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The 4 C's of Disinfectants

If you’ve ever stopped to read the label of your Lysol Wipes at home, the first thing you’d probably learn is that you’ve been disinfecting incorrectly. The label instructs you to wipe the surface until it's visibly wet and to let it remain wet for 10 minutes in order to effectively kill pathogens. It seems infeasible to set a timer for every surface you’ve wiped and then check that it's still wet 10 minutes later, but that’s exactly how disinfection should occur. More often than not, people tend to wipe away the disinfectant with a dry paper towel or the disinfectant evaporates before those 10 minutes are up. While at home the stakes are low, in hospitals and laboratories around the world, this lack of compliance is being made with sometimes deadly consequences.

A huge amount of resources in the healthcare industry are largely prioritized toward making diagnoses and treating illnesses. However, we often forget that many ailments, particularly infectious diseases, are frequently preventable. Part of the problem is that prevention (such as using disinfectants correctly) is difficult. Last month, Kinnos sponsored the Yale-Harvard Symposium and gave a talk at the Connecticut Biosafety Alliance Symposium at Yale University on this topic. We discussed the complexities of disinfectants and it resonated strongly with the biosafety officers attending the conference. To help spread awareness about the transmission of infectious diseases and to build a well-informed community, we're sharing an adapted version of that talk here.

CEO Jason Kang speaks at the Connecticut Biosafety Alliance Symposium. June 2017.

CEO Jason Kang speaks at the Connecticut Biosafety Alliance Symposium. June 2017.

Using a disinfectant properly is surprisingly complex. Although we wish we could take credit for it, Ben Fontes (a globally-recognized biosafety officer at Yale and the most charismatic guy you’ll ever meet) helped us coin the four C’s that are necessary for effectively using a disinfectant:

  1. Chemistry – The chemical that’s responsible for inactivating the pathogens. It could be sodium hypochlorite, quaternary ammonium compounds (quats), hydrogen peroxide, alcohol, and so on.
  2. Concentration – The level at which that chemical is diluted in solution. Maybe it’s 2,000 parts per million maybe it’s a 1:10 dilution.
  3. Contact Time – The amount of time it takes for the disinfectant to sit on a surface before a certain pathogen is inactivated. For instance, 30 seconds for E. coli or 3 minutes for C. difficile spores with bleach.
  4. Coverage – The amount of surface area that the disinfectant is covering after it’s applied. Ideally, this is 100%.

Most organizations only focus on the first two or three C’s. They’ll pick Clorox Healthcare Bleach Germicidal Cleaner (0.65% sodium hypochlorite) or Cavicide (17% alcohol), or we’ve seen hospitals trade in a 4-minute contact time quat wipe for a 3-minute contact time bleach wipe. Organizations rely on the fact that disinfectant manufacturers have gone through the expensive and time-consuming process of getting EPA-registered claims against a broad spectrum of bacteria, viruses, and fungi. However, efficacy in laboratory settings where EPA-standard tests are conducted does not always translate to similar results in practice.

Droplets of disinfectants form gaps in coverage on this waterproof PPE suit.

Droplets of disinfectants form gaps in coverage on this waterproof PPE suit.

First, let’s look at the issue of coverage. Most disinfectants are transparent, making it difficult to confirm complete coverage on treated surfaces. Imagine you're a housekeeper in a large hospital and your job is to disinfect every surface in 20 patient rooms during your shift. Can you really be certain you’ve wiped down every square inch of every countertop, bed rail, toilet, and shower tile in each of these rooms every single day? It becomes even more challenging when surfaces aren’t smooth – if you’re a healthcare worker handling Ebola patients, how can you be sure that every single nook, cranny, and wrinkle of your PPE suit has been disinfected?

An additional problem is that the vast majority of surfaces that you apply a disinfectant on are waterproof. This means that disinfectants without a surfactant will bead up and form droplets, leading to gaps in coverage. We conducted a test where we sprayed a standard 10% bleach solution (with a dye added to help visualize coverage) on a vertical surface with a trigger sprayer and allowed it to sit for 10 minutes. Using a script, we were able to calculate the percentage of surface area covered and found that standard bleach covers less than 1/3 of the surface area as soon as it hits the surface and that the coverage decreases over time as droplets roll down and evaporation occurs.

Bleach sprayed on a vertical waterproof surface exhibits poor coverage that decreases over time.

Bleach sprayed on a vertical waterproof surface exhibits poor coverage that decreases over time.

What makes this poor coverage such a big issue is the contact time. If 2/3 of the surface fails to be covered a few seconds after you apply the disinfectant, then the majority of the surface will not be properly disinfected even if you wait for the correct contact time. You can imagine that this problem is magnified in hot, arid conditions where evaporative effects are even more pronounced and the disinfectant may dry out well before reaching the target contact time.

But what about disinfectants that don’t form droplets? Some disinfectants like Clorox Healthcare Bleach Germicidal Cleaner contain a surfactant, and disinfectant wipes tend not to form as many droplets as sprays. Coverage may be solved, but enforcing compliance with contact time is still a tremendous challenge.

Almost everyone we’ve talked to in the disinfection industry agrees that compliance is an age-old problem. No one is carrying around stopwatches to make sure they’re waiting the correct contact time. When we shadowed housekeepers at large hospitals, we saw instances where they would wipe down a surface with bleach, and take a dry paper towel and wipe off the bleach immediately afterwards. This is because housekeepers are also told that patients don’t like the smell of bleach, the bleach will corrode the surface, or the bleach will leave behind white salt residues when it dries – but clearly the larger issue is that nothing is being killed if they wipe off the bleach too quickly. In other situations, we’ve also seen housekeepers overuse a single bleach wipe for too many surfaces (to the point where there was no more bleach on the wipe) or where they leave the wipe canisters uncapped and they’re using completely dried-out wipes. These instances of non-compliance with contact time are only exacerbated by the fact that many housekeepers have a high turnover rate and are infrequently trained.

Disinfectants have been used in these settings for over 20 years, but the fact that 1 out of every 25 patients will get a healthcare-associated infection means that these disinfectants alone aren’t good enough. The four C’s of disinfectants need to be emphasized.