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Cluster of Coronavirus Disease Associated with Fitness Dance Classes, South Korea

Our take —

This study identified a cluster of 112 total COVID-19 cases traced back to a fitness dance workshop for instructors that occurred February 15th. Of the 27 instructors who attended, 8 (30%) tested positive. Of subsequent onward transmission from instructors to others, most was to students that instructors taught after becoming infected (n=57, 51%). It is possible that some contacts were missed, however, due to incomplete records of visitors to the fitness facilities. This study highlighted the risk for transmission during exercise classes in indoor, crowded spaces.

Study design

Case Series

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%).

Study Strengths

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.

Value added

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