Infection Control & Hospital Epidemiology
the pulsed-xenon device had much lower UV-C irradiance (10.8 µW/cm2). The pulsed-xenon device generated a spectrum with peak irradiance of 309.4 µW/cm2 in the UV-A range of 320– 399 nm; 2 pulsed-xenon devices were tested with nearly identical irradiance results. For the nonstandard device with 3 vertical towers, measured UV-C irradiance with 1 tower directed at the detection device was higher than the output of the standard devices; however, during routine operation, the towers of this device rotate to deliver UV to all areas of the room. The non- standard device with adjustable bulbs had lower measured UV-C output (26.2 µW/cm2) than the standard devices. Figure 3 shows the mean log10CFU reductions of the patho-
gens for each of the standard vertical tower devices after 4 min- utes of UV-C exposure. All low-pressure mercury devices reduced recovery of each of the pathogens significantly more than the pulsed-xenon device (P<.0001 for all comparisons). The per- formance of the 4 low-pressure mercury devices was similar with ~2 log10CFU or greater reductions in VRE and MRSA and ~1 log10CFU reduction in C. difficile spores. However, device 2 treatment did result in overall reductions that were significantly greater than devices 3 and 4 (P ≤ .02), but not device 1. Figure 4 shows the mean log10CFU reductions of the patho-
gens for the nonstandard devices after 4 minutes of UV-C exposure. By ANOVA, there were no significant differences among the 3 nonstandard devices. The adjustable device with bulbs oriented vertically is shown for comparison but was not included in the analysis. The overall reductions for the
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nonstandard devices were equivalent to or greater than the reductions achieved by the standard vertical tower devices. Each of the devices achieved ~3 log10CFU reductions in C. difficile spores at the head of the table positions.
Discussion
In a point-prevalence culture survey, we found that contamina- tion of radiology tables with healthcare-associated pathogens was not uncommon. Exposure to a 4-minute treatment cycle with 5 standard vertical tower UV-C room decontamination devices was effective in reducing pathogens on carriers in multiple sites on a radiology procedure table. However, the 4 low-pressure mercury devices were significantly more effective than the pulsed-xenon vertical tower device. Nonstandard devices with adjustable bulbs, a robotic base that moves beside the table during the cycle, or with 3 towers, were at least as effective as the standard devices. Each of the devices required <1 minute to move into position and complete the set-up needed to begin a UV cycle. These results suggest that many UV devices that are currently available could provide an effective and efficient adjunct to manual cleaning and disinfection in radiology procedure rooms. Our findings are consistent with 3 recent reports in demon-
strating that measurements of irradiance may be useful in understanding decontamination performance of different devi- ces.20–22 If a radiometer is available, measurement of irradiance can be completed quickly and easily. Alternatively, commercial test cards can provide a simple and easy-to-use colorimetric assessment of UV output.20,21 Such measurements can provide comparative data for different devices, assess delivery of UV to different sites in patient rooms, and confirm that devices are operating correctly. Although manufacturers may suggest that some devices have
features that enhance efficacy, the 4 standard low-pressure mer- cury devices that were tested had similar irradiance readings and were similarly effective in reducing pathogens on carriers. The pulsed-xenon device provided much lower UV-C output with higher UV-A output and was less effective in reducing pathogens on carriers. A previous study also demonstrated that a pulsed- xenon device was less effective in reducing pathogens on carriers than a low-pressure mercury device.5 However, pulsed-xenon devices have been shown to reduce bacterial contamination on surfaces in patient rooms, and use of the device has been asso- ciated with reductions in VRE and C. difficile infections in some quasi-experimental studies.5,6 The nonstandard devices that were tested are intended to
Fig. 2. Comparison of irradiance measurements for (A) the standard and (B) nonstandard ultraviolet light devices. Irradiance measurements were taken at a height of 86.4 cm from the floor and 91.4 cm from the light-emitting portion of the devices. The average absolute irradiances in µW/cm2 for the UV-C (250–279 nm), UV-B (280–319 nm), UV-A (320–399), and visible light (400–800 nm) were calculated based on readings taken over several seconds. For the nonstandard device with 3 vertical towers, the irradiance for 1 of the towers was measured with the bulbs in a fixed position directed at the detector.
allow increased proximity to the sites of contamination and/or to improve exposure in shaded areas. One notable finding was that the device with adjustable bulbs was as effective as the standard low-pressure mercury vertical tower devices despite having sub- stantially lower measured irradiance. The ability to extend the adjustable bulbs of the device horizontally over the table increases proximity to the sites where carriers were placed. The same device was also effective when deployed as a robotic device that moves along the side of the table during the treatment cycle. One potential limitation of the adjustable and robotic devices is that they required more time to set up than the standard devices. The standard low-pressure mercury vertical towers achieved
only a ~1 log reduction of C. difficile spores with a 4-minute cycle. One approach to address this deficiency of these devices might be to provide a longer cycle time after procedures are completed on
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