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Super spreaders ensure explosive spreading

Some people infected with Sars-CoV-2 infect several people at once when they meet other people. Such explosive outbreaks are obviously a characteristic of the pandemic. Can demonstrations also become corona hotspots?

If the distance rules are not observed, demonstrations can become corona hotspots. Pictured: Demonstration against police violence, taken in Amsterdam on June 1st.

Eva Plevier / Reuters

The corona epidemic shows a different face in many countries after the first high phase. The events are dominated by so-called hotspots – places with explosive outbreaks, where an infected person infects several people at once and they then pass the virus on in their professional or private environment. In view of the anti-corona demonstrations now being held in many places and other meetings organized via social media, the question arises whether this behavior will now produce new corona hotspots.

Few infected people are responsible for most of the cases

The fact that an infected person can become several dozen or even a hundred cases within a few days – something like this happened in the past after church services, family celebrations, the gathering of Zumba classes and illegal and legal visits to restaurants or bars. Infections in slaughterhouses, logistics centers as well as nursing homes and dormitories also attract a lot of attention.

But mass outbreaks are apparently not a new appearance of the corona pandemic. Experts now even assume that such superspreader events are typical for the spread of Sars-CoV-2. Model calculations suggest that the pandemic was also fueled by mass outbreaks in the high phase. The team led by epidemiologist Gabriel Leung from the University of Hong Kong came to the conclusion that 80 percent of the Sars-CoV-2 transmissions there are due to only 20 percent of those infected. A research group from London led by Adam Kucharski even calculated that 10 percent of those infected worldwide are responsible for 80 percent of the transmissions. However, the London team only analyzed the situation until February 27th. At that time, the pandemic had not yet reached its peak in many countries.

Experts calculate the uneven distribution of infections using the kappa factor. The lower the kappa, the more a pandemic is determined by single events with mass infections. For Sars-Cov-2, the kappa value is between 0.1 and 0.4. The close relatives of Sars-CoV-2, the Mers and Sars viruses, also spread mainly through mass outbreaks. The influenza virus behaves differently: For the devastating flu pandemic of 1918/19, the calculated kappa value was 1.

Caution in closed rooms

Why certain infected people become super-distributors is still largely unclear. It could be that these people have a lot of viruses in the throat. Or they are particularly efficient distributors due to their way of speaking.

However, for a super-spreading event to occur, highly infectious people must meet many other people in an environment where virus transmission is successful. The hotspots that have occurred worldwide so far are characterized by loud speaking and singing, standing together and / or sitting closely over a longer period of time, but also by activities involving physical exertion.

According to current knowledge, an essential risk factor is also when all of this takes place in closed rooms. A Japanese study calculated that the risk of virus transmission indoors is almost 19 times higher than outdoors. Since almost all known superspreader events have started in closed rooms, some experts assume that – in addition to droplet transmission – transmission via aerosols also played an important role.

However, it is not out of the question that an outdoor demonstration or mass gathering can become a corona hotspot. On the one hand, it is conceivable that a highly infectious person infects all those who spend a long time in their immediate vicinity and with whom they shout slogans. It could also be the case that the expelled virus particles only survive in the air for a short time on a windy and sunny day and are also swirled. That would minimize the risk of infection. Because of such uncertainties, no expert currently dares to forecast the risk of demonstrations. The next few weeks will bring clarification.

Rapid isolation of suspected cases

Since an infected person cannot be seen to be a potential superspreader, and because infected people are usually contagious before the first symptoms, indoor events with a large number of people in corona times are not a good idea. The same may also apply to larger outdoor celebrations.

Not every workplace can be redesigned so that mass outbreaks can be completely prevented. Masks, on the other hand, could play an important role in closed rooms, since many of the virus particles of a potential super-spreader end up in the fabric and not in the ambient air.

The good news is that if the Sars-CoV-2 pandemic will continue to be driven primarily by superspreader events in the future, you can quickly identify a hotspot and immediately isolate everyone involved and contacts – even before the test results are available – effectively reduce the spread of viruses. That would save us all another lockdown.

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