Norovirus, aka Norwalk, is in the news again. It’s sometimes called “stomach flu” but has nothing to do with any influenza virus. It does, however, deliver some nasty symptoms above and beyond your standard winter cold. There are no vaccines or antibiotics that can prevent or relieve symptoms but you can reduce your chances of catching it.
Low Tech Works on Norovirus
Like any virus, you cannot treat norovirus with antibiotics and there is no vaccine. You can get infected by direct contact with other people , doorknobs, laundry, food and possibly even by breathing it in. Fortunately, simple chlorine bleach, if used correctly, can be effective in stopping the norovirus.
1000 or 5000ppm; Which?
Regular bleach can do routine sanitizing of bacteria such as E. coli at the relatively low concentration of 50-200ppm. Disinfection of most viruses require levels in the 500-800ppm range. So, why does the CDC (1) recommend 1000-5000ppm for norovirus?
1000ppm chlorine bleach sprayed on surfaces such as doorknobs, handrails, sinks or countertops, is enough to stop bare norovirus. The problem is that Norwalk virus mixed in with vomit and diarrhea remains active even after a floor has been mopped “clean”. Bleach is taken up by any organic matter and since viruses are very small most of the bleach is absorbed by the unseen vomit/diarrhea. The 5000ppm insures that the virus is exposed to something close to 1000ppm.
Preparing Bleach for Sprayers
The CDC (1) instructions for 1000–5000 ppm say to use 5–25 tablespoons of household bleach [5.25%] per US gallon of water. In metric this is ~75 to 375ml per 4L.
The higher strength and volume of bleach mixture is really intended for hospitals and other healthcare facilities which have to deal with worst case scenarios. Daycare or nursing homes may only need to prepare enough for small spray bottles. Let’s assume that just a cup/250ml is required.
If you want to do different concentrations or volumes, you can use our Sanitizer Dilution Calculator. It works in metric units but we list nearest American equivalents as well.
Which Test Strip to Use for Norwalk?
Health and safety inspectors will generally insist you test your solutions for dilution accuracy. This is because it is possible to make mistakes and it also adds a further check in case your bleach strength isn’t at the most common level of 5.25%.
We recommend our 0-10,000 (10K) chlorine test strip for this. The color chart has markings for 1000, 2500 & 5000ppm so this one strip can be used for all the concentrations mentioned above.