what to pay attention to to avoid contagion

As is known, closed environments are ideal for the proliferation of SARS-COV-2, But by putting some simple measures into practice, it is still possible to minimize the risk of contagion. If in the first phase of the pandemic the importance of hand hygiene was emphasized, with the passage of time it became evident that most infections occurred in another way: after close and direct contact with a person positive for the virus but also through aerosols: tiny particles of less than 100 μm that can travel up to two meters, accumulate in the air and be inhaled.

The role of aerosols in the transmission of the virus.

Recently, the US CDC (Centers for Disease Control and Prevention) has also recognized the importance of airborne transmission in SARS-COV-2 infection. And so does the European Center for Disease Prevention and Control (ECDC), which however prefer Be more cautious in judging the evidence for this type of contagion as “less robust.” An article published the prestigious journal “Science” instead speaks of “overwhelming evidence” that explains that in a closed space aerosols smaller than 100 µm can accumulate in the air “causing overdiffusion events”.

The Spanish newspaper “El País” I tried to calculate the risk of infection in a closed environment using a calculation model developed by Professor José Luis Jiménez from the University of Colorado. This is not a foolproof method, the newspaper said, but probably accurate enough to understand how the virus “works” indoors, even where the two meter safety distance is respected.

“El País” shows three very common situations in which contagion can occur: a meeting with friends / family in the living room; a lunch in a bar or restaurant and a class lesson.

Thus, the virus spreads among friends and family.

Scenario 1: “El País” assumes that there are 6 people in our living room (dimensions are not known), one of whom is infected with SARS-COV-2. In such a case, regardless of the safe distance, without masks and adequate ventilation, those infected could transmit the virus to everyone else present within 4 hours. If everyone wore a mask, infections would be reduced from 5 to 4, but contagion would continue to exist because with very long exposure not even protective devices are able to stop the virus. In such cases, just ventilating the environment and reducing the duration of exposure by half (from 4 hours to 2 hours) significantly reduces the risk to less than one infected person. However, as long as you wear personal protective equipment. According to “El País” in Spain, 31% of contagion cases are a direct consequence of this type of situation.

(Infographic: EL Pais)

Contagion at the bar or restaurant

Scenario 2: In a bar there are 15 people who consume and three employees. The doors are closed and there is no mechanical ventilation. Well, in the worst case, without taking any security measures after four hours, all 14 clients would be infected with the virus. If everyone wore protective equipment, infections would be reduced to 8. With masks, adequate ventilation and an exposure time reduced by half (4 to 2 hours), the chances of contagion are drastically reduced: the virus could only infect one person .

[1/7] Covid is spread through the air, especially indoors, and scientists already openly acknowledge the role of aerosols in the pandemic. In EL PAÍS we have recreated three common environments to see how these infections work and, above all, how to avoid them 👇 pic.twitter.com/Z2esKOPch1

– THE COUNTRY (@el_pais) October 25, 2020

In a classroom

Scenario 3: a classroom with 24 students. The most dangerous situation occurs in an unventilated classroom where the infected person is the teacher. In such a case, without anti-virus security measures, 2 hours is enough to infect 12 people. Also in this case the use of masks drastically reduces the risk of contagion (from 12 to 5 infected people) but does not eliminate it completely. By cutting the exposure time in half (from 2 hours to 1 hour) and properly ventilating the classroom, the virus could infect a single person. “El País” specifies that unlike what one might think, in real situations the distribution of infections is random, since without ventilation “the aerosols accumulate and are distributed throughout the room.”

Airborne transmission of coronavirus

But why is he airborne? “El País” explains that today, contrary to what happened in the past, it is not believed that the risk of contagion exists only if we are faced with a person who coughs or sneezes. Sharing a closed environment with a person who is talking, yelling, or singing for a long time also amplifies the risks of contracting SARS-VOC-2. In one hour, a screaming person emits 50 times more infectious aerosols in one hour than in a situation of silence.

The importance of ventilating classrooms and rooms

Another study by a group of physics researchers from the University of New Mexico showed that even in the classroom, ventilation is essential to contain SARS-COV-2 infection. According to scholars, 1 micrometer-size particles can be transmitted even at a distance of almost 2.5 meters, but good ventilation could disperse 70% of them.

Infographic credit: “El País”

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