Table 2. Impact of ultraviolet-C (UV-C) delivery configuration and height on Clostridioides difficile attenuation.
Configuration one (three towers positioned triangularly each rotating 360 degrees), configuration two (one tower rotating 360 degrees), configuration three (three towers in a line, each rotating five degrees), configuration four (one tower rotating five degrees), and configuration five (one emitter rotating 90 degrees). All carriers were oriented vertically to the emitters, mJ/cm2 was the dose of irradiation delivered to the carriers at 25.5 or 69.5 inches from the floor. SD = standard deviation, positive ctrl (control) was the average of the colony-forming units (CFU) for each of two dilutions (10-6 and 10-7) for each of the three carrier positions (A, B, and C) on the aluminum stand positioned in front of the emitters at a distance of 9 feet (initial CFU), N=6 for the average. The same applies to UV-C CFU/mL at 25.5 and 69.5 inches (final CFU). LR = log reduction defined by log10 (initial CFU/final CFU). For example, log10 (3.25 x 107/3.33 x 105) = 1.99. The average LR refers to the average LR for the two heights at a given dose, for example, 1.99 + 6/2 = 4.
| Config | 25.5 in mJ/cm2 | SD 25.5 in mJ/cm2 | 69.5 in mJ/cm2 | SD 69.5 in mJ/cm2 | Positive Ctrl CFU/mL | UV-C 25.5 in CFU/mL | LR | UV-C 69.5 in CFU/mL | LR 69.5 in | Average LR 25.5 and 69.5 in |
| One | 447.91 | 28.56 | 440.83 | 18.69 | 3.47 x 107 | 0 | >6 | 0 | >6 | >6 |
| Two | 446.10 | 16.92 | 430.38 | 4.28 | 1.30 x 108 | 0 | >6 | 0 | >6 | >6 |
| Three | 442.01 | 16.99 | 449.66 | 21.65 | 1.11 x 108 | 0 | >6 | 0 | >6 | >6 |
| Four | 448.75 | 24.31 | 444.33 | 16.87 | 1.54 x 108 | 0 | >6 | 0 | >6 | >6 |
| Five | 444.41 | 19.95 | 434.38 | 14.53 | 3.25 x 107 | 0 | >6 | 3.33 x 105 | 1.99 | 4 |