Evaluating current sanitation methods

The COVID-19 outbreak has seen a surge in products claiming to be ‘effective at killing the Sars-Cov-2 virus’. However, many common disinfectant solutions making this bold claim may not be as effective as people are led to believe. George Duncan, of water sanitation specialist Scientific Sanitation Solutions (SSS), addresses some of the misconceptions and explains what ‘killing 99.9% of pathogens’ actually means.

There are a vast number of products currently claiming to protect against COVID-19, most of the time to 99.9%. Although this sounds impressive, there are several issues to address with these claims. Firstly, the 99.9% efficacy (also known as log-3 efficacy) is not instant. Many products require it be left to work on a surface for a period of time before then wiping clean, giving whatever pathogens are on that surface an opportunity to continue multiplying. Secondly, many of the commonly-used disinfectants are alcoholbased, which presents dangers to skin and eyes, especially on the hands due to frequent washing and use of alcohol-based gels without moisturiser

The effectiveness of a disinfectant is measured by the relative number of microbes eliminated by it from the surface. Solutions at log-3 effectiveness, or 99.9%, which most cleaners state, remove one in 1,000 microbes; log-4 removes one in 10,000 and so on, up to log-6, which clears 1 in 1,000,000 (effectively a sterile environment).¹ If we give an example of 100 million pathogens or bacteria, a solution at log-3 efficiency 99.9% would clear all but 100,000 pathogens/bacteria, but a solution with log-6, efficiency 99.9999%, would leave only 100 parts in 100 million, which is effectively sterile. The efficacy of frequently-used disinfectants tends to be towards the lower half of the chart. However, the solution could lie in the way water is treated and sanitised.