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0.4% mucin, and 5% bovine serum albumin were spread to cover 20-mm diameter circular stainless-steel carriers and allowed to air dry. The carriers were adhered to petri dish lids. The computed tomography table was set to a height of 40 inches from the floor; an additional test with the table lowered to 20 inches was con- ducted for a pulsed-xenon device because the bulbs were located lower to the ground than the other devices. Carriers were placed in 5 locations on the table (Fig. 1). The carriers placed at the foot of the table and the mid-point of the table were oriented horizontal to the floor. Given the complex configuration of a headpiece used to hold the patient’s head during computed tomography of the head, 3 carriers were placed at this location including 2 vertically oriented carriers (ie, perpendicular to the floor) inside the left and right wings of the headpiece and 1 horizontally oriented carrier in the center. For the purposes of the study, the devices were classified as
either standard vertical tower devices or nonstandard devices. For the standard vertical tower devices, the device has 1 tower with vertically oriented bulbs and is stationary during operation. Five standard vertical tower devices were tested, including 4 low- pressure mercury devices and 1 pulsed-xenon device. Three nonstandard devices were tested. The first nonstandard device has 3 vertical towers that are intended to run simultaneously to reduce the impact of shadowing when operating in a hospital room. Each tower directs UV light in 1 direction and can be rotated from side to side to provide coverage of surfaces in a patient room or can be in a fixed position to focus on areas of interest. The second nonstandard device has 3 adjustable lamps that can be oriented to provide closer proximity to the surface of interest. The final nonstandard device was a robotic mobile device that moves along the side of the table during the treatment cycle. The robotic device was the same as the device with 3 adjustable lamps but with a robotic base that moved the device in a straight line along the side of the table during the treatment cycle. The standard vertical tower UV devices were placed near the
head of the table (Fig. 1). The device with the adjustable lamps was placed in the same location but the lamps were extended horizontally over the table to provide closer proximity to the table surface and to minimize potential shadowing in the head piece. For the device with 3 vertical towers, 1 tower was placed on each
Jennifer L. Cadnum et al
side of the head of the table and 1 was placed at the foot of the table. For the purposes of this study, the device with 3 vertical towers was set such that each tower was in a fixed position facing directly at the table with no rotation. The robotic unit was set to move slowly alongside the table during the 4-minute cycle starting at the foot moving to the head of the table. Each device was run for a 4-minute treatment cycle; this
duration was chosen based on discussions with radiology department staff regarding cycle durations that might have a limited impact on patient flow and because 1 UV device company recommends a 4-minute cycle for radiology departments. After the UV treatment, the carriers were collected and viable organ- isms were quantified as previously described.19 All tests were performed in triplicate, and reductions for test carriers were compared with untreated control carriers. For each device, the time to position and set up the device for operation was recorded. For these assessments, the devices were placed in the corner of the room prior to the testing based on the assumption that it would be most efficient to store devices within the treatment room.
Statistical analysis
Analysis of variance was performed to compare the mean log reductions for the standard vertical tower devices and for the nonstandard devices controlling for organism and site. A post- hoc Tukey’s honest significant difference method was used to test pairwise differences between group means. Data were analyzed using SPSS statistical software version 10.0 (SPSS, Chicago, IL).
Results
Of 52 sites cultured in 10 radiology rooms, 7 (14%) were positive for 1 or more pathogens. Staphylococcus aureus and Candida spp were each recovered from 2 (4%) sites. VRE, fluoroquinolone- resistant gram-negative bacilli, and C. difficile were each recov- ered from 1 site. Figure 2 shows the irradiance readings for the study devices.
The UV-C irradiance readings for the 3 standard vertical tower devices tested were similar (range, 106.2–159.9 µW/cm2), whereas
Fig. 1. (A) Radiology computed tomography room used for the comparison of efficacy of the ultraviolet light devices. (B) Removable headpiece used for computed tomography of the head. Steel disk carriers inoculated with 106 colony-forming units (CFU) of the pathogens were placed horizontally on the body (mid-table) and foot of the table and in the center bottom of the headpiece; carriers were placed vertically on the left and right sides of the headpiece. The stationary devices were positioned adjacent to the head of the table; the distances to the carriers placed at the center of the headpiece, body of the table, and foot of the table were 91.5 cm (36 inches), 111.8 cm (44 inches), and 238.8 cm (94 inches), respectively.
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