The longer research observes the coronavirus, the clearer the ways in which it spreads also become. The focus is more and more on the so-called aerosol particles – microscopic airborne particles that are spread through the air we breathe.
What are aerosols?
Aerosols are solid or liquid particles that are so small that they are hardly subject to gravity. Unlike the droplets ejected when coughing or sneezing, these tiny particles do not sink quickly to the ground, but rather float in the air for much longer – sometimes minutes or even hours. So someone who enters an unventilated room after being infected can become infected. In addition, droplets cannot be inhaled as strongly as aerosols. Most of the time, they’re more likely to stay in the upper airways, while aerosols can penetrate deep into the lungs.
Some diseases are known to be partly transmitted this way, for example tuberculosis. Direct contact with an infected person is not necessary in order to be infected.
What are the findings with regard to the coronavirus?
Initially, a possible infection by aerosols hardly played a role in the consideration. However, doctors around the world have analyzed corona outbreaks in more detail. And gradually they discovered that there could hardly be any other explanation for numerous outbreaks than an infection via aerosols.
One can only speak of this, however, when people were very far apart and still infected. Initial evidence of this came from Chinese researchers who were following up chains of infection in a restaurant in Wuhan – the city where the virus first became apparent. The re, guests were sick with the coronavirus who sat at different, far apart tables and had no other common paths or encounters.
The World Health Organization now also regards aerosols as an important transmission route for the virus. This has an impact on the recommendations on health protection, at least in the medium term.
Staying in poorly ventilated rooms increases the risk
The y arise when breathing and speaking, but especially when screaming and singing.
According to the RKI, staying longer in small or poorly ventilated rooms can increase aerosol transmission even over a distance of two meters. This finding also plays a role, for example, when considering how, for example, classrooms can be better ventilated – because that seems to be a key to reducing the aerosol pollution of the breathable air.
With the air purifier against aerosols?
A research team at the Goethe University in Frankfurt found out through a study that commercially available air filters can significantly reduce aerosol pollution. In a large-scale experiment, the scientists set up four air purifiers with so-called HEPA filters in a classroom and determined the concentration of aerosols in the air.
The re were 27 students in the room, windows and doors were closed during the measurement. As a reference value, the scientists gave the concentration of aerosols in a neighboring classroom without an air purifier.
Transmission within a radius of more than eight meters
The Helmholtz Institute for Infection Research published the first results of a study on the outbreak in the Tönnies meat factory in July Rheda-Wiedenbrück. According to this, an employee in cattle cutting transmitted the virus to several people in May, within a radius of more than eight meters.
The study also showed that workers’ living conditions did not play a major role, the researchers said.
How long do aerosols stay in the air?
US researchers carried out an experiment in which test subjects in a closed room say the short sentence “Stay healthy!” For 25 seconds. should repeat out loud. Because of the counted micro-drops, the scientists assume that a corona-infected person, when speaking normally, emits around a thousand virus-contaminated droplets per minute on average, which float in the room air for about eight minutes.
Another study comes to the conclusion that the particles can be detected in the air for up to three hours. However, the researchers experimented with artificially produced aerosols, which “differ fundamentally from coughing / sneezing patients with Covid-19 in normal social interaction,” as the Robert Koch Institute emphasizes. Whether and how quickly aerosols sink also depends on factors such as room temperature or humidity.
Dominant route of infection via aerosols?
The importance of the suspended particles in the spread of the virus is very high.
But there are also voices that attach a less important role to aerosols in the transmission of the coronavirus: A team from Harvard Medical School published an analysis in which it is argued that virus transmission via aerosols could not be the dominant route of infection for the coronavirus . A sick person infects fewer people than with other aerosol-borne diseases, they write.
Correct ventilation – is that the solution?
You can cut the risk in half if you bring in twice as much air, said Kriegel at a joint press conference with Federal Health Minister Spahn. A shorter stay also reduces the risk of infection: “If we cut it in half, we cut the risk in half too.”
“However, the window ventilation is not reliable,” said Kriegel in an interview with the editorial network Germany. Because in individual cases you don’t know how much air is getting through the window.
The effectiveness of window ventilation depends on how strong the wind blows outside and how big the temperature difference between inside and outside is.
“A lot of people think that when it’s cold inside, the air inside is fresh. That’s not true. So you always have to open the windows completely at regular intervals. Because a tilted window doesn’t really let in much air.” This is a big challenge, especially now, in the colder season. “If you only open the window for five minutes, it will not be enough to remove the contamination in the interior,” the researcher and his team have found.
School lessons as a source of danger?
The break should be much longer and there should be more ventilation. And the lesson times actually be shorter. ” A single infected person in a room could infect all the others, especially since the time spent in the classrooms was relatively long and the ventilation situation was in many cases insufficient.
In addition, the head of research urgently advocates wearing a mask all the time in class: “90 percent of the aerosols bypass the edges of the mask, but the masks prevent the other person from receiving my airflow. Instead, the airflow is diverted.
The aerosols get into the Room air, but no longer in a highly concentrated form on my counterpart. ”
How dangerous are air travel?
With regard to air travel, there is no risk for passengers, at least from the perspective of aircraft manufacturers and airlines. Airbus emphasizes that a complex and closed ventilation system ensures very clean air and a low risk of infection on board.
The air in the cabin is renewed every two to three minutes and corresponds to the quality in a hospital. In addition, the air constantly flows down from the ceiling and is extracted again on the floor.
How high the risk of infection in airplanes could really be is, however, controversial – because of the proximity of the passengers to each other, because the aerosols are not withdrawn immediately and because the air conditioning systems only work at full capacity during flight operations.
(Stand: 10.10. 2020)
Further articles on the coronavirus
We have created a news blog. In view of the large amount of information, this provides an overview of the most important current developments.
+ Current developments: Figures on the coronavirus in Germany (as of January 16)
+ High numbers of corona infections: is the incidence value 50 correct? (As of January 5th)
+ New rules: This is how the federal states implement the resolutions (as of January 14)
Test and protection
The vaccination ordinance: who will be vaccinated first, who will be vaccinated later? (As of December 26th)
+ Dates: How, when and where can I get vaccinated? (Status: 9.1.)
+ Biontech and Pfizer: What is known about the side effects of the corona vaccine (as of January 14th)
+ Protection: So it is about the development of vaccines against the coronavirus (status: 06.01.)
+ Corona infection: how reliable are the tests? (As of: January 13th)
+ Sick people: New findings in the search for drugs (as of January 6th)
+ What is the situation like in the hospitals? (As of: January 13th)
+ Economy: How the world of work deals with the number of infections (as of January 11)
Contagion and Transmission
+ Virus variants: how dangerous are the new coronavirus mutations? (Status: 02.01.)
+ Opponents of infection protection measures: What AfD and lateral thinkers have to do with the spread of the coronavirus in Germany (as of December 17)
+ Transfer: What role do aerosols play (as of 10.10.)
+ Excess mortality: How deadly is the coronavirus really? (As of: January 9th)
+ Travel warning:
The current list of risk areas (as of December 24th)
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