Disinfectants and hand sanitisers: a new test of efficacy against viruses

In light of the recent appearance of a novel coronavirus disease, COVID-19, into southern China, the authors adapted the Spearman-Kärber^1,2 tissue culture infectious dose₅₀ (TCID₅₀) test method in order to test the efficacy of hand sanitisers and disinfectants over time on surfaces and on the skin.

It is important when using any disinfection chemistry both to know what it kills and for how long. It is clear from studies of bacterial contamination on hands and surfaces that the longer disinfectants and sanitisers remain active, the more effective they are at reducing the potential for cross-infection. As the coronavirus responsible for COVID-19 almost certainly is spread predominantly by droplets, disinfection of surfaces and sanitation of hands become of even greater importance to reducing its spread.

There are now two main categories of disinfectants and sanitisers commercially available,^3–5 yet most test methodologies are only appropriate for one of them. It is relatively easy to differentiate between these two categories. The non-persistent chemistries (wet in use) and the persistent chemistries (dry in use) have significantly different instructions for use. The main practical difference is the longevity of antimicrobial activity. Once applied, how long does antimicrobial activity continue? In the case of alcohol, this may be as little as 35–60 seconds,⁶ and for chlorhexidine gluconate (CHG), up to around four hours on skin. On surfaces, it is a little more difficult to be accurate about the persistence of activity, as this will depend on concentration and the amount of fluid used, environmental temperature and humidity.⁷