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.
Note: we now use indigoinstruments.com; ignore image references to our original domain, indigo.com.
What Cleaners Kill Norovirus?
How Long Does Norovirus
Live on Surfaces?
Norovirus can survive up to 2 weeks on surfaces such as doorknobs, laundry, and handrails. Disinfection of most viruses require levels in the 500-800ppm range. So, why does the CDC (1) recommend 1000-5000ppm for 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. By preparing a 5000ppm concentration, you insure that the virus is ultimately exposed to something that is at least 1000ppm.
Preparing Bleach for Sprayers
The CDC (1) instructions for 1000–5000 ppm says to use 5–25 tablespoons of household bleach [5.25%] per US gallon of water. In metric, this is ~75 to 375ml per 4L.
Hospitals and other healthcare facilities have to deal with worst-case scenarios so higher strengths and a greater volume of bleach mixture are required. Daycare or nursing homes may only need to prepare enough for small spray bottles, a cup/250ml is usually enough.
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.