This report shows that transmission of SARS-CoV-2 can occur during indoor sporting events despite the implementation of a hygiene concept, in particular in the absence of PCR testing for SARS-CoV-2 for all asymptomatic participants prior to events taking place. There was no in-depth laboratory analysis of SARS-CoV-2 in November 2020 (with respect to the precise SARS-CoV-2 virus type involved) during which time this event took place. At the time this report was written, there were no further laboratory samples available from the respective infections suffered at this event, therefore a further retrospective molecular analysis was not possible.
Our data clearly support the notion that wearing facial masks reduced the rate of infection11. Surprisingly, in our retrospective study we did not detect a difference in transmission in persons that were allocated to stay in zone 1, 2 or 3. However, since contact time and time spent in the respective zone was not monitored continuously this does not allow to conclude that distancing is useless. There is strong evidence that distancing helps to contain spreading of SARS-CoV-212,13,14. Of utmost interest, however, participants who continuously wore a particle filter masks (category KN95/ FFP2 or higher) were fully protected. This strongly suggests that appropriate protective equipment is able to prevent SARS-CoV-2 transmission and that particle filter masks are especially useful in this regard.
As it is not possible to wear medical face masks whilst undertaking an intensive, physically demanding sport such as professional basketball, it is likely that infection resulted from airborne transmission of SARS-CoV-2 and played a major role in participants contracting SARS-CoV-2 within the basketball stadium during the match. These findings correspond with other reports which have observed the transmission of SARS-CoV-2 during rigorous physical activity15,16,17 in particular indoor activities18,19. Interestingly, a recent study carried out in the sport of rugby—which is not played indoors—has shown that there appears to be no risk of SARS-CoV-2 transmission20. Nonetheless, experience gained during the UEFA EURO 2020 event clearly shows that the behavior of spectators can critically contribute to SARS-CoV-2 transmission rates during outdoor sport events in general, especially in scenarios where many spectators are present12. Overall, the infection risks of carrying out sporting events indoors and outdoors with respect to transmission of SARS-CoV-2 have not been finally established yet. However, it appears likely that the risk of SARS-CoV-2 transmission in an indoor sporting environment is higher.
Since asymptomatic people substantially contribute to the spread of SARS-CoV-221, testing of active participants prior to the sport event may be a suitable measure to reduce the risk of SARS-CoV-2 transmission. This testing strategy may also include vaccinated participants, since vaccination does not necessarily prevent infection and dissemination of SARS-CoV-2 infection under all circumstances22,23. Antigen tests seem not to be sufficient to identify all potentially SARS-CoV-2 positive sport participants24. Consequently, in the future it appears to be important to carry out PCR tests for detecting possible asymptomatic SARS-CoV-2 infections amongst actively participating players especially prior to indoor sporting events in order to prevent the mass transmission of this disease.