There’s another part of the equation that affects your risk of contracting the coronavirus. Besides hygienic practice and social distancing, a third critical element in the formula is the time you spend in an infected environment.

One doctor summed it up as “Successful Infection = Exposure to Virus x Time.”

Dr. Erin Bromage, a comparative immunologist and professor of biology at the University of Massachusetts Dartmouth, said that while you can get the virus if an infected person coughs or sneezes nearby, you can also get sick if you are in an enclosed space for a long period of time where the virus has been released by someone just breathing into the air.

“The longer time you spend in that environment the more virus you breathe in, the more it can build up, and then establish infection,” Bromage told CNN. “So, it’s always a balance of exposure and time. If you get a high level of exposure, it’s a short time and if you have a lower level of exposure, it’s a longer time before that infection can establish.”

The expert said that’s why grocery store workers have a greater risk of contracting the virus than we do during short shopping trips. This theory has been supported by recent stories on how a single person in an enclosed space can infect dozens of others. For example, the The News Tribune reported that a COVID-19 “superspreader” infected 52 other people during a 2 ½ hour choir practice in Mount Vernon, Washington, on March 10. Two of these choir members died.

Other examples have included multiple cases of infected persons in gym and dance classes, restaurants and other establishments, says CNN. Experts say that we don’t know what the specific time frame is for exposure and contracting the virus because virus testing on humans is unethical. But the Centers for Disease Control and Prevention said on its website:

“Data are insufficient to precisely define the during of time that constitutes prolonged exposure. Recommendations vary on the length of time of exposure but 15 minutes of close exposure can be used as an operational definition.”

Bromage added that the noisier the closed environment, the riskier the situation. According to The Jerusalem Post, researchers from the National Institutes of Health found that when people speak loudly, they emit contagious particles similar to those sent into the air by a cough or sneeze.

“A single minute of loud speaking generates at least 1,000 virus-containing droplets,” the study authors said. They further stated that those droplets can remain in the air for over 8 minutes and up to 14 minutes.

That’s why South Korean researchers found that students in a tranquil yoga or Pilates class didn’t become infected with the coronavirus as frequently as those attending intense dance classes, and why the choir members were so severely infected.