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Experts constantly warn: Wearing a mask and good ventilation of the space help reduce the spread of the coronavirus. El País gave a unique example, with three daily stages in a house, a bar and a classroom.
The risk of transmission of the coronavirus is higher indoors, but can be reduced by implementing all available measures to combat aerosol contamination. The following is an overview of the possibility of infection in three daily scenarios, depending on the security measures used and the duration of exposure.
room
Six people meet in a house, one of which is infected. Around 31% of the coronavirus outbreaks registered in Spain are caused by such concentrations, mainly among family and friends.
Regardless of keeping safe distances, if the 6 people spend 4 hours together talking loudly, without a mask, in a room without ventilation, the other 5 people will become infected.
If they wear a mask, 4 more people are at risk of infection. Masks alone will not prevent infection if exposure is prolonged.
The risk of contagion is reduced to less than one person if the group uses masks, halves the duration of the concentration and ventilates the space they use.
The coronavirus is spread through the air, especially indoors. Although not as contagious as measles, scientists recognize the role that aerosol transmission plays – tiny transmissible particles that are exhaled by an infected person and remain suspended in the air in an indoor environment. How does the transmission work? And, most importantly, how can we stop it?
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Health authorities currently recognize that there are three “vehicles” to transmit the coronavirus:
1. Small drops that are released when someone speaks or coughs, which can end up in the eyes, mouth or nose of those who are nearby. 2. Contaminated surfaces, although the US Centers for Disease Control and Prevention indicates that this is the least likely way to contract the virus, a finding supported by the observation of the Centers for Disease Control and Prevention. Diseases of which there has not been a single case of coronavirus caused by an infected surface. 3. Transmission by aerosols: inhalation of invisible infectious particles that an infected person exhales as soon as they leave the mouth, a behavior similar to smoking. Without ventilation, the aerosols remain suspended in the air and become more dense as time passes.
How much risk increases with voices
At the beginning of the pandemic, the large droplets that we cough up or sneeze were thought to be the main means of transmission. But now we know that yelling or singing indoors, with insufficient ventilation for a long time, also increases the risk of transmission. This is because loud speech releases 50 times more virus particles than when we don’t speak at all. These aerosols, if not diffused through ventilation, increase more and more, increasing the risk of contamination. Scientists have shown that these particles, which we also release into the atmosphere when we simply breathe and which can escape improperly made masks, can infect people who spend more than a few minutes within a 5 meter radius of an infected person. depending on the length of time and the nature of the interaction.
The following example describes which conditions increase the risk of transmission in this condition.
In the spring, health authorities did not focus on aerosol transmission, but recent scientific studies have forced the WHO and CDC to acknowledge it. An article in the prestigious journal Science found there was “overwhelming evidence” that airborne transmission was an “important route of transmission” for the coronavirus, and the CDC now notes that “under certain conditions, they appear to have infected more than 6 others. These transmissions were made indoors with insufficient ventilation: “Sometimes an infected person breathes with difficulty, for example when singing or exercising.”
Bar or restaurant
The outbreaks appear to be exacerbated during pregnancy and in families, including bars and restaurants, with a significant number of contagious effects on social media. In addition, they are the most explosive: each outbreak of a coronavirus in a nightclub infects an average of 27 people, compared to only 6 during family gatherings, as explained in the first graph. One of these “outbreaks” of coronavirus occurred in a club in Córdoba, Spain, where 73 people tested positive for coronavirus after a night out.
The example of the bar
In this bar, the capacity has been reduced to 50%. There are 15 clients and three staff members. The windows are closed and there is no mechanical ventilation.
In the worst case, if no action is taken, 14 of the clients will be infected after 4 hours.
If the masks are used constantly, the risk of infection is reduced to 8 new cases.
If the rooms are ventilated, something that can be done with a good air conditioning unit, and the time spent in the bar is reduced, there is a risk of infecting a person.
Schools
Schools represent only 6% of the coronavirus outbreaks registered by the Spanish health authorities. The dynamics of aerosol transmission in the classroom changes completely depending on whether the infected person – or the “sick zero” – is a student or a teacher. Teachers speak louder than students and turn up the volume to be heard, which multiplies the expulsion of potentially contagious particles. In comparison, a student speaks only occasionally. In accordance with the instructions of the Higher Council for Scientific Research (CSIS), the Spanish government has recommended that classrooms be ventilated – although this may cause discomfort during the colder months – or that ventilation units be used (a similar request was made in Germany).
The classroom example
The most dangerous scenario is a classroom without ventilation and the teacher – “patient zero” as the infected person.
If you spend two hours in the classroom with an infected teacher, without taking steps to address the amount of aerosols, there is a risk of infecting up to 12 students.
If everyone wears a mask, the number of people who could be infected drops to five. In coronavirus outbreaks, it has been observed that any of the students could be infected regardless of their proximity to the teacher, as the aerosols are distributed randomly in the room without ventilation.
If the room is ventilated during the lesson, either with fresh air or mechanically, and the classroom is stopped after one hour to completely recycle the air, the risk is significantly reduced.
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