More than 100 infections linked to fitness classes in South Korea

More than 100 coronavirus infections in South Korea have been linked to a fitness instructor workshop from mid-February, researchers have found.

The infections aren’t recent — they were all identified by March 9 — but the new research offers insight into how rapidly coronavirus can spread in enclosed spaces.

What happened: Almost 30 instructors participated in the original workshop, which was held in Cheonan, South Korea. They trained intensely for four hours, and while none had symptoms at the time, eight instructors eventually tested positive for the virus.

More cases uncovered: Less than a month later, researchers had identified 112 coronavirus cases linked to dance classes in a dozen different facilities. Half of the cases were the result of direct transmission from instructors to students, and some people went on to infect others outside of class. 

Why did the virus spread this way? Several factors may have made it easier for the virus to spread, according to Sukbin Jang and colleagues at the Dankook University College of Medicine in Cheonan. They published their findings in Emerging Infectious Diseases, a journal from the US Centers for Disease Control and Prevention.

“The moist, warm atmosphere in a sports facility coupled with turbulent air flow generated by intense physical exercise can cause more dense transmission of isolated droplets,” they wrote.

Classes linked to transmission had five to 22 students and took place in small spaces for almost an hour. Out of 217 students exposed to infected instructors, 57 of them — about one in four — ended up testing positive.