An Analysis of Ultraviolet-C Light Irradiation in Reducing Bacterial Contamination of the Anesthesia Work Area

Surgical site infections are associated with increased patient morbidity and mortality.  At the University of Iowa (Iowa City, Iowa) and Georgetown University (Washington, D.C.), there were surgical site infections for 12% (13 of 106) with Staphylococcus aureus transmission detected among anesthesia workspace reservoirs versus 2% (8 of 406) without.  The anesthesia machine is a potent transmission vehicle for more pathogenic strain characteristics such as S. aureus sequence type 5. 

Ultraviolet-C irradiation may help to reduce environmental contamination of the anesthesia work space.  Important considerations include distance of the environmental surface and/or equipment from the emitters, orientation of the target surface(s), a clinically relevant log reduction, target pathogen(s), and a minimal effective dose to reduce photo reactivation and dark repair.  While a clinically relevant cleaning threshold for the anesthesia workspace is less than 100 colony-forming units  a ultraviolet-C irradiation dose and configuration effective in reducing contamination below this threshold has not been established. We aimed to address these limitations.

A linear configuration of three ultraviolet-C irradiation emitters (Surfacide, USA; Fig. S1, https://links.lww.com/ALN/D612) positioned side by side, each rotating 5°, was deployed for direct irradiation of S. aureus American Type Culture Collection 6538 carriers and radiometers positioned at three locations (left, center, and right) on an aluminum stand at 9 feet from the center emitter and at 47.5 inches (120.65 cm) from the floor. Carriers and radiometers were exposed to an increasing dose of ultraviolet-C irradiation from 27 to 253 mJ/cm², where dose is irradiance * time of exposure. The lowest dose effective in achieving a 6-log or greater reduction was 27.01 ± 0.15 mJ/cm² (table 1).

The lowest effective dose was then applied to S. aureus sequence type 5 carriers using a triangular configuration of three emitters each rotating 360° (Fig. S2, https://links.lww.com/ALN/D612). Carriers were positioned at variable heights (25.5, 47.5, 58.5, and 69.5 inches) and orientations (45, 90, and 180°) to account for variability in the anesthesia workspace (Fig. S3, https://links.lww.com/ALN/D612). A 2-min disinfection cycle was initiated for 126 carriers, including 108 treatment (S. aureus sequence type 5), and 18 controls (S. aureus sequence type 5–positive and sterile H20–negative), where 9 pairs provided adequate power to confirm adequate disinfection. Residual colony-forming units were quantified. Treatment reduced S. aureus sequence type 5 colonies (0 for 9 of 9 samples versus 19 to 128 among the 9 controls) for 9 of 9 pairs, binomial test (P = 0.0039) with a 6-log or greater reduction (undetectable) achieved for all other positions (Table S1, https://links.lww.com/ALN/D612).

Emitters were positioned in triangular or linear configurations about an aluminum stand at 9 feet, and a 2-min treatment cycle was initiated. The irradiance dose was recorded for all carrier positions (25.5, 47.5, 58.5, and 69.5 inches from the floor and oriented at 45, 90, and 180°). The triangular ultraviolet-C irradiation configuration delivered a lower dose of irradiation than the linear configuration at 69.5 inches from the floor and with horizontal orientation (mean 1.88 ± 0.44 mJ/cm² for nine observations triangular vs. mean 0.70 ± 0.52 mJ/cm² for nine observations linear; P < 0.0001; Wilcoxon–Mann–Whitney test; fig. 1).

Fifty-two distinct operating room environmental sites were sampled before and after a 21-min treatment cycle with triangular configuration and colony-forming units compared via the Wilcoxon–Mann–Whitney test. Treatment was associated with a reduced proportion of sites returning 100 colony-forming units or more (42% [22 of 52] usual care to 2% [1 of 52] treatment; Fisher exact P < 0.0001). There were 10,125 ± 19,139 colony-forming units after surface disinfection but before ultraviolet-C irradiation versus 31 ± 253 colony-forming units after surface disinfection and ultraviolet-C irradiation (Wilcoxon–Mann–Whitney P < 0.0001; Table S2, https://links.lww.com/ALN/D612). Twenty-four sites failed terminal surface disinfection cleaning, while only three failed ultraviolet-C irradiation treatment (Table S3, https://links.lww.com/ALN/D612). Residual pathogens after surface disinfection and after ultraviolet-C irradiation are shown (Table S4, https://links.lww.com/ALN/D612).

A review of ultraviolet-C irradiation efficacy for augmentation of terminal cleaning evaluated 12 studies.  One study involved the operating room, but there were no studies that specifically assessed the anesthesia workspace. Delivered dose at variable heights and orientations was not assessed, and treatment times ranged from 2 to 55 min. Most studies focused only on a percent reduction in total colony-forming units versus on a clinically relevant log reduction or attenuation of target pathogens.  Clark et al. showed that improved surface disinfection cleaning during patient care can reduce the proportion of measured environmental sites returning 100 colony-forming units or more from 46% to 12%.  Their study did not address ultraviolet-C irradiation, terminal cleaning of the anesthesia workspace, more pathogenic strain characteristics, or infection development. 

In this study, we have added to this body of literature by establishing the efficacy of ultraviolet-C irradiation for the more pathogenic strain characteristic S. aureus sequence type 5, characterizing an ultraviolet-C irradiation configuration effective in delivering a minimal dose for S. aureus sequence type 5 and American Type Culture Collection 6538 attenuation, identifying a clinically relevant log reduction for the operating room, and demonstrating clinical relevance of the triangular configuration for whole operating room disinfection. We show that surface disinfection cleaning is more likely to fail than ultraviolet-C irradiation for a variety of objects and surfaces in the operating room, providing the impetus for increased use of ultraviolet-C irradiation to augment terminal surface disinfection cleaning efforts.

A hospital with five operating rooms may provide care for 2,750 surgical patients annually. With a surgical site infection incidence of 11%  and an average cost of $31,600 per infection this could amass to 302 surgical site infections and $9.5 million annually. Improved disinfection of the anesthesia work area using a multifaceted approach including ultraviolet-C irradiation technology can reduce surgical site infections by more than 80%.  With the cost of the studied ultraviolet-C irradiation system being $95,000, behavioral interventions $13.6 per patient ($37,400), and a fixed annual cost of $120,000 for surveillance optimization of the employed interventions the combinations of technologies is net cost-saving.  We recommend daily implementation of the ultraviolet-C irradiation technology as described in this study, 2 min using the triangular configuration, to augment terminal cleaning of the anesthesia work area for each operating room, in addition to optimization of provider hand hygiene, patient decolonization, and vascular care. 

Future work should determine whether the described impact is dependent on previous surface disinfection. If independent, the impact of ultraviolet-C irradiation could be extended to reduce exposure to harmful chemicals, which could further reduce cost of labor and supplies.

In conclusion, 2 min of triangular ultraviolet-C irradiation configuration treatment can generate substantial S. aureus sequence type 5 reductions with indirect exposure while reducing the delivered dose. Such brief periods have substantial opportunity to attenuate the spread of more pathogenic S. aureus strain characteristics among anesthesia workspace reservoirs and in turn, subsequent surgical site infection development.