ObjectivesTo evaluate the restart of the German Bundesliga (football (soccer)) during the COVID-19 pandemic from a medical perspective.MethodsParticipants were male professional football players from the two highest German leagues and the officials working closely with them. Our report covers nine match days spread over 9 weeks (May to July 2020). Daily symptom monitoring, PCR testing for SARS-CoV-2 RNA twice weekly, and antibody tests (on two occasions—early during the phase in May 2020 and in the week of the last match) were conducted. Target variables were: (1) onset of typical COVID-19 symptoms, (2) positive PCR results, and (3) IgG seroconversion against SARS-CoV-2. All detected seroconversions were controlled by neutralisation tests.FindingsSuspicious symptoms were reported for one player; an immediate additional PCR test as well as all subsequent diagnostic and antibody tests proved negative for coronavirus. Of 1702 regularly tested individuals (1079 players, 623 officials members), 8 players and 4 officials tested positive during one of the first rounds of PCR testing prior to the onset of team training, 2 players during the third round. No further positive results occurred during the remainder of the season. 694 players and 291 officials provided two serum samples for antibody testing. Nine players converted from negative/borderline to positive (without symptoms); two players who initially tested positive tested negative at the end of the season. 22 players remained seropositive throughout the season. None of the seroconversions was confirmed in the neutralisation test.ConclusionProfessional football training and matches can be carried out safely during the COVID-19 pandemic. This requires strict hygiene measures including regular PCR testing.

Objectives Elite professional football players and staff are a unique group that might give insight into the epidemiology of SARS-CoV-2 infections in Germany and thus can serve as a model for a geographical distribution and an estimation of undetected infections. Methods In this prospective cohort study seroprevalence was determined twice in May and June 2020 in players and staff from German Bundesliga. As screening assays a commercial ELISA (Euroimmun) and a CLIA (Roche) was used and an in-house neutralisation assay (NT) as gold standard. Participants were tested twice weekly using PCR from nasopharyngeal and/or oropharyngeal swabs. Results Seroprevalence (NT used as confirmation) in 2,164 samples from 1,184 players and staff was rather similar in May (23/1157 (1.99%)) and in June (21/1007 (2.09%)). All participants were PCR negative during the study period. Significant regional differences in seroprevalence were not observed. When comparing seroprevalence with the cumulative incidence of infections derived from the German notification system (subgroup matching to cohort; men, age: 20-69), IgG was found 8-10 times more frequently, pointing to a high rate of undetected infections. ELISA and CLIA correlated only moderately (Kappa 0.52). Conclusions Seroprevalence with high quality diagnostic in Germany seemed to be around 2%. The number of undetected infections seems to be 8-10 times higher than notification data. Quality of antibody assays is rather variable, thus results should ideally be confirmed at least by a second assay to prove IgG positivity.