A spin class gym in the Canadian city of Hamilton has been linked with an outbreak of 21 cases of Covid-19, with a further 100 people potentially exposed. The news was originally reported in the local press and cases have so far been found in one staff member and 20 patrons.

The outbreak comes amid months of speculation as to whether gyms and other indoor facilities hosting fitness classes are high-risk during the pandemic.

Concerns seem to focus on two main aspects of gyms which may make them high risk environments for viral transmission:

1) The number of high-touch surfaces, which may be used by multiple gym goers without effective sanitizing between uses, including weights, mats and machines. However, scientists generally now think that the risk of surface transmission of the coronavirus is smaller than originally anticipated, albeit studious handwashing is still recommended.

2) Person to person transmission via droplets and/or aerosols containing the SARS-CoV2 coronavirus. Droplet transmission has always been known to be a route of infection and more recently growing evidence has suggested aerosol transmission too. The difference between them being the size of exhaled particles. Heavy breathing during intense exercise is known to increase the production of these airborne particles, especially if patrons are unmasked.

In the case of the spin fitness gym in Canada, the business had reportedly implemented many extra safety measures. These included reducing capacity by half and giving a six foot radius between each bike and cyclist, as well as enhanced screening and sanitation measures. These measures complied with local public health guidelines.

However, these restrictions did not prevent the outbreak in this case and although difficult to definitively prove, airborne transmission would seem likely to be a large factor. Assuming bikes were effectively sanitized between uses and patrons physically distanced when entering and leaving the facility, it’s hard to conclude that transmission happened another way.

The outbreak is just one of several sourced to gym facilities in Canada recently. Ontario, where Hamilton is located along with the bigger cities of Toronto and Ottawa, is recording record Covid-19 case numbers with a 7 day average of over 700 cases per day. Recent data from Canada’s largest city, Toronto shows that in excess of one third of all Covid-19 community outbreaks can be traced back to bars, clubs and restaurants. Just as of yesterday, the provincial government shut down gyms, casinos and inside dining in restaurants and bars in the worst-hit areas, but Hamilton, where the spin class outbreak happened, is not yet under these restrictions.

Despite many health and fitness businesses following restrictions and public health guidelines to mitigate risk, it may be that the very nature of what they do makes it impossible to entirely make these places safe. High intensity exercise in an enclosed space with others is likely always going to carry some risk, especially in places with rising Covid-19 case numbers.