Coronavirus: Scientific investigations of Transmission
It is known that the Coronavirus SARS-CoV-2 of human-to-human transferable. The main route of transmission appears to be according to current knowledge, the droplet infection. However, much of what relates to the risk of Infection is still unclear. Researchers have therefore focused on the different transmission paths.
The novel Coronavirus is primarily transmitted via droplet infection and most likely on the nose, which was shown by a study recently. In addition, there is evidence that SARS-CoV-2 can be transmitted via aerosols, explains the Federal centre for health education (BZgA) on your Portal “infektionsschutz.de”. Also a Transmission via faeces seems to be possible. However, a final evaluation is still difficult.
Still no final clarification
How exactly is the Coronavirus SARS-CoV-2 is widely used – whether it is mainly a droplet infection, or via aerosols in the respiratory air is not yet finally clarified, said in a recent communication from the Technical University (TU) Berlin.
If a Corona-infected Person coughs, speaks or sneezes, produces a beam of different-sized droplets, and aerosols that penetrates into the air and spreading. All of these differently sized droplets and aerosols can potentially contain viruses.
How these particles behave, if and when you fall to the ground, how far they spread, in the air, stay where you are or where you settle, is a current research topic of Prof. Dr. Martin Kriegel, head of the Hermann-Rietschel-Institute at the TU Berlin.
Residence time of pathogens in the air is investigated
“We are investigating in various projects, the residence time of pathogens in the air under various conditions,” explains Martin Kriegel.
In connection with the Corona-pandemic, scientists are investigating the extent to which depends on the spread of the Virus of the composition and size distribution of the particles within the exhaled air (Aerosol).
In the case of an Aerosol (airborne droplet nuclei smaller than 5 microns; for comparison: A human hair has a thickness of about 100 micro-meters) is the smallest liquid or solid particles (which can be, for example, viruses, individually or in conjunction with Saliva or soot, fine dust, etc.) in a Gas, usually air.
Also the room air-conditioning and Ventilation play a role
“For the Corona Virus seems to show that both droplet infections as well as airborne Transmission through aerosols, are relevant,” says Martin Kriegel.
As the communication explains, is a droplet infection, the virus particles in saliva droplets directly on the mucous membranes of another person. In the case of a air-borne Transmission of the pathogen reach – bound in the smallest liquid particles in the respiratory tract.
For the behavior of viruses in the air, the size of the carrier aerosols is crucial, but also the indoor climate, the air exchange rate, and the way is revealed.
“Larger particles fall faster to the ground. Smaller particles follow the air stream and can long remain in the air,“ Martin Kriegel.
Smaller particles in the room air greater fall to the ground
The information suggests that the propagation takes place in the space of the mixture of particles, saliva and air that is produced while Talking, coughing and Sneezing, in two steps.
First, it is produced by the coughing/Talking/Sneezing a beam that penetrates into the indoor air and, increasingly, with this mixed in. The history of the incoming beam is, according to the experts, depending on various conditions such as the speed, the turbulence, the temperature difference between the jet and the ambient air, as well as the difference of the humidity.
From various scientific studies, it is known that when you Speak/cough/Sneeze particles of 0.01 µm to 1500 µm occur.
“After the complete mixing of the jet with the ambient air, the distribution takes place,” explains Martin Kriegel.
“The smaller particles closely follow the ambient air flow, while larger particles fall gradually to the ground. But what is often ignored is the fact that the man emitted only when Sneezing is very large the particle is. During normal speech and a cough, almost exclusively, small aerosols are generated.“
Certain circumstances favour the spread in the room
In various projects, the scientists have measured indoor and scientists, the so-called sedimentation time (deposition time) of particles of different size classes. Small particles (0.5 to 3 microns) are, therefore, after a measuring time of 20 minutes, almost completely in the air.
A Deposit of these particles is not or only slightly recognizable. For medium-sized particles (3 to 10 µm), after a measuring time of 20 minutes, however, yet to find more than 50 percent in the air.
“A further study shows that larger droplets (>60 µm) can spread under certain circumstances in the far room. This is the case, for example, if the particles in the buoyancy flux of the heat sources (emits, for example, of a Person). They rise, spread horizontally, and start only then, the Deposit. Any horizontal movement of the air to strengthen the dissemination effect,“ explains Martin Kriegel.
Any increase in the supply of outdoor air is useful
In connection with the resumption of a professional everyday life in a with several people occupied the office, the researchers, the particles spread in a with four people occupied the office with and without mechanical ventilation are simulated.
“This shows that smaller particles under 50 microns spread without mechanical ventilation, far in the room and linger long. In contrast, particles between 5 and 20 microns wide in a room with mechanical ventilation less far and be dissipated to a large extent,“ says Martin Kriegel.
“The crucial questions that we now investigate in interdisciplinary projects, are to be, how big SARS-CoV-2 particles to be infectious and as the residence time of this particle size through targeted may influence the supply and exhaust air systems or simple Ventilation of rooms,” says the expert.
“The climate plays a role, because the aerosols through evaporation very quickly smaller and then behave differently. Basically it can be stated that in the case of typical air exchange rates in residential and office buildings remain, the excitation over hours in space. The rate of descent and also the air renewal take a very long time. Any increase in the supply of outdoor air is therefore generally useful.“ (ad)