The 2019 coronavirus disease (COVID-19) outbreak has stalled most major public events and gatherings for longer. This includes sporting events like the European football series, games that obviously cannot be played if social recommendations are followed. As efforts are currently being made to keep the season going under the existing restrictions, a preprint research paper published on the medRxiv * server describes the estimated incidence and risk of infection with the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2 ) in European soccer players.
Several previous studies showed that the risk of virus spreading during soccer games was negligible. As a result, in the second half of spring and summer, many games were played both in leisure time and as part of the professional season.
In the recreational variety of football, only a limited number of people were allowed to train together or play at the same time. Changing rooms and shower facilities were also banned for more than the required number of people, as social distancing outside the field was also emphasized.
In professional football, logs have been made to ensure the season is safe. In the UK, for example, the Department of Digital, Culture, Media and Sport has produced such a guide. Players and staff were tested once or more times a week to prevent infection of the player group. This would avoid the need for social distancing within this group within the club. It is noteworthy that the minimum frequency of testing to prevent the virus from entering a limited group is currently unclear.
In the current study, an attempt was therefore made to analyze the incidence of SARS-CoV-2 infections in this group of players and to compare it with that of the general population.
The researchers included top leagues from England, Sweden, Denmark, Germany and Russia. The analysis period lasted from the start of the season to January 2021, with the exception of Russia, where it extended from April to September 2020. The selected countries had extensive data on the number of players participating in the games, training and the number of player employees, as well as the number of infections that season.
Population data were obtained from the website of the European Center for Disease Prevention and Control (ECDC). The researchers calculated the incidence as the number of positive tests divided by the population, as well as an estimated incidence from an infection mortality rate of 0.35%.
The incidence among soccer players was calculated as the number of positive tests divided by the total number of players in a league. When the group was composed of both staff and players, as in the English Premier League, they calculated the incidence per week as the number of positive tests divided by the number of tests in a week. However, this results in a below average estimate of the incidence, as all players and staff are tested more than once a week, resulting in more testing than individuals.
The relative risk (RR) was calculated from the incidence.
Incidence in gamers and population
The researchers found that the incidence among soccer players ranged from 9% in Germany to 14.5% in Russia, compared with an incidence of 0.75% to 2.6% in Russia and Denmark, respectively. In Denmark and England the incidence was 10% and in Sweden ~ 13%.
The population incidence in England and Germany was 1.8%, in Sweden and Denmark ~ 2.5%.
The relative risk for the soccer players was between 2.85 and 17 and was greater than 1 in all cases. The highest RR was highest in Russia at ~ 17 and decreased in Sweden and Germany by 5 and 4.7 to 3.6 and 2.85 back in Denmark and England, respectively.
Based on the estimated incidence, the estimated RR was much lower, ranging from 0.9 to 1 in England and Germany, over 1.7 in Sweden to 2.56 and 3.5 in Denmark and Russia. In other words, the risk of SARS-CoV-2 infection in the soccer player group was higher in the last three countries compared to the general population risk.
What are the effects?
The number of infections in the population can be estimated using one of several methods. In the current study, the infectious mortality rate was used because of its relative fixity. When comparing positive tests from soccer players in top league soccer with the national incidence, it should be noted that positive tests are unevenly distributed across the age groups.
The most significant number of positive tests are in people between the ages of 20 and 29. This is the group that most soccer players also belong to. Because this group is likely to test positive far more often than other age groups or the general population, the risk of infection in soccer players is likely to be exaggerated compared to the overall community.
The reason for the high infection rate among soccer players despite frequent tests could either be that the test rate is still not high enough or that the virus spreads before the test becomes positive.
The researchers conclude with a quote from the UK guidelines for elite sport: “All individuals must adhere to government and PHE guidelines when away from the competition venue.” This seems like the best way to avoid infecting a soccer group and is little different from what is recommended to the general population.
* Important NOTE
medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be considered conclusive, guide clinical practice / health-related behavior, or be treated as established information.