We have been told the importance of washing our hands to prevent the spread of viruses. But how easily do viruses spread? An experiment done by the Japanese public broadcast TV station NHK looked at what happens in public places where people congregate, such as at a restaurant buffet. They put some invisible fluorescent paint on the hand of one person and after 30 minutes used black light to find out where it had ended up.

To begin with, one guest of 10 at a restaurant buffet is shown with the substance on his hands meant as a stand-in for the coronavirus. Over the course of a typical dining period, the rest of the guests behave in predictable fashion, selecting utensils from serving stations, enjoying their food, checking their phones and so on.

At the end of the experiment the backlight is turned on and the substance is revealed to be smeared everywhere: plates, foodstuff, utensils and even all over some of the guests’ faces.

A second experiment in the same environment showed the benefits of improved hygiene techniques. The “infected” person and the other diners washed their hands before and throughout the meal, and utensils and other implements were cleaned and replaced more frequently.

“What the video demonstrated, is that it will spread to surfaces and to people very efficiently,” John Nicholls, a clinical professor in pathology at Hong Kong University, told CNN. “I think it really highlights the need of what people have been saying about hand hygiene to stop the spread of disease.”

Here is the video of the experiment.

The rate of spread would depend upon how much of the stuff you start with, how much the stuff ‘sticks’ to a person, and how much gets transferred to whatever they touch. I don’t know if the SARS-CoV-2 virus gets spread in a manner similar to fluorescent paint but the test is still illustrative of how much we come into contact with things and later are in contact with other people and things.