This post goes along with the JIFFI post about surgical hand hygiene from last year, since it’s about a low-cost way of keeping the surgical environment clean. For a lot of people, this will be old news, but for anyone who hasn’t used calcium hypochlorite to disinfect in their clinic, or who is wondering about the research behind this disinfectant and its preparation, read on–
Origin story
Back in the fall of 2010, in the days of Trifectant, before accelerated hydrogen peroxide took the shelter disinfection world by storm, my friend Brenda was raving about a kennel cleaner called Wysiwash. The active ingredient is calcium hypochlorite, and the product is sold as a hose-end sprayer for kennel disinfection. There was a lot to be excited about: it’s cheap and effective against most of the pathogens we’re worried about in veterinary care, it’s much less irritating than bleach, and it doesn’t need to be rinsed away.
But I have a MASH mobile spay neuter clinic: I don’t have kennels or a hose, and I only need a gallon or two of disinfectant every day. How could I use this product? Sure, I could put a hose-end sprayer on a hose at home and fill a jug, but how would that work in the winter when the hoses are frozen solid? I decided there had to be some other way to purchase and mix calcium hypochlorite.
Researching an alternative
After spending some time on Google, I found that one of the most easily available forms of calcium hypochlorite is swimming pool shock. But how much to use? And which type?
Fortunately, Wysiwash and many of the pool shock suppliers also provided online copies of MSDS (now SDS) sheets listing the chemical composition of each product. After downloading a bunch of these MSDS sheets, I was able to find Turbo Shock, a pool shock product with the same chemical composition– the same components, in the same proportions– as Wysiwash. Turbo Shock is supplied as a white granular powder and can be purchased in a 1-pound bag.
Next I had to figure out how much to use. For that, I turned to the technical information page on the Wysiwash site and found this paper describing how to make a 2x solution of Wysiwash in the lab. Armed with that information and the density of the pool shock (also from the MSDS), I was able to make the calculation that you would need just over 1/16 teaspoon of Turbo Shock per gallon of water to make the same strength solution as the hose-end sprayer. For practical reasons (the smallest plastic measuring spoon I can find is 1/8 tsp, and metal measuring spoons rust almost immediately when used in pool shock), I end up using a 2x concentration, mixing 1/8 tsp per gallon. At this rate, it takes me a few years to go through just one bag of Turbo Shock.
I started using this solution that fall, and by spring of 2011, I mentioned Turbo Shock using in a conference presentation at the SNIP Summit in Asheville. After that presentation, other spay neuter and shelter vets have started using calcium hypochlorite solution made from pool shock, especially for disinfecting endotracheal tubes, masks, and pulse oximeter probes between patients, and in some cases for disinfecting animal contact surfaces such as scales and tables.
But wait…!
So I know what y’all are thinking: “What about that 2015 article by Dr. Karen Moriello showing that calcium hypochlorite was ineffective against ringworm?” I read this one too, but I’m not quite ready to throw the baby out with the pool water.
In this study, in order to obtain the calcium hypochlorite solution, a Wysiwash hose-end sprayer was used and the solution was collected midstream after the hose had run for 3 minutes. One of the downsides of a hose-end sprayer is that you have to take it on faith that the correct amount of disinfectant is being dispensed at any given moment. This made me wonder– what if the solution that was being dispensed from that hose was not as concentrated as it should have been? What if there was something wrong with the sprayer and there wasn’t any calcium hypochlorite in it at all? The strengths of the various solutions used in the study were never verified; for the study design, this was appropriate (after all, she was using kennel disinfectants according to label and assessing their effectiveness), but it doesn’t tell me for sure that a solution of calcium hypochlorite is ineffective against ringworm fungus.
So if any of you who are reading this are students, interns, or residents and you’re looking for a project, I would love to see the calcium hypochlorite portion of this study replicated with a known or verified concentration of the chemical. This could be done by testing the chlorine content of the solution, which should be between 60-70 ppm for a 1x solution or about 120 ppm for a 2x solution, and could be tested with commercial chlorine test strips. Why not test both strengths and let us all know how it turns out?
Pro tips
As I mentioned above, calcium hypochlorite powder can corrode metal when in prolonged contact (I have had no problem with the mixed solution causing damage when disinfecting metal surfaces, though). Avoid using a metal measuring spoon. I’ve also been told that one clinic that stored a bag of pool shock under their sink found that just the fumes from the bag of pool shock corroded the metal pipes under the sink– so be careful and store away from metal. Plastic measuring spoons and plastic storage containers seem to hold up well.
Since it takes me a long time (years) to go through a 1-pound bag of Turbo Shock, I dispense the powder into a labeled pill vial to carry with me to clinics. I re-seal the pool shock bag by rolling down the edge and using a rubber band to secure it (the metal clip in the photo attached to this blog post? Completely rusted now).
It’s also probably obvious (if you think about swimming pools, or chlorine bleach), but calcium hypochlorite is not a detergent or a cleaner: it’s a disinfectant, but it won’t do any more than water would do to clean slimy, messy, dirty objects. For anything that’s dirty, slimy, etc (including endotracheal tubes), clean first (soap and water!), then disinfect.