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Home / Health / Covid-19 aerosol transmission: a room, a bar, and a classroom: how the coronavirus spreads through the air | Society

Covid-19 aerosol transmission: a room, a bar, and a classroom: how the coronavirus spreads through the air | Society



The coronavirus spreads through the air, especially in indoor spaces. Although it is not as contagious as measles, scientists now openly acknowledge the role played by the spread of aerosols. Aerosols are tiny infectious particles exhaled by an infected person, still suspended in the indoor environment. How does the gearbox work? And, more importantly, how do we stop it?


These are breathing droplets with a diameter of less than 100 microns Can stay suspended in the air for hours

Each droplet releases 1,200 aerosols

These are particles larger than 300 microns, due to the influence of airflow, Fell to the ground in a few seconds

These are breathing droplets with a diameter of less than 100 microns Can stay suspended in the air for hours

Each droplet releases 1,200 aerosols

These are particles larger than 300 microns, due to the influence of airflow, Fell to the ground in a few seconds

These are breathing droplets with a diameter of less than 100 microns Can stay suspended in the air for hours

Each droplet releases 1,200 aerosols

These are particles larger than 300 microns, due to the influence of airflow, Fell to the ground in a few seconds

These are breathing droplets with a diameter of less than 100 microns Can stay suspended in the air for hours

These are particles larger than 300 microns, due to the influence of airflow, Fell to the ground in a few seconds

Each droplet releases 1,200 aerosols

These are breathing droplets with a diameter of less than 100 microns Can stay suspended in the air for hours

These are particles larger than 300 microns, due to the influence of airflow, Fell to the ground in a few seconds

Each droplet releases 1,200 aerosols

At present, health authorities recognize three types of coronavirus transmission media: small droplets produced when talking or coughing. These small droplets will eventually fall into the eyes, mouths or noses of nearby people; although the US Centers for Disease Control and Prevention ( CDC) pointed out that this is the least likely way to be infected with the virus, but the contaminated surface (smoke) still exists, but the observations of the European Center for Disease Control and Prevention (ECDC) support this conclusion. A single case of Covid-19 caused by iron limestone was observed. Finally, it is spread through aerosols – invisible infectious particles exhaled by the infected person are inhaled, and once they leave the mouth, they behave like smoke. Without ventilation, the aerosol will be suspended in the air and become denser over time.

Without ventilation, the aerosol is still suspended in the air, and its concentration becomes higher and higher as time passes.

Breathe, talk and yell

At the beginning of a pandemic, people believed that the large droplets emitted when coughing or sneezing was the main medium of transmission. But we now know that yelling in poorly ventilated rooms for long periods of time also increases the risk of infection. This is because speaking loudly will release 50 times more virus particles than when we are not speaking at all. If these aerosols are not diffused through ventilation, they will become more and more concentrated, thereby increasing the risk of infection. Scientists have shown that these particles (which we also release into the atmosphere when we simply breathe and can escape from improperly worn masks) can infect people who stay within a five-meter radius of an infected person for more than a few minutes, depending on time The length and nature of interaction. In the following example, we outline which conditions increase the risk of infection in this situation.


each Orange dots Represents one Breath dose

Infectable particles Someone inhales

We issue 10 times Number of particles Speak better than us when silent

We issue 50 times Number of particles Yelling than when silent

In the worst case scenario-shouting or singing in a closed space for an hour-Covid-19 people will be released 1,500 infectious dose.

each Orange dots Represents one Breath dose

Infectable particles Someone inhales

We issue 50 times Number of particles Yelling than when silent

We issue 10 times Number of particles Speak better than us when silent

In the worst case-shouting or singing in a closed space for an hour-the people of Covid-19 will be released 1500 infectious dose.

each Orange dots Represents one Respirable particle dose

infection Someone inhales

We issue 10 times Number of particles Speak better than us when silent

We issue 50 times Number of particles Yelling than when silent

In the worst case scenario-shouting or singing in a closed space for an hour-Covid-19 people will be released 1,500 infectious dose.

In the spring, health authorities failed to focus on aerosol transmission, but recent scientific publications have forced the World Health Organization (WHO) and CDC to recognize this.Prestigious article science The magazine found that there is “overwhelming evidence” that airborne transmission is the “main transmission route” of the coronavirus, and the CDC now states that “under certain conditions, they seem to infect other people over six feet.” [two meters] far. These transmissions occur in enclosed spaces with insufficient ventilation. Sometimes, the infected person has shortness of breath while singing or exercising. “

Bar or restaurant

Coronavirus outbreaks at social events, events, and bars and restaurants account for a large proportion. Moreover, they are the most explosive: an epidemic in a nightclub will infect an average of 27 people, compared to only 6 people at a family gathering-as shown in the first picture. One of the most popular outbreaks occurred in a club in the southern Spanish city of Cordoba, and 73 people tested positive overnight. Scientists also recently analyzed an outbreak in a bar in Vietnam where 12 customers were infected with the virus.

school

Schools account for only 6% of the coronavirus outbreaks recorded by the Spanish health department. The motivation for aerosol transmission in the classroom depends entirely on whether the infected person (zero patient) is a student or a teacher. The teacher’s words are far more than the students, their voices have to be heard by people, which will expel potentially infectious particles. In contrast, infected students only talk occasionally. According to the guidelines of the Spanish National Research Council (CSIC), the Spanish government recommends ventilating classrooms (even if it may cause discomfort in colder months) or using ventilation equipment.

In order to calculate the possibility of human-to-human transmission in a “high-risk” situation, we used the Covid airborne transmission estimator developed by a group of scientists led by Professor José Luis Jiménez of the University of Colorado. This tool aims to emphasize the importance of measures to prevent the spread of aerosols. The calculation is not exhaustive, nor does it cover all the countless variables that may affect transmission, but it aims to show how to reduce the risk of infection by changing the conditions we do control.

During the simulation, the subjects kept the recommended safe distance, eliminating the risk of spreading through droplets. However, if all possible precautions are not taken at the same time, they will still be infected: correct ventilation, shorten contact time, reduce the number of participants and wear masks. Regardless of the environment, the ideal scene is outdoors, where infectious particles will spread rapidly. If a safe distance from the infected person cannot be maintained, the possibility of transmission will increase exponentially because of the risk of droplet (not just aerosol) transmission. To make matters worse, even with ventilation equipment, if two people are together, the aerosol cannot be diffused.

The calculations shown in the three different cases are based on studies of how aerosol transmission occurs and use actual outbreaks that have been analyzed in detail. A very relevant case of understanding the dynamics of indoor communication is the choir rehearsal in Washington State, USA in March. Only 61 of the 120 members of the choir participated in the rehearsal and worked hard to maintain a safe distance and hygiene measures. But they don’t know that they are in the most risky scenario: long time no mask, ventilation, singing and sharing space. Within two and a half hours, only one infected person infected 53 people. Some of the infected are located 14 meters away, so only aerosols can explain the spread. Two of those infected with the virus died.


Coronavirus cases

Rehearsal for 13-15 days

A kind Single infected person The person sitting in the front row infected other people.

Coronavirus cases

Rehearsal for 13-15 days

A kind Single infected person The person sitting in the front row infected other people.

Coronavirus cases

Rehearsal for 13-15 days

A kind Single infected person The person sitting in the front row infected other people.

After carefully studying the outbreak, scientists were able to calculate the extent to which the risk could be mitigated if measures were taken to prevent airborne transmission. For example, if you wear a mask, the risk will be halved, and only 44% will be affected instead of 87%. If the rehearsal is conducted in a short ventilated space, only two singers will be infected. These super-spread situations seem to be increasingly critical to the development and spread of the pandemic, which means that having the tools to prevent the large-scale spread of such events is the key to controlling the pandemic.

method: We calculated the risk of Covid-19 infection using a tool developed by José Luis Jiménez, an atmospheric chemist at the University of Colorado and an expert in air chemistry and kinetics. Scientists all over the world have evaluated the estimator, which estimates the importance of different measurable factors in infection scenarios based on published methods and data. However, the accuracy of the estimator is limited because it relies on numbers that are still uncertain, such as numbers describing how many infectious viruses are distributed by an infected person. The estimator assumes that people have practiced the two-meter social distancing rule, and no one is immune. Our calculations are based on the general population’s default values, which include various masks (surgery and clothing) and louder sounds, which increase the amount of aerosol emitted.

‘S video Luis Almodóvar.

English version Heather Galloway.


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