During 24 days in February and March, 112 people were infected with the Covid-19 virus in South Korea after participating in or associating with participants in Zumba classes, according to a sobering new epidemiological study published in Emerging Infectious Diseases.
The study, which traces the start of the illness cluster back to a one-day instructor workshop held in mid-February, raises crucial questions about the risks of infection during group exercise classes and whether and how such workouts might be made safer.
Across the country, fitness facilities are reopening now after lengthy closures because of the coronavirus, prompting some predictable concerns among members about safety. Recently, I wrote about ways to minimize infection risks at gyms if you are weight training or using exercise machines, like treadmills.
But, by their nature, group exercise classes could present unique and daunting challenges to infection control, as the new South Korean investigation suggests. In that study, epidemiologists affiliated with Dankook University College of Medicine in Cheonan report that they became aware in late February of a new, confirmed coronavirus case in Cheonan, a populous city about 50 miles south of Seoul, the nation’s capital.
By tracing that person’s contacts and following up on other newly confirmed cases in the city, the researchers discovered that the common thread connecting the infections was Zumba. Popular in South Korea, these fast-paced dance classes are prolonged — lasting for close to an hour — often crowded and punctuated by instructors’ shouts and participants’ heavy breathing.
Digging farther, the scientists tracked the earliest, precipitating coronavirus cases to a Zumba instructor-training course held on Feb. 15 in Cheonan. Of the 27 newly minted Zumba teachers attending, eight later tested positive. But in the meantime, they taught classes, without wearing masks and, in a few instances, while coughing.
Within about a week of participating, 54 of their 217 students tested positive, for an “attack rate” of about 25 percent. (An attack rate represents the percentage of people exposed who become infected.) Soon afterward, more than a dozen of the students’ and teachers’ family, friends and acquaintances also tested positive. All told, 112 cases were traced to indoor dance classes at 12 different gyms. Most of the resulting illnesses were not severe, but some led to pneumonia.
“It is thought that hyperventilation caused by severe exercise in a confined space may be the reason for the extremely high attack rate,” says Dr. Ji-Young Rhee, a professor at Dankook University College of Medicine and senior author of the new study.
But if those findings sound concerning, the data did contain some bright spots. The epidemiologists uncovered zero cases resulting from classes with fewer than five students per session or from low-intensity yoga or Pilates classes, even if they were taught by an infected instructor.
Over all, the study offers both cautions and guidance for anyone considering an in-person return to dance, yoga, boot-camp or similar group exercise classes, both the authors and other experts agree. “Exercising in a gym will make you vulnerable to infectious disease,” Dr. Rhee says. But limiting class sizes and sticking with low-intensity exercise, which entails little heavy respiration, might help to lessen viral transmission.
Proper air circulation also is essential, says Linsey Marr, a professor of civil and environmental engineering at Virginia Tech University, who studies airflow. She was not involved with the South Korean study but read it at my request. “I have actually thought about this issue a lot,” she says, “because I’m an avid CrossFitter and I want to get back to my routine. But I think indoor exercise classes can be conducted safely only if there is sufficient ventilation with outdoor air, not recirculated air.”
Frequently Asked Questions and Advice
Updated June 2, 2020
Will protests set off a second viral wave of coronavirus?
Mass protests against police brutality that have brought thousands of people onto the streets in cities across America are raising the specter of new coronavirus outbreaks, prompting political leaders, physicians and public health experts to warn that the crowds could cause a surge in cases. While many political leaders affirmed the right of protesters to express themselves, they urged the demonstrators to wear face masks and maintain social distancing, both to protect themselves and to prevent further community spread of the virus. Some infectious disease experts were reassured by the fact that the protests were held outdoors, saying the open air settings could mitigate the risk of transmission.
How do we start exercising again without hurting ourselves after months of lockdown?
Exercise researchers and physicians have some blunt advice for those of us aiming to return to regular exercise now: Start slowly and then rev up your workouts, also slowly. American adults tended to be about 12 percent less active after the stay-at-home mandates began in March than they were in January. But there are steps you can take to ease your way back into regular exercise safely. First, “start at no more than 50 percent of the exercise you were doing before Covid,” says Dr. Monica Rho, the chief of musculoskeletal medicine at the Shirley Ryan AbilityLab in Chicago. Thread in some preparatory squats, too, she advises. “When you haven’t been exercising, you lose muscle mass.” Expect some muscle twinges after these preliminary, post-lockdown sessions, especially a day or two later. But sudden or increasing pain during exercise is a clarion call to stop and return home.
My state is reopening. Is it safe to go out?
States are reopening bit by bit. This means that more public spaces are available for use and more and more businesses are being allowed to open again. The federal government is largely leaving the decision up to states, and some state leaders are leaving the decision up to local authorities. Even if you aren’t being told to stay at home, it’s still a good idea to limit trips outside and your interaction with other people.
What’s the risk of catching coronavirus from a surface?
Touching contaminated objects and then infecting ourselves with the germs is not typically how the virus spreads. But it can happen. A number of studies of flu, rhinovirus, coronavirus and other microbes have shown that respiratory illnesses, including the new coronavirus, can spread by touching contaminated surfaces, particularly in places like day care centers, offices and hospitals. But a long chain of events has to happen for the disease to spread that way. The best way to protect yourself from coronavirus — whether it’s surface transmission or close human contact — is still social distancing, washing your hands, not touching your face and wearing masks.
What are the symptoms of coronavirus?
Common symptoms include fever, a dry cough, fatigue and difficulty breathing or shortness of breath. Some of these symptoms overlap with those of the flu, making detection difficult, but runny noses and stuffy sinuses are less common. The C.D.C. has also added chills, muscle pain, sore throat, headache and a new loss of the sense of taste or smell as symptoms to look out for. Most people fall ill five to seven days after exposure, but symptoms may appear in as few as two days or as many as 14 days.
How can I protect myself while flying?
If air travel is unavoidable, there are some steps you can take to protect yourself. Most important: Wash your hands often, and stop touching your face. If possible, choose a window seat. A study from Emory University found that during flu season, the safest place to sit on a plane is by a window, as people sitting in window seats had less contact with potentially sick people. Disinfect hard surfaces. When you get to your seat and your hands are clean, use disinfecting wipes to clean the hard surfaces at your seat like the head and arm rest, the seatbelt buckle, the remote, screen, seat back pocket and the tray table. If the seat is hard and nonporous or leather or pleather, you can wipe that down, too. (Using wipes on upholstered seats could lead to a wet seat and spreading of germs rather than killing them.)
How many people have lost their jobs due to coronavirus in the U.S.?
More than 40 million people — the equivalent of 1 in 4 U.S. workers — have filed for unemployment benefits since the pandemic took hold. One in five who were working in February reported losing a job or being furloughed in March or the beginning of April, data from a Federal Reserve survey released on May 14 showed, and that pain was highly concentrated among low earners. Fully 39 percent of former workers living in a household earning $40,000 or less lost work, compared with 13 percent in those making more than $100,000, a Fed official said.
How do I take my temperature?
Taking one’s temperature to look for signs of fever is not as easy as it sounds, as “normal” temperature numbers can vary, but generally, keep an eye out for a temperature of 100.5 degrees Fahrenheit or higher. If you don’t have a thermometer (they can be pricey these days), there are other ways to figure out if you have a fever, or are at risk of Covid-19 complications.
Should I wear a mask?
The C.D.C. has recommended that all Americans wear cloth masks if they go out in public. This is a shift in federal guidance reflecting new concerns that the coronavirus is being spread by infected people who have no symptoms. Until now, the C.D.C., like the W.H.O., has advised that ordinary people don’t need to wear masks unless they are sick and coughing. Part of the reason was to preserve medical-grade masks for health care workers who desperately need them at a time when they are in continuously short supply. Masks don’t replace hand washing and social distancing.
What should I do if I feel sick?
If you’ve been exposed to the coronavirus or think you have, and have a fever or symptoms like a cough or difficulty breathing, call a doctor. They should give you advice on whether you should be tested, how to get tested, and how to seek medical treatment without potentially infecting or exposing others.
How do I get tested?
If you’re sick and you think you’ve been exposed to the new coronavirus, the C.D.C. recommends that you call your healthcare provider and explain your symptoms and fears. They will decide if you need to be tested. Keep in mind that there’s a chance — because of a lack of testing kits or because you’re asymptomatic, for instance — you won’t be able to get tested.
To reduce infection risks from airborne virus particles, she says, the current recommendation for airflow calls for about 10 liters of outdoor air per second, per person in the room. In practice, the more people in an exercise class, the more outside air needs to be flowing in and out. If you are returning to the gym or workout studio, ask your facility’s manager about their ventilation system. If the air-conditioning system does not draw in air from outside, request that the staff open all available windows and doors.
Social distancing remains necessary, too, which means class sizes almost certainly will need to be smaller than they might have been in the past. “Relatively large numbers of participants, all breathing heavily in a small space, provides ideal conditions for viral spread,” says Alexandro Andrade, a professor of exercise science at the State University of Santa Catarina in Brazil, who studies the effects of air quality on health and physical performance.
Masks or other facial coverings are likely to be required during classes, depending on local regulations or facility rules, and should be encouraged everywhere, Dr. Andrade says.
Moving group classes outside, too, if possible and practical, could bolster natural air flow, widen interpersonal spacing and drench the class in sunlight, he says. But avoid outdoor classes if they are conducted between high walls or buildings, since those bulwarks prevent the breeze from dispersing people’s expired breaths.