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Wednesday, August 31, 2011

Premature Evaporation: Is your disinfectant fulfilling your every desire?

The use of disinfectants remains the backbone for environmental decontamination and infection control in multiple industries including laboratories, healthcare, educational and institutional settings to name a few. Numerous peer reviewed studies have confirmed that the environment can play a role in the transmission of microorganisms and therefore thorough attention to cleaning and disinfecting is required to minimize this as a source of contamination. Unfortunately, the requirements for the effective use of most disinfectant chemistries are often very difficult to comply with under real-life conditions.

Instructions for the proper use of a disinfectant are indicated on the label of any EPA or Health Canada registered product. Diligent compliance of these instructions is necessary for proper and complete disinfection. This is particularly true of the contact time indicated on the label. The contact time or dwell time is the length of time that the surface must remain wet with the disinfectant in order to achieve the microbicidal kill as indicated on the label. Many would argue that this is the most critical step in the disinfection process. However, current practices generally only allow time for a surface to be wiped once and allowed to air dry. This begs the question – what are the potential implications of this practice when employed with the most commonly used disinfectant chemistries?

In a recent edition of the Journal of AOAC International (Vol. 93, No. 6), Dr. Navid Omidbakhsh, VP of Open Innovation at Virox Technologies Inc., expertly studied the level of kill actually achieved using the practices that are routinely used by disinfectant end users – wipe once and allow the surface to air dry. The study compared six different disinfectant chemistries: a Quaternary Ammonium Compound (Quat), a Quat-Alcohol blend (2 concentrations of alcohol), a Phenol, a Phenol-Alcohol blend, Bleach (Sodium Hypochlorite) and Accelerated Hydrogen Peroxide. Each disinfectant chemistry was tested at its recommended use dilution to determine its performance in the following criteria: drying time and bactericidal activity during that period of time.

First, the drying time of each disinfectant was determined and compared to the product’s label contact times. It was found that all disinfectants dried in less than 5 minutes with alcohol and solvent containing products drying significantly faster (less than 1 minute – some as quickly as 30 sec.). Of the chemistries tested, only a single product actually remained wet for a longer period of time than indicated on the label. Am I the only one that finds this concerning? Certainly any product that dries too quickly can be re-applied, but what are the chances of that actually occurring? Would you be confident that disinfection is being achieved with those types of disinfectants? (Figure 3 in the published study provides excellent visual comparison of the data.)

The second phase of the study tested the realistic microbicidal efficacy of each disinfectant by measuring their effectiveness against 2 key strains of bacteria at the contact time determined in the first phase of the study. For example, it was determined that Bleach dried in 3 min., therefore its bactericidal efficacy was tested at the 3 min contact time rather than the label contact time of 10 min. Not surprisingly, the only chemistry to remain wet for longer than its required contact time was the singular chemistry to achieve full bactericidal efficacy (>6 log reduction) across both strains of bacteria that were tested. The remaining chemistries all fell short of achieving true disinfection. The most alarming of which were the products containing higher concentrations of alcohol (60-70% ethanol blended with quat and/or phenol). These products dried exceedingly quickly (30 sec. or less) and in that period of time elicited minimal germicidal efficacy on the bacteria. Despite remaining wet for upwards of 3 min. the same was also true of the concentrated quat and phenol products that carried 10 min label claims. They only achieved <2 log and <3 log reduction respectively. So our suspicions have been confirmed. Disinfectants that do not remain wet for their entire contact time after a single application do not achieve disinfection. With this knowledge, how will you address the disinfectants that may be in use at your institution? Protocol revision to ensure the disinfectant stays wet for the required period of time? Change of disinfectant to a chemistry/product that does remain wet for the required period of time without major protocol changes? (Refer to Tables 3 & 4 in the study for the complete results.)

In summary, Dr. Omidbakhsh’s study highlights the importance of selecting a disinfectant that will perform under real life conditions. As the study findings illustrate, most disinfectant chemistries are unable to elicit their full and complete effectiveness because they simply do not remain wet on the surface for a sufficient period of time. Rapid and realistic germicidal effectiveness provides end-users with the comfort and confidence that their disinfection needs will be met on a regular basis.


Omidbakhsh N. Theoretical and experimental aspects of microbicidal activities of hard surface disinfectants: are their label claims based on testing under field conditions? J of AOAC Int. 2010;93:6:1-8. http://www.virox.com/download.aspx?ItemInfoID=474

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