A superspreader event at a Hong Kong fitness center highlights the risk of Covid-19 transmission in confined spaces with poor ventilation, according to a study published by the US Centers for Disease Control and Prevention Tuesday.
Researchers with the University of Hong Kong studied how a trainer infected with Covid-19 was connected to 101 subsequent cases among gym visitors and 53 close contacts.
On March 10, a 27-year-old trainer at a fitness center in Hong Kong with no symptoms tested positive for Covid-19, according to the study. Since the trainer had been teaching in-person classes between February 28 and March 8, the gym was closed to the public and local health authorities began contact tracing.
About 300 people who visited the fitness center between February 25 through March 10 were required to be tested, and of those, seven staff members and 94 customers tested positive.
More than 80% of those cases were detected within three days of the trainer testing positive. The team also reported 53 close contacts of those cases tested positive for Covid-19, despite having no link to the fitness center.
Of the 102 cases connected to the gym, 46 showed no symptoms when they were tested — a much higher proportion of asymptomatic cases than in the general Hong Kong population, researchers noted. The team said it wasn’t clear why that was, although they noted the 102 cases were younger on average than the general population.
How it happened: The team used virus sequencing to determine the event had been caused by a “single virus introduction.”
Visitors to the fitness center were not required to wear masks at the time of the outbreak and the gym had poor ventilation, which researchers said may have played a major role in the outbreak.
After the outbreak, new recommendations were put in place to prevent similar outbreaks.
“Our finding highlights the risk for virus transmission in confined spaces with poor ventilation and limited public health interventions,” the researchers wrote.