To the Editor— Novel ultraviolet-C (UV-C) disinfection devices are currently flooding the infection control market due to the well-documented microbicidal efficacy of UV-C irradiation and appealing modern upgrades in mobility, safety, and monitoring of devices. This trend in the market is apparent with a quick glance through the pages of widely circulated infection control magazines, where multiple UV-C device advertisements may be present in a single issue. As noted by Cowan, at least 15 different manufacturers provide UV-C devices to the healthcare industry, but only a few devices are supported by peer-reviewed studies, and there are currently no guidelines to define what constitutes an effective level of pathogen reduction or standardized methodology for evaluating UV-C killing efficacy.

We share the concern Cowan has presented and have made efforts to bring awareness to the need for direct comparison of devices and standardization of methodology. In a recent study, we introduced the need for a platform to directly compare the many UV-C devices on the market.Reference Nerandzic, Fisher and Donskey ¹ Under uniform testing conditions, we found no difference in the efficacy of the 2 analogous UV-C devices for killing of methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant enterococcus (VRE), or Clostridium difficile spores.Reference Nerandzic, Fisher and Donskey ¹ The caveat of our findings is that the 2 devices utilized an equivalent light source (low-pressure mercury gas bulbs) and power supply, and they delivered an equivalent radiant dose. However, not all UV devices deliver similar wavelengths of light or the same strength of radiant dose.

UV radiation has peak germicidal effectiveness in the wavelength range from 240 to 280 nm.Reference Griego and Spence ^{2 –} Reference Owens, Deal and Shoemaker ⁵ Most UV devices use low-pressure mercury gas bulbs that primarily emit UV-C at 254 nm, but recently pulsed xenon flash bulbs have also been incorporated into disinfection systems. Xenon gas bulbs produce a broad spectrum of radiation that encompasses the UV (100–280 nm) and visible (380–700 nm) spectra.Reference Jinadatha, Quezada, Huber, Williams, Zeber and Copeland ^{6 –} Reference Umezawa, Asai, Inokuchi and Miyachi ⁸ In a subsequent study, we evaluated the efficacy of a pulsed-xenon device for reducing hospital-acquired pathogens on surfaces in hospital rooms.Reference Nerandzic, Thota and Sankar ⁹ While the pulsed-xenon device did significantly reduce recovery of C. difficile, VRE, and MRSA from frequently touched surfaces, it was significantly less effective than a low-pressure mercury device in reducing pathogen recovery on glass slides with equivalent exposure time, inoculum, organic load, distance from device, etc.Reference Nerandzic, Thota and Sankar ⁹ These findings suggest that not all UV devices are equally effective.

Clearly, there is a need for direct comparisons of devices, but the cornerstone to comparing UV-C devices is standardized methodology. We recently demonstrated that variation in test methods could significantly impact the performance of UV-C devices.Reference Cadnum, Tomas and Sankar ¹⁰ Factors such as increasing the surface area of inoculum spread, orientation of the carriers, and changes in the formulation of organic load greatly impacted the level of killing achieved (in some cases by >2 log₁₀ CFU, or 99%).Reference Cadnum, Tomas and Sankar ¹⁰ These findings have significant implications for the consumers of UV technologies. Without uniform testing methods, there is no baseline for the interpretation of percent or log reduction of pathogens. These examples reiterate the need for a universal set of testing guidelines to be developed by the EPA.

The efficacy of UV-C irradiation for killing pathogens is not in question, nor is the importance of testing these types of technology for reducing pathogens on hospital surfaces. However, due to the speed with which new UV-C devices are entering the market, peer-reviewed studies and standardized guidelines have fallen behind. We agree with Cowan that there is a need for uniform standards for testing the efficacy of UV-C devices. This deficiency should be addressed by regulatory agencies and the scientific community. Finally, there is a need for high-quality studies to determine whether use of UV-C devices reduces healthcare-associated infections. Currently, no published randomized trials have demonstrated that UV-C disinfection is beneficial as an adjunct to standard cleaning and disinfection.