Far-UV Light Disinfection of Hospital Computer Keyboards

Author's note: This article is based upon work supported in part with funds provided by the VA National Center for Patient Safety plus resources and the use of facilities at the VA Central California Health Care System.

Electronic equipment such as computer keyboards that is shared and touched frequently by hospital caregivers in patient-care areas have been shown to harbor a variety of bacterial and viral pathogens. These devices serve as significant vectors of transmission for such organisms. Computer users unconsciously touch their eyes, mouth and nose while typing, and are sometime neglect to wash their hands after providing patient care. Unfortunately, such equipment is difficult to clean and disinfect, due to the potential damage caused by water-based cleaning products and the difficulty and time spent in wiping and drying all exposed and irregular surfaces.

Ultraviolet (UV) radiation has been a known mutagen at the cellular level for more than a century. The lethal action of sunlight on certain bacteria (known as ultraviolet germicidal irradiation) was demonstrated as early as 1877. Studies in the 1940s and 1950s examined the effect of artificial UV light on specific species of bacteria in laboratory settings. Practical applications of this technology have focused mainly on purification of water and in air handling systems. A literature review shows that use of UV light disinfection of surfaces in healthcare settings has thus far been limited to clinical laboratory work surfaces and equipment.

Recent studies have shown that specific wavelengths and exposure times of ultraviolet light can effectively kill strains of bacteria in both laboratory cultures and animal tissue. At certain wavelengths, UV light will break the molecular bonds within micro-organismal DNA, thereby destroying them, rendering them harmless or prohibiting growth and reproduction. Investigators have also tested the effectiveness of traditional disinfectants commonly used in hospitals to clean computer keyboards. The most effective disinfectant was one in which the solution remains on the cleaned surface for at least ten minutes before it is wiped off. This potentially puts the keyboard unusable for ten minutes on a busy nursing unit, and the process of application and wiping or air-drying is time-consuming. In addition, from an environmental standpoint, the volatile organic chemicals emitted as gases from certain liquid disinfectant solutions may have short- and long-term adverse health effects when released into the environment, presenting a potential danger to both workers and patients. Clearly, alternative safe and efficient disinfection methods are desirable.

There have been no published studies examining the effectiveness of UV light on the reduction of bacteria on the surfaces of shared patient care equipment. With increasing use of electronic patient records and interdisciplinary email communication, the use of computers by the hospital clerical and patient care team is increasing. Perhaps no other item in today’s hospital that uses a totally electronic patient record is touched by more staff in a typical day than the shared computer keyboard.

This study sought to examine the effectiveness of using ultraviolet light to disinfect shared hospital computer keyboards that are in daily use on a variety of active patient care units and clinics, thus showing that such technology is an acceptable, economical, environmentally-friendly, and superior method of disinfection in healthcare facilities. This project was reviewed and approved by the VA Central California Health Care System Research and Development Committee. The shielded Far-UV emitting device that was the center of the study, the Sterilray ™ (formerly named the “Germbuster”) Sanitation Wand, is manufactured by Healthy Environment Innovations, Inc. The four-pound wand, attached to a rolling power pack, can be operated easily and safely by a single person trained and certified in its use and safety precautions.

The Sterilray ™ wavelength is in the Far-UV band with much more photon energy than mercury based 254nm UV-C bulbs. Sterilray ™ targets the nitrogenous bases in the DNA that have higher absorbance for this wavelength. Sterilray ™ emits a Far-UV wavelength and claims to destroy the DNA of bacteria and viruses with an average “kill rate” of log 3 per one second exposure. With recommended eye protection, it can be used quickly and safely, requiring a pass of the sanitation wand of one second per every foot of surface to be disinfected. However, an estimated two second pass was utilized for this study (which would therefore result in a predicted log 4-5 reduction of most strains of bacteria).

The study design was experimental, randomized, non-blind, and prospective in nature. A t-test was used to test the hypothesis that there is a significant difference in the presence of bacteria on keyboards treated with Far-UV light compared to non-treated keyboards. Fifty keyboards, divided between an outpatient clinic area, medical/surgical unit, and intensive care unit, were randomly matched and distributed into treatment and control groups. Keyboards were tested from computers at nurses’ stations and in examination rooms, unit and clinic clerical and check-in desks, on medication carts (using barcode medication administration keyboards) and in charting rooms used by nursing staff, physicians and other clinical staff such as dieticians. All treatment group keyboards were treated with Far-UV disinfection twice a day on each weekday (holidays excepted) by two certified hospital Environmental Services staff, once at approximately 7 a.m. and once at noon. These times avoided the busier times of the day on these areas, thus minimizing interruptions to staff using the computers. Keyboards to be treated were identified with a brightly colored sticker in one corner. Control group keyboards were not stickered.

A dry culture of the surface of the letter “H” key on keyboards was obtained each day, using a dry, sterile cotton tipped applicator rubbed over the top surface of the key in five or six firm strokes, and transferred by streaking, while rolling the applicator, to numerically coded tryptic soy based (TSA) sheep’s blood agar plates. Only one person did all the cultures, to assure continuity of technique. Cultures were obtained at times ranging from one hour to four hours since the previous treatment, with 10 keyboards cultured per day. The letter “H” was cultured since this key is a frequently touched key by most people (being right-handed) and also because typing of this key requires one to use the index finger, which is used to pick up objects, turn doorknobs, etc.

Thus, each of the 50 keyboards was cultured once per week. Eight weeks of cultures were obtained (eight weekly cultures of each of the 50 keyboards, for a total of 400 cultures). The culturing schedule was modified every few weeks, so that any one keyboard was not cultured on the same day each week. The hospital laboratory did not know from which location the coded cultures were obtained, nor if they came from a treated or control keyboard. Colony counts were done by the lab using their standard bacteriology methods of incubation and colony counting. A baseline measurement period of all devices was done for four weeks prior to initiation of treatments to assess baseline bacterial growth on all keyboards and confirmed that there was no significant difference between the control and treatment groups prior to initiation of the treatment period.

Standard recommended safety precautions were taken while using the Sterilray. Staff members in the immediate area were asked to look away from the light while it was briefly on. The device also has a built-in safeguard to overexposure in that it will turn itself off immediately if the lamp is raised more than four inches from the treated surface. Thus any incidental exposure was to surface-reflected light only. The operator is required to wear long sleeves, gloves, and eye protection to avoid possible skin or eye damage from long-term exposure.

The times of treatments and times of culturing were recorded throughout the study. The laboratory maintained an ongoing list of cultures by code number, date, species of bacteria, and number of colonies. The most common species present was, not surprisingly, coagulase-negative staph, which accounted for 97 percent of the colonies grown. Though two cultures grew Staphylococcus aureus, neither was MRSA. Analysis compared the average bacteria colony growth of cultures from the treated and control cohort groups as a whole, as well as between the three patient-care areas.

There was a significant difference in average colony counts between the treatment group (5.91) and control group (11.62). The average colony count of the treated group was thus 49 percent less than the control group. The difference was most pronounced between keyboards in the intensive care unit. This was possibly due to the lower number of staff sharing keyboards in the area. On the medical/surgical unit, keyboards were used by a larger number of staff and were in use more of the time, thus the number of staff using an average keyboard in the time period following its last treatment was higher. The average colony count of the treated group predictably decreased as time between culture and previous treatment increased.

There is the potential for further study of the effectiveness of Far-UV light disinfection, including

• Comparing different exposure times or frequencies

• Measuring effectiveness on other care area surfaces, such as desks and phones

• Measuring effectiveness on disinfection of MRSA patient room surfaces

Greg Wike, MA, RN, is patient safety manager in the Office of the Director at the Department of Veterans Affairs Central California Health Care System in Fresno, Calif.

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