Figure 1. Ultraviolet-C (UV-C) dose response testing for Clostridioides difficile (C. difficile) American Type Culture Collection (ATCC) 43593 carriers.

C. difficile carriers (1”x 0.9” polycarbonate, ReadyNow^TM Test Carriers, Stratix Labs Corporation, Saint Paul, MN) and calibrated radiometers (ILT1270, International Light Technologies, Peabody, MA) were mounted on an aluminum stand at three positions (A = center of stand, B = left of center of stand, C = right of center of stand) and at a height of 47.5 inches from the floor, center of bulbs. The stand was positioned at 9 feet from three low-pressure mercury gas UV-C emitters that were positioned in a row, each rotating 5 degrees. The test carriers and adjacent radiometers were exposed to an increasing dose of UV-C energy from 126.55-580.77 (mJ/cm²). Log reductions (LR) were calculated by comparing the average of treatment samples (final CFU) for a given dose to the average of positive controls (initial CFU), log₁₀ (initial CFU/final CFU). Following treatment at each target dose, carrier and control slides were removed from the cartridge and processed identically to enumerate colony-forming units (CFU). Log reductions (LR) were calculated by comparing the average of treatment samples (final CFU) for a given dose to the average of positive controls (initial CFU), log₁₀ (initial CFU/final CFU).

This image was created by the authors.