The virologist Adam Grundhoff examined the corona outbreak in a Tönnies slaughterhouse and found that the infection occurred over eight meters from an infected person. In everyday life, however, aerosol transmission over such a distance is unlikely, Grundhoff said in the Dlf.
A so-called superspreading event was responsible for the corona outbreak at the Tönnies slaughterhouse in Rheda-Wiedenbrück. The SARS-CoV-2 virus was transmitted to several people within a radius of more than eight meters. This is the result of a study by scientists from the Helmholtz Center for Infection Research (HZI), the University Clinic Hamburg-Eppendorf and the Leibniz Institute for Experimental Virology (HPI). The locations of infected people at work and the infection chains were analyzed using virus sequences.
To find answers, the team of scientists meticulously reconstructed who was infected by whom in the Tönnies slaughterhouse in early May, using DNA-based detective work. Professor Adam Grundhoff from the Leibniz Institute for Experimental Virology in Hamburg was instrumental in the search for traces.
Researcher: Could very well investigate outbreak events
Ralf Krauter: How did you go about tracing the chains of infection?
Adam Grundhoff: As you say correctly, that was at the beginning of May, it was a relatively limited outbreak at the time, which was about a month before the very, very large outbreak at Tönnies, which was then in the press everywhere. Around 30, 40 infected employees were involved. This was a very limited outbreak that we were able to investigate very well.
We knew everyone who was involved, they all belonged to the same shift, and we knew where they were on the assembly lines in this slaughterhouse. That means we knew exactly how they were positioned among each other in this slaughterhouse. These were, of course, good starting points for trying to clarify what the transmission chains were like.
So it does matter that they were close to each other, we could say, this infection went from one employee to the other because almost all infected people are very close to this one person. So we looked at that. We looked at how they are in the room, where are they positioned on the assembly lines. It has to be said that there was an initial suspicion. So there were two people who indicated that they had contact with two other people from another meat processing company who tested positive afterwards. So the two came into question.
We then took a closer look at it there and, among other things, also analyzed the genome sequences of these viruses to find out: How could the transmission chains have been there?
"It has to be an aerosol transfer"
What quickly turned out to be that one of the two cases that came into question was eliminated because it had a mutation that was not passed on. That said, that couldn't be the index case. The other one had a signature or a fingerprint, so you can call it, which you found in all other cases. That means you could assume that this was actually the index case.
We then took a closer look at it, and in fact it is the case that almost all infected people stood close to this person on the assembly line and also had fixed working positions there. It was actually quite clear that a transmission was obviously taking place here in this workshop during work and during the early shift. What was interesting is that this transmission took place over a greater distance, i.e. clearly over 1.5, two, three meters, but up to eight meters. This is practically something that traditionally has to be an aerosol transmission, because droplet infections do not work over this distance.
Krauter: In the end, does this mean that a single super spreader ultimately led to this avalanche rolling in and a total of 1,400 employees being infected in this slaughterhouse in Rheda-Wiedenbrück in the medium term?
Grundhoff: Yes, you could assume that. Although you have to say, superspreaders, I personally don't like the word, we prefer to speak of a superspreading event. Superspreader, that suggests that this person had a characteristic that was special, that is, it was culpable. This was not the case in this case. These are clearly the conditions there at the workplace, i.e. the cooling, the fact that they are close to each other. It was a super spreading event. These same mutations, the characteristic ones, can be found later in cases in this company at Tönnies. One could assume that this was the starting point, also of the later big outbreak.
Eight meter transmission very rare exception
Krauter: The role of the aerosols, which you have already mentioned, that is, the finest liquid droplets during transmission, has been known for a long time. What is new is the surprising realization that this transmission can now go over relatively long distances - eight meters, you mentioned it. This has been proven by you in this reconstruction of the infection routes. What does that mean for the distance rules in social distancing that we have all got used to? Do they generally need to be put to the test or maybe enlarged?
Grundhoff: In general, probably not, it certainly depends on the situation. Of course, many will not be surprised that it is eight meters. Since many have already suspected that under these special circumstances in these meat processing companies - it is cooled there to ten degrees, the air is constantly circulated. As I said, they are close to each other, they do hard physical work, it is very loud there, so they have to speak loudly, these are all conditions that certainly favor this aerosol transmission. When all of this comes together, you have to be very careful.
We didn't look at how the individual components interact. You need other methods for this. There are other people who have this as a specialty, they also look at something like that. But if you only have one of these components, that doesn't mean that you have eight meters of transmission. If you only have air circulation but a relatively high temperature, then you probably won't have transmission over these distances. You have to look at that in detail now.
In the circumstances you encounter in everyday life, an eight-meter transmission will certainly be the very rare exception, rather than the rule. These results can really only be applied one to one to the very circumstances that we had in these meat processing industries. Of course this is highly relevant for them, there these conditions or working conditions. You can find them everywhere, of course, and you really have to look at them now: What are the adjustment screws - to change individual parameters and prevent transmission.
Comments from our interlocutors reflect their own opinions. Deutschlandfunk does not adopt the statements made by its interlocutors in interviews and discussions.
