How viruses can spread indoors - A group of researchers from Finland showed through simulation

A group of researchers from Finland showed through simulation how coughing can spread viruses in the air in an indoor environment like a supermarket.

The joint study of Aalto University, Finnish Meteorological Institute, VTT Technical Research Centre of Finland and University of Helsinki showed that extremely small airborne aerosol particles emitted when coughing, sneezing or even talking are transported in the air. Such particles can carry pathogens such as coronaviruses.

The researchers created a simulation where a person coughs in an aisle between shelves, like those found in grocery stores, taking ventilation into consideration. The preliminary results revealed that “aerosol particles carrying the virus can remain in the air longer than was originally thought.”

The aerosol cloud spreads outside the immediate vicinity of the coughing person and dilutes in the process, but that can take up to several minutes, the study found.

"Someone infected by the coronavirus, can cough and walk away, but then leave behind extremely small aerosol particles carrying the coronavirus. These particles could then end up in the respiratory tract of others in the vicinity," explains Aalto University Assistant Professor Ville Vuorinen.

In line with these findings, the researchers said it is important to avoid busy public indoor spaces as this would mean “reducing the risk of droplet infection, which remains the main path of transmission for coronavirus.”

"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. The instructions also include coughing into your sleeve or a tissue and taking care of good hand hygiene,” said Jussi Sane, Chief Specialist at the Finnish Institute for Health and Welfare.

The researchers modeled the airborne movement of aerosol particles smaller than 20 micrometers. For a dry cough, which is a typical symptom of the current coronavirus, the particle size is typically less than 15 micrometres. The study showed that small particles of this size do not sink to the floor, but instead, move along in the air currents or remain floating in the same place.

Studies of influenza A have confirmed that the influenza A virus can be found in the smallest particles, which measure less than 5 micrometres.

“Based on the modelling of the consortium, it is not yet possible to directly issue new recommendations. However, these results are an important part of the whole, and they should be compared with the data from real-life epidemic studies,” Sane added.