The role of environmental disinfection in the healthcare setting is paramount in maintaining a low bioburden and helping prevent the role of fomites as a vector for disease transmission. Recent studies have shown that environmental contamination plays an important role in the transmission of MRSA, CRE, Clostridium difficile and Norovirus. For effective disinfection, users turn to Environmental Protection Agency (EPA) registered disinfectants.
Product labels for EPA-regulated disinfectants contain fundamental information for the user, such as key safety warnings and use directions. The end user must refer to this information for the careful selection of personal protective equipment, first aid in the event of an accident and contact times used for the disinfection of surfaces. Micro-organisms differ in their innate sensitivity to disinfectants, thus it is common to see varying contact times for different micro-organisms within the same use directions. Individual product labels are not all the same. While certain principle information is required, it can be difficult for the end-user to decipher the specific language used on one product versus another. Even products from the same manufacturer may carry different language and terms. Upon review of the commonly used disinfectant wipes on the market we can see a number of different iterations of use directions in the context of contact time:
“Repeated use of the product may be required to ensure that the surface remains visibly wet”
“Allow surface to remain wet for x minutes(s).”
“Allow treated surface to remain wet for x minute(s).”
“Allow surface to remain treated for the specific contact time.”
Most manufacturers suggest that the end user maintain wetness for the duration of the contact time. That appears to make sense, but there are flaws with that approach. Firstly, there is the practicality of observing wetness, especially if the contact time is long (i.e. 10 minutes) – no healthcare worker has time to watch disinfectants dry. There is also the subjectivity of dryness; is it really dry or just partially dry? Finally, consider the environmental conditions. Temperature, humidity and air flow all play a role in how fast a disinfectant (or any liquid) takes to dry on a surface.
For the truth, one needs to turn to the manner in which efficacy of disinfectants for hard non-porous surfaces are assessed by the EPA. In this case, we assess the method used for evaluating disinfectant wipes: the AOAC Germicidal Spray Test modified for towelettes, 1 although the same principal applies for other formats (i.e. sprays, dilutable liquids). Succinctly, test micro-organisms are dried upon a glass surface prior to being treated by the disinfecting wipe in a standardized manner with environmental controls. Following the desired contact time, the glass surfaces are placed in growth medium to determine the test micro-organism(s) have been eradicated. The contact time is determined based on testing by the manufacturer, but must be no more than ten minutes. During the contact time, the liquid delivered on the glass surface by the wipe is open to drying, simulating a typical healthcare environment. As such, the glass surfaces will exhibit varying levels of dryness according to the test conditions. Surfaces are not assessed for wetness* and the EPA does not require test surfaces to remain wet during the test method.
So if the disinfectant time is not the wet time, what is it?
Users should wipe down the surface and allow the treated area to remain undisturbed for the given contact time. Regardless of whether the surface is wet, dry or somewhere in between, the efficacy can be assured in line with the EPA registration.
*two exceptions include Clostridium difficile and Candida auris which are assessed using a different methodology.
1. Standard operating procedure for disinfectant test towelette testing: Testing of Staphylococcus aureus, Pseudomonas aeruginosa and Salmonella enterica. https://www.epa.gov/sites/production/files/2016-05/documents/mb-09-06.pdf
James Clayton is the Director of Laboratory Sciences for PDI.
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