How to Select an Ideal Disinfectant
By: Lee Nesbitt, BMSc
With the emergence of new pathogens and potentially more virulent strains of well known pathogens, the utilization of appropriate disinfectant products has become exceedingly important. However, there is much more to consider than simply if the chosen disinfectant product carries effectiveness against a particular organism. The Centers for Disease Control and Prevention (CDC)'s "Guideline for Disinfection and Sterilization in Healthcare Facilities" (2008) has identified several of the key criteria that should be carefully measured when evaluating a disinfectant product or chemistry. Although this best practice guideline's intended audience is human health, the information found within can certainly be interpreted and applied to animal health institutions as supported by Dr. Kate Hurley, Shelter Medicine Program Director at the University of California, Davis in her presentation titled "Saving lives through sanitation". Dr. Hurley discusses that no single disinfectant is perfect, and that when choosing a disinfectant one must look at the toxicity properties, spectrum of effect, contact time, detergent activity, affects of organic matter and stability.
Speed of Disinfection
It may be surprising for some to hear, but disinfectants do NOT terminally disinfect on contact. Each product requires a specific length of time that it must remain wet on a surface to achieve complete disinfection. This is known as the "contact time" and it will be clearly listed on the label of registered disinfectant products. To ensure terminal disinfection, the contact time MUST be complied with. Products that dry before this contact time is achieved - whether because it is too long (ie. 10 min) or because the product itself contains solvents or alcohols causing it to evaporate rapidly despite having a short in-vitro contact time – will not achieve complete disinfection. Therefore, ideal disinfectant chemistries and products will offer rapid and realistic contact times. This ensures compliance and ultimately instills confidence that disinfection will be achieved.
Spectrum of Microbicidal Efficacy
The war we wage against microbes is one fought against an invisible enemy. Unfortunately, it is impossible for us to easily identify which microorganisms are present on a surface at any one time. This begs the question, how can we rightfully employ disinfectant products that ONLY exhibit effectiveness against a narrow spectrum of bacteria and easy to kill viruses? How are we addressing more difficult to kill pathogens such as Canine Parvovirus or Feline Calicivirus when we use these narrow spectrum products? Ideal disinfectants will demonstrate a broad antimicrobial effectiveness, ultimately preventing the environmental transmission of a wide variety of microorganisms including potentially resistant strains.
The cleaning efficacy of a disinfectant is an oft over-looked attribute. Perhaps not as glamorous as the spectrum or speed of kill, the cleaning efficacy – or lack thereof – of a disinfectant has the potential to affect the entire disinfection process. Environmental infection control best practices clearly recommend that cleaning should precede the disinfection of a surface or item. Dust, dirt and organic soil can create protective reservoirs for pathogens if not effectively removed. Using a disinfectant that is considered an effective cleaner not only has the potential to remove the need for adding secondary cleaning products but also provides added confidence, that in situations when a formal cleaning step has been missed or inadequately performed, the disinfectant itself will remove soil allowing disinfection to occur. Often this is achieved with the inclusion of surfactants within the product's makeup. Surfactants not only enhance the cleaning efficacy of a product but also assist in ensuring complete and even coverage on a surface, preventing beading that occurs with many liquids. Even coverage = Even disinfection.
Personal Health and Safety
As our infection control needs grow beyond traditional settings such as hospitals and into the community, so does our use of chemical disinfectants. The resulting increased exposure amplifies our need for safer chemistries. Preferably, disinfectant chemistries should be Volatile Organic Compound (VOC) free, meaning no noxious fumes are emitted, non-toxic, non-irritating to skin, eyes and respiratory and non-sensitizing. Unfortunately, most disinfectant chemistries are required to compromise their overall efficacy as a germicide in order to comply with enhanced safety needs or vice-versa, compromise their safety profile to achieve broad spectrum germicidal efficacy. An ideal disinfectant will strike a balance between safety and efficacy without compromise.
Much like our personal health and safety, the increased exposure of disinfectant chemicals to the environment amplifies the need for more environmentally preferable chemistries. Disinfectants by definition are chemicals designed to destroy vegetative forms of harmful microorganisms. This simple definition has caused many to believe that environmental sustainability or preferability of a disinfectant is simply a chemical impossibility. While this may be true of certain legacy disinfectant chemistries which exhibit their effectiveness on microbes in a way that is also toxic to aquatic life, newer technologies have determined ways to effectively eliminate pathogenic microbes by means that are more environmentally preferable. Just like microbicidal claims are validated by third party analysis, claims of environmental preferability should also be scrutinized. While the United States Environmental Protection Agency (EPA) does not currently allow "Green" claims on most registered disinfectants, there is a shift occurring within the agency to possibly change this policy under their Design for the Environment (DfE) program. The DfE has undertaken a pilot project that will allow only those disinfectants with hydrogen peroxide, lactic acid or citric acid as their active ingredient to display claims of environmental preferability provided their attributes fall within some very set parameters.
In an ideal world, a single effective disinfectant product would be available for use on all surfaces. Unfortunately, NO disinfectant chemistry is 100% compatible with all surfaces. In our own homes, we would never think of using a bathroom cleaner to clean our windows, wooden table and leather furniture. So why is it that we expect to use a single disinfectant product on all surfaces within an institutional setting? The majority of surface disinfectants in use today do carry good material compatibility profiles when used as intended, however, certain applications or surface substrates may require unique attention. Most often, simply the implementation of distinct protocols is a sufficient means for addressing the issue. However, in extreme cases a task oriented product or physical barriers may be required.
In summary, an ideal disinfectant should excel in all of the major decision making criteria. The disinfectant should effectively clean, thereby removing dirt and soil from the surface. It should be effective against a broad spectrum of microorganisms (bacteria, viruses, etc.) in a rapid and ultimately, realistic contact time. Finally, it should be safe for the users and the occupants of the environment as well as the environment itself.
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