Do runners leave wake of coronavirus droplets? Simulation shows outside exercisers should keep greater distance

Warm weather in Cleveland in January

Joggers and dog walkers around the Cleveland area dressed for the warm temperatures on Saturday, January 11, 2020, as they ventured out. A jogger runs through along the path near MLK Blvd. in Cleveland. David Petkiewicz, cleveland.comDavid Petkiewicz, cleveland.com

CLEVELAND, Ohio -- A new simulation from a Belgian research team is spreading across social media, showing that joggers or bikers could be spewing coronavirus all over the sidewalk.

The simulation shows respiratory droplets flying from a runner’s mouth onto a person six feet behind, worrying people who pass others while exercising outside.

The simulation is based on the idea of a “slipstream,” used by elite athletes to boost their pace by following closely behind each other. The research asserts that people slowly walking behind other walkers can be affected by the slipstream, with the simulation showing a droplet cloud existing when someone walks 2.5 miles an hour.

Cleveland Clinic pulmonologist Dr. Humberto Choi said the theory could have some weight.

“It’s possible,” he said. “Anyone who exercises, runs or bikes, (knows) that you are breathing heavier. And if you’re running right behind someone, and that person coughs hard or sneezes, you might be in contact with those droplets. And to avoid that you just need to keep a longer distance.”

Running and exercising outside is still permitted under Ohio’s coronavirus stay-at-home order, but Gov. Mike DeWine and park officials have repeatedly reminded people to stay at least six feet away from each other. The Cleveland Metroparks closed several roads to widen routes for walkers and bikers.

The computer simulation uses principles of engineering, but the researchers have not done a scientific study on their claims. They spoke to the media before they completed a study or had peer scientists review their work.

Lead researcher Bert Blocken tweeted that people should still exercise outside, but avoid slipstreams. He recommends a distance of about 13 feet for walkers behind other people, with increasing amounts for runners.

Choi said it’s still safe to walk or exercise outside, and that droplets can evaporate very quickly. The problem would be if the person behind walks through the cloud before it’s evaporated. The simulation showed walking side-by-side or staggered diagonally at a safe distance could avoid the clouds.

Even a runner passing by theoretically wouldn’t pose as much of a threat, because you’re not directly behind them, Choi said.

The simulation did not clearly define how much of the virus that could be transmitted this way, and whether that amount could infect someone.

“On the epidemiology side – where the droplets are is much less relevant than the amount of transmission that occurs via this route. And [there is no analysis in the paper of] viral load,” Dr. Bill Hanage, associate professor at Harvard’s Center for Communicable Disease Dynamics, told The Independent. "Advice on physical distancing is really about reducing the risk of transmission rather than eliminating it altogether.”

Researchers still don’t know how temperature, humidity, wind and UV rays would affect the virus. A study published in the New England Journal of Medicine, found that the virus could remain aerosolized for 3 hours.

Researchers in a laboratory used a nebulizer to convert a liquid version of the virus into a fine spray, as part of that study. Although some hospital situations, such as intubating a patient, could also create a similar effect, doctors don’t think the virus can get into the air in normal settings.

Other studies have debated how the virus travels through the air. Humidity -- water in the air -- could slow the spread of influenza.

A China study collected air samples from public areas in Wuhan, China, but only found significant amounts of the virus in air outside of the entrance to a department store.