COVID-19 AND SURFACE DISINFECTION: THE IMPORTANCE OF THE “FOUR C’S” OF DISINFECTANTS

This post is part of a series authored by the BASICS (Bold Action to Stop Infections in Clinical Settings) team. BASICS is a new initiative that will transform healthcare and reduce healthcare-associated infections (HAIs) by at least 50%.

This post originally appeared on Kinnos’ website on March 26th, and is reposted with permission.

We want to make it clear from the start that all aspects of infection prevention are crucial in the response against COVID-19: compliance with social distancing, availability of personal protective equipment (PPE), effective hand hygiene, and thorough surface disinfection, and that one isn’t necessarily more important than the other. While the media has widely reported on social distancing and (unfortunately severe deficiencies of) PPE and hand sanitizer, we feel that the nuances of surface disinfection are not frequently discussed. And having been in the disinfection space for over 5 years now, we feel pretty competent in talking about it. Kinnos has previously written about the “Four C’s of Disinfectants” in a prior blog post and we wanted to revisit some of those aspects here, which will also help people better understand how to use the EPA’s list for “Disinfectants for Use Against SARS-CoV-2”.

Before we jump into disinfection, let’s talk about COVID-19 itself. We know that COVID-19 can be transmitted through aerosolized droplets and that these droplets can land on surfaces and remain viable for hours or days depending on the surface material. We also know that COVID-19 is an enveloped virus, meaning that it’s protected by a fatty lipid bilayer. Fatty layers are easily exploited: when you wash your hands with soap, what you’re really doing is creating a fat-soluble layer for the virus’s fatty layer to bind to so that it’ll wash away with the soap. Unlike more robust pathogens like non-enveloped viruses and bacterial spores that contain layers of tough protein, fatty layers are susceptible to bonding with alcohol which causes the fat to un-bond with each other, opening up the envelope and allowing the alcohol to go in and denature proteins. Stronger oxidizing disinfectants, like bleach and hydrogen peroxide, literally rip electrons off molecules to destroy the structure of the pathogen. All of this to say that using a disinfectant to inactivate droplets on surfaces seems like a good way to prevent COVID-19 transmission.

With this context, we can look at the Four C’s of Disinfectants (Chemistry, Concentration, Contact Time, and Coverage) and why they’re important. When we talk about the first three, Chemistry, Concentration, and Contact Time, we really mean 1) what, 2) how much, and 3) how long it takes kill a specific pathogen. For example, the active ingredient in Clorox Healthcare Germicidal Bleach Wipes is 0.55% sodium hypochlorite and it claims a 3-minute contact time against C. difficile spores. In order to go to market, all disinfectants have to submit data to the EPA proving these claims. To be classified as a sanitizer, for instance, the requirement is usually conducting an AOAC- or ASTM-standard test demonstrating a minimum 3-log reduction (e.g. 99.9% reduction, 4-log would be 99.99%, and so on) within 10 minutes on a couple of pathogens. Specifically in the context of COVID-19, we can look at a recent paper that compiled data on the efficacy of disinfectants against enveloped viruses. Sodium hypochlorite at a concentration of 0.5% was able to achieve a >3.0-log reduction in human coronavirus after 1 minute, whereas a 0.06% sodium hypochlorite solution was only able to achieve a 0.4-log reduction in transmissible gastroenteritis virus after the same time period, suggesting that a longer Contact Time than 1 minute is needed for a more diluted bleach solution to effectively kill enveloped viruses or that stronger concentrations should be used in practice.

And this is the key point – all the disinfectants you see on the EPA’s disinfectant list against COVID-19 have varying concentrations of active ingredients that require a different amount of time to be effective [FN1]. So if we go into the database, we’ll see that Micro-kill Bleach Wipes have a 30 second contact time, Sani-Cloth Bleach Wipes have a 1 minute contact time, and Cavicide Bleach has a 3 minute contact time, even though they’re all sodium hypochlorite. You’ll also notice that many of the quaternary ammonium (“quat”) disinfectants (which is the active ingredient in household disinfectants like Lysol and what the media means when they say “alcohol” because quats are dissolved in alcohol) tend to have longer contact times at the 10 minute mark. As discussed above, it’s generally because alcohol breaks down the membrane by bonding and then the quats go in and denature proteins whereas bleach is ripping the virus apart more rapidly via oxidation. One of our gripes with all of the news articles saying that bleach is overkill and that alcohol is sufficient is that they completely neglect the Contact Time. Yes, alcohol can be effective, but often only if you’re letting it sit on the surface undisturbed for 10 minutes, in which time the alcohol could evaporate and you may need to reapply. But who’s actually sitting there with a timer for 10 minutes and making sure the surface stays wet for that time? For the record, this post is NOT meant to incite fear or to say that your standard quat/alcohol disinfectants can’t be effective (you’ll notice some bleach products have 10 minute contact times and some quat disinfectants are 3 minutes [FN2]) but the main message here is to help you understand that effectively disinfecting surfaces requires following a process and not just buying a product. It’s like that saying: it’s how you use it that matters.

Finally, there’s Coverage, which is pretty intuitive and ties everything back to the importance of process – cover every part of the surface and make sure the surface is covered for the correct Contact Time. Of course, this can be difficult when you’re dealing with large surface areas and using a transparent disinfectant, so just try your best to be thorough. It’s worth noting that many of the surfaces you tend to disinfect are waterproof, and when you put a liquid on a waterproof surface, it beads up. If beading occurs, you’re physically unable to achieve the contact time on every part of that surface. The good news is that more disinfectant manufacturers have been addressing this problem by adding surfactants which lower the surface tension of the liquid to allow it to spread out and cover waterproof surfaces. If you spray or wipe down a dark-colored surface, you should be able to see if your disinfectant is forming beads or not.

Normally, this is the part where we pitch you on how Kinnos has developed our Highlight® color additive to solve the Coverage and Contact Time problem, but the intent of this post is to be informational rather than promotional, so just take a look at our website if you’re interested. We hope that this post will help people use disinfectants more effectively, and that we can all work more well-informed to protect ourselves and our loved ones.


Footnote 1: You might be asking how the EPA has approved all of these disinfectants given that no one has actually been able to run tests specifically against COVID-19, and the answer is that the EPA allows disinfectants to use efficacy against the “most resistant representative virus” to claim efficacy on weaker ones. So if you have approval for a more robust non-enveloped virus, then the assumption is that you can easily kill an enveloped one. That’s why the database tells you to follow the instructions for killing things like canine parvovirus, which is a non-enveloped virus.

Footnote 2: One of the secrets of the disinfection world is that specific products are marketed for specific use cases. For example, most hospitals use bleach to kill C. difficile spores, which generally has a contact time of 3-4 minutes, and they’ll slap that number onto their marketing materials. So even if that bleach product can kill a virus in 1 minute, sometimes the manufacturer will just use a 3 minute contact time (or longer) because they know they can easily pass the required AOAC- or ASTM-standard test at that time point and they’re marketing 3 minutes already anyway. To an extent, this is why some of the bleach products may have 10 minute contact times on their EPA labels even though it’s generally known that bleach easily destroys enveloped viruses. Even so, always better to follow the instructions for Contact Time on the label of the disinfectant.

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