Study analyzes the contagious capacity of a single drop of saliva

A study by the UPV/EHU University of the Basque Country has shown that the safety distance of two meters can be reasonable to prevent Covid-19 infection.

According to a study published in the journal Nature, temperature, humidity and droplet size are the factors to consider in the behavior of a saliva drop. The research was conducted in the Department of Nuclear Technology and Fluid Mechanics of the UPV/EHU and can help make decisions in a pandemic situation like the one with Covid-19.

The transmission capacity of a virus is one of the most important factors to consider in infectious disease research. The vast majority of viruses are transmitted orally. When a person coughs, speaks, or sneezes, he or she exhales some highly infectious particles or saliva droplets into the environment. The evaporation of the droplets depends on several factors in the droplet, and so disease transmission varies. “The aim of this work was to study the behavior of a salivary particle exposed to different environmental features of a social environment through computational simulations,” explained Ainara Ugarte-Anero and Unai Fernández-Gamiz, researchers from the UPV/EHUs. Department of Nuclear Engineering and Fluid Mechanics.

To study how a saliva drop behaves in air, they created a computational simulation based on Computational Fluid Dynamics (CFD) that examines the state of a saliva drop as it moves through the air when a person talks, coughs or sneezes. “This simulation was performed in a controlled, simplified environment. In other words, instead of analyzing a general sneeze with a number of particles, we focused on the study of a single particle in a closed environment. To do this, we allowed droplets of between 0 and 100 microns to fall from a height of about 1.6 meters – about the distance of a human mouth – and took into account the effects of temperature, humidity and droplet size,” explains Unai Fernández-Gamiz .

“The results show,” says Ainara Ugarte, “that ambient temperature and relative humidity are parameters that significantly influence the evaporation process. The evaporation time is usually longer when the ambient temperature is lower. And particles with smaller diameters will evaporate quickly, while those with larger diameters take longer”. “Some large particles, about 100 microns in size, can stay in the environment for 60-70 seconds and are basically transported over a longer distance, so for example, a person could sneeze in an elevator and then exit the elevator while the particles can Hence the importance of the safety distance of two meters in closed environments in the case of Covid-19. According to what has been researched, it seems that this distance may be reasonable to prevent further infections in the case of Covid -19″, said the lead author of the article. Moisture must also be added to this. “In a humid environment, evaporation takes place more slowly, so the risk of contamination is higher because the particles stay in the air longer,” Ugarte added.

The researchers from the Department of Nuclear Technology and Fluid Mechanics of the UPV/EHU agree that “this is a fundamental study, but at the same time an essential one, because it will allow us to deal with much more complex situations in the future. Until So far, by studying the dynamics of a single drop, we have explored the foundations of a building”.


University of the Basque Country

Reference magazine:

Ugarte-Anero, A., et al. (2022) Computational characterization of the behavior of a saliva drop in a social setting. Scientific Reports.

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