In contrast, indoor sporting activities require more attention. Direct aerosol infections may occur during contact sports, like wrestling or judo, where the athletes remain with their faces close to each other and may directly inhale the other athlete’s breath. The risk of indirect infections depends on the volume of the facility and the technical measures taken to improve the indoor air quality. In general, the infection risk is higher the smaller the facility and the more people occupy it. However, considering that (Olympic) sports facilities typically have very large volumes, it can be stated that the indirect infection risk is also rather low here. Exemplary calculations of relative infection risks can be calculated using on online tool provided by the RWTH Aachen (9).
Finally, there remain the premises jointly used by the athletes and coaches before and after the competitions, including changing rooms, toilets and physiotherapy facilities. These rooms are rather small and consequently virus concentrations may quickly reach critical levels. To avoid the buildup of virus concentrations in such rooms, they should ideally be well ventilated with outdoor air, e.g. by fully opening windows. Where this is not possible, technical ventilation solutions, like an efficient heating, ventilation and air conditioning (HVAC) system with either 100% fresh air supply or with efficient filters (like HEPA filters) shall be used. Alternatively, room air cleaners of a sufficient size can be applied. These air cleaners recirculate the air in the room and remove particles and viruses every time the air passes through the device. Usually the air cleaners are labelled with the clean air delivery rate (CADR). The room air volume should be recirculated and filtered multiple times per hour. For example, the German Umweltbundesamt recommends at least about six times per hour, i.e. the CADR in m³/h should be six time the room volume in m³, whereas the US Environmental Protection Agency recommends 4.875 times per hour. Blocken et al. showed that already an air exchange rate of 2.2/h resulted in a significant reduction of the infection risks in a gym (3).
In summary, the following recommendations for reducing the infection risks of athletes in sporting activities, including those during major sporting events like Olympic games can be given from an aerosol research point of view:
– Risks of a direct aerogenic infection during sporting activities is highest in contact sports, because minimum distances cannot be maintained. These risks are in general similar indoors and outdoors, but most contact sports like wrestling, judo etc. are indoor activities.
– Risks of indirect infections during outdoor sporting activities are extremely low due to the immediate dilution of the exhaled aerosol by the surrounding air.
– Indirect infection risks during any indoor sporting activities are significantly higher than during outdoor activities. They increase with decreasing volume and increasing occupancy of the facility.
In typical cases, where a low number of people are present in a rather large facility, the risk of an indirect infection can be considered to be moderate or low. The bigger the room the lower the risk of infection.
– The most critical environments are small rooms, like toilets, changing rooms and physiotherapy facilities. Due to the long residence time of viruses and virus-containing particles in the air, one may even get infected in these rooms without meeting another person. Protective measures like proper natural or technically enforced ventilation and/or air cleaning are highly advisable for such rooms and the proper use of efficient face masks is recommended wherever possible.
– In poorly ventilated indoor environments, the risk of an infection increases with the square of the residence time. Consequently, one should reduce this residence time whenever possible.
– In addition to strict regulations and hygiene concepts of the organizers regarding the protection against infections, it is recommended to inform all athletes and coaches of potential risks and ask for personal responsibility.
Since the knowledge base on SARS-CoV-2 and its aerosol transmission is still constantly growing and it cannot be ruled out that the virus will mutate further, the choice and scale of countermeasures may need to be flexibly adjusted according to the state of the pandemic (1).
■ Asbach C, Scheuch G
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Adami P, Cianca J, McCloskey B, et al. Infectious diseases outbreak management tool for endurance mass participation sporting events: an international effort to counteract the COVID-19 spread in teh endurance sport setting. Br J Sports Med. 2021; 55:181-182. doi:10.1136/bjsports-2020-103091
Asadi S, Wexler AS, Cappa CD, et al. Aerosol emission and superemission during human speech increase with voice loudness. Sci Rep. 2019; 9: 2348. doi:10.1038/s41598-019-38808-z
Blocken B, van Druenen T, Ricci A, et al. Ventilation and air cleaning to limit aerosol particle concentrations in a gym during the COVID-19 pandemic. Build Environ. 2021; 193: 107659. doi:10.1016/j.buildenv.2021.107659
Bulfone T, Malekinejad M, Rutherford G, Razani N. Outdoor Transmission of SARS-CoV-2 and Other Respiratory Viruses: A Systematic Review. J Infect Dis. 2021; 223: 550-561. doi:10.1093/infdis/jiaa742
Gesellschaft für Aerosolforschung. Position paper of the Gesellschaft für Aerosolforschung on understanding the role of aerosol particles in SARS-CoV-2 infection. 2021. https://doi.org/10.5281/zenodo.4350494 [27th May 2021].
Karimzadeh S, Bhopal R, Nguyen Tien H. Review of infective dose, routes of transmission and outcome of COVID-19 caused by the SARS-COV-2: comparison with other respiratory viruses. 2021; 149: e96. doi:10.1017/S0950268821000790
Ma J, Qi X, Chen H, Li X, et al. COVID-19 patients in earlier stages exhaled millions of SARS-CoV-2 per hour. Clinical Infectious Dieseases. 2020. doi: 10.1093/cid/ciaa1283
Morawska L, Cao J. Airborne transmission of SARS-CoV-2: The world should face the reality. Environ Int. 2020; 139: 105730. doi:10.1016/j.envint.2020.105730
RWTH. RisiCo Aachen University. 2021. https://risico.eonerc.rwth-aachen.de/ [27th May 2021].
Scheuch G. Breathing is enough: For the spread of influenza virus and SARS-CoV-2 by breathing only. J Aerosol Med Pulm Drug Deliv. 2020; 33: 230-234. doi:10.1089/jamp.2020.1616
Schumacher S, Schmid H, Asbach C. Effektivität von Luftreinigern zur Reduzierung des COVID-19-Infektionsrisikos. Gefahrst Reinhalt Luft. 2021; 81: 16-28. doi:10.37544/0949-8036-2021-01-02-18
Schwarz K, Biller H, Windt H, Koch W, Hohlfeld J. Characterization of exhaled particles from the healthy human lung - A systematic analysis in relation to pulmonary function variables. J Aerosol Med Pulm Drug Deliv. 2010; 23: 371-379. doi:10.1089/jamp.2009.0809
Shurlock J, Muniz-Pardos B, Tucker R, et al. Recommendations for Face Coverings While Exercising During the COVID-19 Pandemic. Sports Med Open. 2021; 7: 19. doi:10.1186/s40798-021-00309-7
van Doremalen N, Morris D, Holbrook M, et al. Aerosol and surface stability of SARS-CoV-2 as compared with SARS-CoV-1. N Engl J Med. 2020; 382: 1564-1567. doi:10.1056/NEJMc2004973