Spread of covid-19 during soccer matches

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Any person who is involved in a contact sport is currently in a state of uncertainty as data about the behavior of covid-19 are still unavailable. The scientific community is feverishly working to produce such data.

If you have asked “what are the chances to get infected by playing soccer?”, you are not alone. This question is in the minds of every player (pro or otherwise) and every organization (again, pro or otherwise). A paper providing some data towards the answer of this question has appeared in the preprint server for health sciences.

The paper’s authors used data from 14 matches of the Danish Superliga. They assumed a single infected player and they defined the Danger Zone (DZ) as a circular area of radius 1.5 meters. Then, they used data from GPS trackers and calculated the time each of the remaining players spent inside the DZ. In addition, they had to add some reasonable assumptions about the effect on a healthy player passing through an area previously occupied by the infected player. They quantified the final result for each player with an exposure score which can be converted to an exposure time.

The conclusion of the paper is that the average exposure time for each player is 1 minute and 28 seconds. However, there is a big variation to actual exposure time from zero to as much as 15 minutes depending on position and tasks performed in the pitch. In general, strikers are at risk the most and goalkeepers the least.

Given the present understanding of the virus, it is not clear what exactly the previous statements imply. We only know that the longer the exposure, the greater the chances to get infected and the higher the severity of the illness. But what is long and short exposure, as well as intensity of exposure is still unknown.

The study has also certain inherent limitations. First of all, the assumptions introduced for the calculation are based on educated guesses and not accepted medical standards. The latter will be the outcome of the current research activity and will become available only in the future. Then, the study takes into account only one infected player. However, more may exist. The authors state that for more players the effect is linear (i.e. just multiply by the number of players). However, this statement needs a thorough checking.

Finally, the study limits itself only to the `risk through proximity’ and ignores transmission through other mechanisms, for example through physical contact of the players or transmission through contact with a third object. Perhaps the virus can pass to the clothes of a healthy player even during a brief exposure and later he/she can get infected after touching his/her clothes. Or a healthy player may get infected through long distance after the virus transfers to the ball and from there to the player.

As a final remark, players in youth leagues do not have the same mobility as pro players. Their games also last slightly less time. Therefore, the exposure will be less, whatever that means.

Read the actual paper: Spread of virus during soccer matches by N.S. Knudsen, M.M.D. Thomasen, T.B. Andersen.

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