COVID-19 Outbreak Among Attendees of an Exercise Facility

Chicago, Illinois, August-September 2020

Frances R. Lendacki, MPH; Richard A. Teran, PhD; Stephanie Gretsch, MPH; Marielle J. Fricchione, MD; Janna L. Kerins, VMD


Morbidity and Mortality Weekly Report. 2021;70(9):321-325. 

In This Article


This outbreak reinforces the need for combined COVID-19 prevention strategies, including universal mask use in public settings when persons are with others who do not live in the same household, especially indoors***; testing of symptomatic persons and those who have been exposed to SARS-CoV-2; self-isolation after symptom onset or a positive COVID-19 test result; and quarantining of persons who have been exposed to SARS-CoV-2.[3] Cases were identified among 68% of facility attendees, and CDPH attributed this outbreak to the high proportion of attendees with COVID-19 who participated in class while symptomatic, or asymptomatic and infectious. Most attendees did not wear a mask during exercise class; infrequent mask use when participating in indoor exercise classes likely contributed to transmission. In addition, the potential for infected persons to infect others between their testing date and receipt of test result reinforces the need to quarantine while waiting for a COVID-19 test result and avoid gatherings while unknowingly infectious.

Data on transmission of SARS-CoV-2 in exercise facilities are limited; outbreak reports indicate that increased respiratory exertion might facilitate transmission.[4–7] Clusters of SARS-CoV-2 transmission associated with exercise groups were reported before COVID-19 was declared a pandemic and before mask use was broadly recommended.[5,6] In a more recent outbreak related to an indoor hockey game, only athletic face shields partially covering the nose and mouth were used.[7]

Although the timing of cases suggests a point-source exposure, none was identified. Most interviewees attended several exercise classes. Some published evidence supports aerosolized transmission of SARS-CoV-2,[8] which could have been a contributing factor in this outbreak. Although the facility's ventilation system was not assessed, inadequate air circulation might have exacerbated transmission in the building, which was not originally designed for exercise classes.[9]

The findings in this report are subject to at least five limitations. First, because of incomplete interview and testing data, the cases might have been undercounted. Second, not all interviewees reported their class attendance or in-class behaviors, which limited the ability to link cases to particular classes and assess differences between attendees who did and did not have COVID-19. Third, reliance on self-reported behaviors and COVID-19 case status might have introduced recall and social desirability biases. Fourth, nonresponse and the small cohort size limited the precision of effect estimates. Finally, whole-genome sequencing was not performed to assess the phylogenetic relationships among cases linked to the exercise facility, and some attendees with COVID-19 might have acquired different strains of SARS-CoV-2 elsewhere in the community.

The outbreak described in this report occurred despite use of certain COVID-19 mitigation measures. To reduce SARS-CoV-2 transmission in exercise facilities, employees and patrons should wear a mask, even during high-intensity activities[10] while ≥6 ft apart.††† In addition, facilities should provide engineering and administrative controls including improving ventilation, enforcing physical distancing, increasing opportunities for hand hygiene, and reminding all employees and patrons to 1) isolate when experiencing COVID-19–like symptoms or after receiving a positive SARS-CoV-2 test result and 2) quarantine after a potential exposure to SARS-CoV-2 and while awaiting test results. Conducting exercise activities entirely outdoors or virtually could further reduce SARS-CoV-2 transmission risk.

†††Per CDC guidance, persons who are unable to wear a mask because of difficulty breathing during high-intensity activities must choose a location with greater ventilation and air exchange (e.g., outdoors versus indoors) where it is possible to keep ≥6 ft from others during activity.