2
• E. coli: 7,000 mW S/cm2
• Influenza virus: 6,600 mW S/cm2
• Shigella dysenterie: 4,200 mW S/cm2
• Legionella pneumophila: 3,800 mW S/cm2
UVC light lends itself to numerous applications in the healthcare environment. It can be employed via fixtures for coil irradiation in HVAC systems; UVC air cleaners can be used for air-stream irradiation; fixed, portable and handheld UVC-emitting devices can be used for surface sterilization; and a combination of UVC air and surface sterilization devices can be used in operating rooms and other high-risk areas in the hospital. Air and surface sterilization using UVC light is differentiated by the amount of time during which microorganisms are exposed to UVC radiation. Surface contamination is fixed in nature, so less UVC intensity is required; however, because pathogens move much more swiftly in air streams, a much greater concentration of UVC light is required for microbial kill. Efficacious sterilization by UVC light is determined by light intensity, duration of exposure, and distance of the UVC light from the surface or the air stream.
There are a number of devices in the marketplace currently that harness and use UVC light as a weapon of pathogen destruction. Steril-Aire Inc. offers a full line of UVC Emitters™ that are used in hospitals worldwide for infection and indoor air quality control. Lumalier Corporation’s In-Duct UVGI air disinfection is designed to reduce viral and bacterial contaminate of passing air in HVAC systems to a 3-log level of disinfection. Bioscide’s TRU-D rapid room sterilization system uses a real-time calibration system to adjust the dosage time to the dynamics of a room. Germgard Lighting LLC offers a shoebox-sized sanitation device for the gloved hand, based on the company’s proprietary UV-C light technology that removes pathogens after 3 seconds of exposure.
For all of the information about UVC technology currently in the marketplace, many healthcare providers may not be cognizant of the benefits and germicidal properties of UV lighting.
“I think the most common misperception is that all UV lights are more or less the same in their ability to kill infectious organisms,” says Robert Scheir, PhD, president and chairman of Steril-Aire, Inc. “In fact, UV devices on the market today vary widely in germicidal output, especially when installed in colder-air environments such as HVAC systems. The Environmental Protection Agency (EPA), through its Homeland Security Department, has commissioned studies comparing the performance of leading UV devices in inactivating bacterial and viral organisms. These reports provide a useful benchmark for comparison.”
“There is considerable evidence reported in the literature to demonstrate the value of a pathogen-free environment,” says Mark Stratham of Bioscide. “Air sterilization is one component of an overall strategy to eliminate transmission of pathogens. The use of germicidal ultraviolet technology is a cost-efficient way to eliminate viral and bacterial particles that may be transferred throughout a facility. It is especially cost-effective for retrofits when a non-proprietary UV-C generating system is used.”
Chuck Dunn, president of Lumalier Corporation, says that clean environments in healthcare facilities are usually taken for granted. “My facilities manager tells the infection control/safety committees he’s changing filters and the interior of the air handling units are spotless, though it is unlikely an ICP ever makes a visual inspection of the mechanical equipment,” Dunn says. “Over the past decade, unscrupulous UV vendors have sold hospitals poor-performing UV equipment, unreliable lamps that last only months and are proprietary to the UV vendor and very expensive to replace, as only the UV manufactures lamps fit the UV equipment. This has left the impression with many users that UV systems for HVAC equipment are generally problematic and expensive to maintain.”
Dunn points to the importance of understanding how at-risk settings like hospitals can benefit from upper-air UV systems that can address lingering airborne pathogens: “Though most all of the scientific data in regard to TB control states that all airborne viral or bacterial contaminate transmitted in the form of airborne droplet nuclei is susceptible to UV, a common misconception is that ‘If I don’t have ongoing TB conversions I don’t have a problem with airborne contaminate.’ The fact that without proper and ongoing air disinfection that airborne contaminate settles to surfaces and recontaminates clean surfaces in short order is not getting through to healthcare workers. A study by Stephanie J. Dancer in the February 2008 issue of The Lancet states, “Other studies have specifically looked for MRSA in the air in hospitals. One such study did sequential air sampling before and after bed-making and showed that MRSA counts remained elevated for up to 15 minutes after the bed was made.”
There seems to be no lack of scientific evidence supporting the germicidal properties of UVC light. “UV germicidal irradiation (UVGI) has been used worldwide for nearly a century to kill microorganisms in air and water, and the scientific literature abounds with data on this topic,” Scheir notes.
Stratham emphasizes that UVC light is a no-brainer: “My background is in microbiology, so when someone asks me if UVC is capable of disinfection, it sounds the same to me as if one were to ask, ‘Is bleach a disinfectant?’ For both questions, the answer is the same. There is a body of evidence that has evolved over the last 50 to 60 years demonstrating the efficacy of both strategies. As with all disinfectant, dosage is critical. If you were to ask for a recent authoritative study, one could look to the EPA’s recent work; however, I believe it is more a matter of common sense. Remove pathogens from the air, reduce the risk of infection. It should not require extensive studies to tell us this. Deciding on the best strategy to achieve this goal will depend on the particular situation and budget restraints.”
There is no limit to the applications for UVC light in hospitals. Peter Gordon of Germgard Lighting LLC emphasizes that UVC light should be used for the instant sanitation of the contaminated gloved hands of healthcare workers.
Scheir says that hospitals are moving away from UV lights used for upper-air disinfection and instead embracing UV lights for HVAC systems: “In today’s air-conditioned hospitals, the best location for UV devices is typically not in the upper air but inside the air handling units (AHUs), facing the cooling coils. Why is this a better solution? Hospitals today have an average of 15 to16 air changes per hour. During this time, virtually all the air within the occupied space – and the infectious organisms contained within that air – travel through the AHUs. Thus, through the normal building air recirculation process, you are bringing those infectious organisms directly to the germicidal UV lights, which penetrate their DNA to kill or inactivate them. This is a more efficient and effective approach to infection control than upper-air UVGI systems. Using UV in the AHUs has another very important advantage. At the same time it is cleaning the air of harmful microbes, it also destroys mold and biofilm that are universally present on the surfaces of the A/C coils. By keeping coils and other components in a constantly clean state, UV devices help AHUs to run more efficiently, with proven annual energy savings in the 15 percent range. The need for chemical cleaning or pressure-washing of coils is also greatly reduced or eliminated. Through these savings, the devices typically pay for themselves in six to 12 months while delivering ‘green’ benefits.”
Dunn notes, “Many UV devices today are designed specifically to keep cooling coils and drain pans in air conditioning free from microbial contamination, although keeping surfaces in HVAC systems clean can reduce mold spores and other surface contamination from becoming airborne in healthcare facilities, they are not a proper design for air disinfection on the fly, as many will claim. Properly designed UV air disinfection systems can remove contaminate up to 3-log in a single pass in an HVAC system and improve indoor air quality throughout a healthcare facility, air disinfection systems simultaneously disinfect surfaces in line of sight of the lamps, while surface disinfection systems do not simultaneously disinfect passing air in levels adequate to properly remove contagion. Congregate settings in hospitals (emergency departments, waiting rooms, corridors, cafeterias, etc.) can benefit from the additional implementation of upper air UVGI to reduce contaminate in the rooms where is generated, while safely allowing humans to occupy the space.”
Stratham emphasizes that although air disinfection is important in the reduction of HAIs, the most important way to impact disinfection in the environment of care is through the frequent and thorough disinfection of surfaces. “Organisms such as Clostridium difficile, vancomycin-resistant Enterococcus, methicillin-resistant Staphylococcus aureus, Acinetobacter, Klebsiella and other Extended Spectrum Beta-lactamase-producing Gram-negative rods do not stay airborne for a significant length of time,” Stratham says. “These are the primary causes of resistant infection within the healthcare setting and they are not considered airborne pathogens.
Recently I read a great quote from a research article regarding VRE: ‘Subsequent transfer of VRE to a clean site on a patient or in the environment occurs with comparable efficiency regardless of whether the source of contamination is a patient or an environmental site.’1 What a great way to make it clear as a bell. It appears to be an easy problem to solve, but it is not. Chemical application for environmental disinfection is rarely carried out properly due to time and labor resources. Often wiping with a disinfectant wipe is all that can be carried out. This is not a true disinfection process, but resources are limited. The specified wet dwell time is difficult to achieve, spots are missed, and organisms are transferred. I have seen colonization risk hazard ratios as high as four for ICU rooms that were occupied by a colonized patient previous to the current patient. This means that the patient is four times more likely to become colonized or infected in the next measured timeframe. The risk becomes exponential; over time it is easy to see why we have a problem.”
Stratham continues, “For these reasons, I am biased toward surface disinfection as the most important environmental aspect of reducing hospital-acquired infections. I believe we can cut benchmark rates in half if we eliminate the environmental reservoir of hospital pathogens. This is a bold statement, but when you consider the cumulative effect of breaking the chain of colonization and infection, we can see multiple compression in the HAI rate rather than the expansion we have seen in the last 10 years. Strategically thinking healthcare facilities are implementing automated technologies to deal with this reservoir or increasing their labor expense and environmental protocols to address it.”
1. Hayden MK, Bonten JM, Blom DW, Lyle EA, van de Vijver D, Weinstein RA. Reduction in acquisition of vancomycin-resistant Enterococcus after enforcement of routine environmental cleaning measures. Clin Infect Dis. 2006,42:1552-60.