They found evidence that a single and intense dance workshop led to the diffusion of Covid-19 to 112 different people.
The infections are not recent – the lesson was held in February and all cases were identified by March 9 – but new research offers information on how quickly coronavirus can spread in enclosed spaces.
Nearly 30 instructors attended the original workshop, held in Cheonan, South Korea. They trained intensively for four hours and, while none had symptoms at the time, eight instructors eventually proved positive for the virus.
“By March 9, we identified 112 Covid-19 cases associated with fitness dance classes in 12 different sports facilities in Cheonan,” they wrote.
Half of the cases were the result of direct transmission from instructors to students and some people continued to infect others outside the classroom.
“The instructors and students met only during the lessons, which lasted 50 minutes twice a week and had no contact outside the lessons. On average, the students developed symptoms 3.5 days after participating in a fitness dance lesson, “wrote the Dankook team.
Packed and sweaty classes
“Before the sports facilities closed, a total of 217 students were exposed in 12 facilities, with an attack rate of 26.3%,” they added.
“Fitness dance lessons set in Latin rhythms have gained popularity in South Korea due to high aerobic intensity.” The team specifically referred to Zumba classes, a dance class characterized by energetic music and densely crowded rooms.
A number of factors may have made the spread of the virus easier, according to Sukbin Jang and colleagues at Dankook.
“The warm and humid atmosphere in a sports facility combined with the turbulent airflow generated by intense exercise can cause a denser transmission of isolated droplets,” they wrote.
The lessons connected to the broadcast had from 5 to 22 students and took place in confined spaces for almost an hour. No cases were observed in classes with less than five participants.
One of the instructors, however, has taught Pilates and yoga – and none of his students have contracted the virus. “We hypothesize that the lower intensity of Pilates and Yoga did not cause the same transmission effects as those of the more intense fitness dance lessons,” said the researchers.
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