Infection Control & Hospital Epidemiology


Table 1. Use of a Continuous Visible Light Disinfection System and Predicted Reduction (%) of Common Environmental Pathogens over Timea Time (Least Number of Hours) to Achieve Sustained Microbial Reduction of Listed Percentage


Pathogen MRSA


VRE MDR-Acinetobacter C. difficile


Treatment (Light)


White Blue


White Blue


White Blue


White Blue


25% 5 2


13 2 2 2


NA 56


50% 10 3


29 5 5 4


NA 68


75% 17 6


51 9 9 9


NA NA


90% 24 10


NA 15 14 15


NA NA


Note. MRSA, methicillin-resistant Staphylococcus aureus; VRE, vancomycin-resistant Enterococcus; MDR, multidrug-resistant; NA, sustained reduction not achieved. aThe earliest hour after which the model predicts a sustained reduction of CFUs by the stated percentage for epidemiologically-important pathogens with the white light and the blue light. The largest reduction listed is 90% because the model cannot predict a 100% reduction except after infinite hours have passed.


1251


Fig. 1. Use of a continuous visible light disinfection system and predicted reduction (CFU/mL) in epidemiological important pathogens over time. Under the “blue,”“white,” and control lights, the models predicted the number of colony-forming units of (A) vancomycin-resistant Enterococcus-VRE, (B) C. difficile, (C) MDR-Acinetobacter, and (D) methicillin-resistant S. aureus-MRSA (see Methods). The curves are drawn continuously over the temporal interval from 0 to 72 hours. However, in the experiment, the actual time points when the CFUs were counted were at 0, 1, 3, 5, 6, 7, 24, 48, and 72 hours. Because the model treats time as continuous, we were able to calculate predicted values for any time point between 0 and 72.


the study room with intensity sufficient to cause inactivation of test bacteria. In both phases, the indicated lights were operated continuously (ie, 24 hours per day, 7 days per week) during the sampling period, and no other lights were present in the study room.


Study design


The vegetative bacteria were grown on sheep blood agar. Serial dilutions of inocula were made with trypticase soy broth (TSB, Remel, Lenexa, KS). The C. difficile spore preparation was stored in


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