Researchers in Finland have released a chilling computer simulation that shows how the coronavirus can spread in places like supermarkets when droplets from a single cough remain in the air for several minutes — even migrating across multiple aisles.
Aalto University, the Finnish Meteorological Institute, the VTT Technical Research Centre of Finland and the University of Helsinki studied how extremely small airborne aerosol particles emitted from the respiratory tract when someone coughs, sneezes or even talks are transported in the air. Such particles can carry pathogens such as the coronavirus.
The four institutions each independently carried out modelling of a scenario where a person coughs in an aisle between shelves, like those found in grocery stores.
The researchers obtained the same preliminary result: The aerosol cloud spreads outside the immediate vicinity of the coughing person and dilutes in the process, but this can take up to several minutes, they said.
“Someone infected by the coronavirus can cough and walk away, but then leave behind extremely small aerosol particles carrying the coronavirus,” said Aalto University Assistant Professor Ville Vuorinen. “These particles could then end up in the respiratory tract of others in the vicinity.”
Jussi Sane, chief specialist at the Finnish Institute for Health and Welfare, said the preliminary results of the modelling highlight the importance of the institute’s recommendations — recommendations similar to those of the Massachusetts Department of Public Health and the U.S. Centers for Disease Control and Prevention.
“The Finnish Institute for Health and Welfare recommends that you stay at home if you are unwell and that you maintain physical distance with everyone,” Sane said. “The instructions also include coughing into your sleeve or a tissue and taking care of good hand hygiene.”
The researchers modeled the airborne movement of aerosol particles smaller than 20 micrometer — one micrometer is 0.000039 of an inch. For a dry cough, a typical symptom of the coronavirus, the particle size is usually less than 15 micrometers, they said. Extremely small particles of this size do not sink on the floor, the researchers said, but instead move along in the air currents or remain floating in the same place.
The researchers simulated the airborne transport and preservation of droplets leaving the respiratory tract by using a “supercomputer” capable of producing results in days rather than years, and a 3D visualization of the results was then carried out.
