# Simulation shows the chance of transmission of Covid-19 in several cases

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The Spanish newspaper El Pas published an article detailing the risk of transmission of the Sars-Cov-2 coronavirus, responsible for Covid-19, in various scenarios in everyday life. The simulations, which include scenarios such as a meeting between friends at home, a classroom and a visit to a bar or restaurant, were based on a tool developed by Professor Jos Luis Jimnez, from the University of Colorado, USA.

The tool was created to highlight the effectiveness and importance of measures that prevent the spread of aerosols, particles emitted when we speak, cough or sneeze, which are the main form of transmission of the disease.

According to the newspaper, the calculations are not exhaustive, nor do they cover all the variables that can affect transmission, but serve to illustrate how the risk of contagion can be reduced by changing conditions over which we have control.

## Meeting with friends

A good example is a meeting between six friends in a closed room, for four hours and without anyone wearing masks. In this scenario, one person will infect all five others, even if a safe distance is maintained between them.

If masks are used, four people are at risk of being infected. This shows that alone, the accessory is not able to prevent an infection if the exposure to the virus is prolonged. But if all people wear masks, the duration of the meeting is reduced to two hours and the space is ventilated, the risk of contagion of less than one person.

Visualization of the effectiveness of the use of masks to contain respiratory droplets that can spread Covid-19. Photo: Atlantic University of Florida

## Visit to a bar

Another scenario is a bar, with a capacity reduced by 50% and occupied by 18 people: 15 customers and three employees. If the windows are closed and there is no mechanical ventilation of the environment, 14 people will be infected after four hours.

With just the use of masks, the number drops to eight new cases. But if the place is ventilated, people wear masks and the exposure time is limited to two hours, the risk that only one person will be infected.

## In the classroom

The ultimate simulation of a classroom. The risk of new cases is greater if the teacher is ill, since he speaks constantly and often needs to raise his voice to be heard, which increases the emission of aerosols. In this case, in a closed room with 24 students and no measures to limit contamination, there is a risk that 12 students will be infected.

If everyone wears masks, the number of possible infections drops to five. But if the environment is ventilated and the duration of the lesson is limited to one hour, so that the air can be renewed completely, it drops to just a new case.

## Lethal encounter

The calculations for the simulation were based on a study of how aerosol transmission occurs, using as a model real outbreaks of other epidemics that have been studied in detail.
One of them was a rehearsal of a church choir in Washington State, USA, in March of this year. Only 61 of the 120 members of the choir were present, and efforts were made to maintain a safe distance between them and to follow hygiene measures.

However, the participants did not know that they were in a high-risk situation: without masks, in a closed environment without ventilation and singing and sharing the space for an extended time.

In just two and a half hours, only one person infected 53 others. Some of them were more than 14 meters away, which can only be explained by aerosol transmission. Two of the infected people died.

Source: El Pas