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The Team Sports Risk Exposure Framework (TS-REF) was developed in July 2020 by experts in sports medicine, virology, sports science and public health to facilitate the safe return of sport during the COVID-19 pandemic.1 The TS-REF was developed at the time when the outdoor transmission risk of SARS-CoV-2 during sport was unknown. The TS-REF has been adopted by Public Health England and the UK Government (Department for Digital, Culture, Media and Sport), for use within both elite and community sports,2 to both determine the risk of SARS-CoV-2 transmission during specific sporting activities (eg, rugby tackle),1 and to identify and isolate increased risk contacts during sport.3 The TS-REF classified increased risk contacts as player-to-player interactions ‘within 1 m, directly face to face, for 3 or more seconds’.1
Increased risk contacts as defined in the TS-REF were studied in rugby league, following interactions with eight infectious players across four matches.3 Increased risk contacts were monitored for 14-days during their isolation period and serially tested for SARS-CoV-2. Of the 28 identified increased risk contacts from the matches, only one player subsequently tested positive for SARS-CoV-2, which was linked to an internal club outbreak and believed unrelated to training activities. Another study in professional soccer observed similar findings,4 collectively suggesting the risk of outdoor transmission during sports appears lower than first thought.3 4 Consequently, the TS-REF may require players to unnecessarily isolate who are not at an increased risk of infection. Our aim was to update the TS-REF based on our evolving understanding of SARS-CoV-2 transmission during sports.
Team Sport Risk Exposure Framework 2
SARS-CoV-2 can be transmitted by both exhaled large ‘ballistic’ respiratory (>100 µm diameter) and aerosol (<100 µm diameter) droplets. Aerosol droplets are higher risk, as they rapidly evaporate to become small aerosol particles (<50 µm diameter) that can be easily inhaled.5 6 Indoors (eg, spaces with poor ventilation), these smaller aerosol droplets can form clouds of aerosol particles, increasing the risk of transmission to those in close proximity. Outdoors, exhaled aerosol particles are dispersed more rapidly from greater air velocities, although this will become less pronounced at close proximities and when directly face to face. Since the design and implementation of the TS-REF, new variants of SARS-CoV-2 have been identified. While initially new variants were thought to be more transmissible, this has been debated more recently.7 8 Therefore, we propose that TS-REF-2 should apply to all SARS-CoV-2 variants unless new evidence emerges.
The TS-REF-2 (figure 1) is based on the original TS-REF, with five additions (online supplemental figure 1), to address the greater risk of transmission indoors and observed lower risk of transmission outdoors during sport.3 4A detailed explanation of changes are presented in online supplemental table 1.
The TS-REF-2 can be adopted by both elite and community sports, to identify individuals who are required to isolate, if deemed to be increased risk contacts. The TS-REF-2 is based on respiratory aerosol and droplet SARS-CoV-2 transmission, and the parameters which would likely reduce or increase the transmission risk (ie, player proximity, face to face or other, environmental (indoor or outdoor) air characteristics). As such the TS-REF-2 can be applied to sporting populations of all ages, given similar SARS-CoV-2 transmission rates are observed across ages and competition levels, although lower transmission rates have been observed in under 10 years.9 Fundamentally should an individual have a close proximity, face to face, non-fleeting interaction with an infectious individual, they are at an increased risk of SARS-CoV-2 transmission, in comparison to if the interaction was not at close proximity, not face to face and fleeting in nature. Furthermore, given ventilation is likely lower indoors compared with outdoors, the SARS-CoV-2 transmission risk is greater indoors than outdoors (due to lower aerosol dispersion), and the extent of the interaction with an infectious individual also should be considered (eg, single, multiple or cumulative duration). Where interactions occur between individuals who are mask wearing, a less cautious approach to identifying increased risk contacts may be considered, given the reduced likelihood of exposure to infectious respiratory aerosols and droplets. The TS-REF-2 can be used during training and match activities, and serve as a supplementation to broader public health definitions in other contexts (eg, changing room, team meeting or car share).
Determining indoor and outdoor activity
While the TS-REF-2 proposes a framework to identify increased risk contacts, differentiating indoors and outdoors spaces in sport can be challenging. For example, consider a stadium with an enclosed roof, or temporary building with no/limited sides. The key considerations for determining an indoor or outdoor environment can be established from online supplemental table 2, based on the volume, the presence of a roof or ceiling and air velocity characteristics. The indoor TS-REF-2 definitions should be applied when the sporting environments has two or more indoor characteristics. Volume, the presence of a roof or ceiling, air velocity at low level, density of people, CO2 and environmental conditions should be considered collectively when determining the SARS-CoV-2 transmission risk, and if the TS-REF-2 should be applied following the indoor or outdoor definition. For example, a large space may appear ‘outdoors’, yet if air movement at low level is poor (ie, low air velocities) the formation of clouds of aerosol particles is possible, increasing the risk of transmission.
The TS-REF-2 considers the transmission risk of SARS-CoV-2 during indoor and outdoor activities, building on the previously adopted TS-REF. Healthcare professionals and policy-makers can determine if the sporting activity was undertaken in an indoor or outdoor environment and then apply the TS-REF-2 to identify increased risk contacts. The TS-REF-2 can be applied to both training and match activities, for both professional and community sports, when implementation can be achieved with an appropriate level of precision. Review of video footage if available will provide a higher degree of accuracy in defining the types of interactions between players. These recommendations should be continually reviewed and updated as the evidence related to the transmission risk of SARS-CoV-2 continues to evolve. Ultimately, sports should aim to undertake as much activity as possible outdoors given the lower SARS-CoV-2 transmission risk compared with indoor activities.
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Twitter @23benjones, @drkeithstokes, @drsimonkemp
Contributors BJ, GP, KAS and SK conceptualised the initial TS-REF framework. BJ and GP conceptualised the initial draft of the TS-REF-2. BJ, GP, MC, KAS and SK developed and finalised the TS-REF-2 framework, and developed online supplemental table 1. CB, BJ and GP developed online supplemental table 2. BJ and GP drafted the manuscript. CB, JC, MC, NP, CR, JS, KAS and SK provided reviews and editing of the manuscript. All authors critically reviewed and edited the manuscript prior to submission.
Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Competing interests BJ and GP are employed in a consultancy capacity by the Rugby Football League. KAS and SK are employed by the Rugby Football Union. MC is employed by Premiership Rugby. CR is employed by South Africa Rugby Union. GP, JC and JS are employed by Public Health England.
Provenance and peer review Not commissioned; externally peer reviewed.
Supplemental material This content has been supplied by the author(s). It has not been vetted by BMJ Publishing Group Limited (BMJ) and may not have been peer-reviewed. Any opinions or recommendations discussed are solely those of the author(s) and are not endorsed by BMJ. BMJ disclaims all liability and responsibility arising from any reliance placed on the content. Where the content includes any translated material, BMJ does not warrant the accuracy and reliability of the translations (including but not limited to local regulations, clinical guidelines, terminology, drug names and drug dosages), and is not responsible for any error and/or omissions arising from translation and adaptation or otherwise.
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