Study population and setting
This study identified cases from fitness dance classes in 12 sports facilities in Cheonan, South Korea, from a cluster traced to a February 15th workshop for fitness instructors. From the 27 instructors who attended, 8 (29.6%) tested positive for SARS-CoV-2. There were 112 COVID-19 cases that resulted from the workshop, including people who took classes with infected instructors, transmission from infected instructors to family members, and coworkers/acquaintances who attended meetings with infected instructors.
Summary of Main Findings
Of the 112 COVID-19 cases associated with this outbreak, 82 (73%) were symptomatic. Instructors with mild symptoms continued to teach classes until the sports facilities closed — about a week after their symptom onset. The classes ranged in size from 5 to 22 students in a room of about 60 square-meters, for roughly an hour of intense exercise. Students who developed illness began experiencing symptoms an average of 3.5 days after the class. The majority (51%) of the resulting cases were thought to be due to instructor-to-participant transmission, while another 34% (n=38) were due to intra-family transmission from the instructors, and 15% (n=17) were due to transmission during meetings with coworkers. The attack rate (i.e., proportion infected of those exposed) was estimated at 26 % (95% CI: 21 – 33%).
The study used systematic contact-tracing that allowed the researchers to identify primary, secondary, and tertiary transmission cases. The study also noted case-contact relationships (e.g., coworker, family members, etc.).
Investigators did not have access to the roster of all visitors to these facilities holding the fitness classes, therefore contacts and cases may have been missed.
This study highlights the risks for transmission in indoor, crowded spaces with longer duration of close contact (~50 minutes) during exercise.
This review was posted on: 4 July 2020