You're most likely to catch the coronavirus in a poorly ventilated space. That makes offices very risky.

• The coronavirus typically spreads via droplets from an infected person.
• A majority of coronavirus infections occur indoors when people are in sustained proximity to someone sick.
• This suggests that parks are low-risk spaces, while offices, prisons, and nursing homes are not.
• Experts recommend increasing air flow in potentially crowded, indoor spaces to lower infection risk. But employees might never return to office life as it was.
• Visit Business Insider's homepage for more stories.

We are all becoming accustomed to a constant internal monologue about minimizing our risk of coronavirus infection: "Is it safe to go running?" "Should I dash into the pharmacy?" "How close is too close to stand in line?"

Scientists agree that the virus primarily spreads between people via droplets that fly through the air when an infected person coughs, sneezes, or speaks. Evidence also increasingly shows that the risk of infection is much higher in poorly ventilated, crowded areas.

So while it can be jarring to have a runner invade your 6-foot bubble, that fleeting moment is far less risky than, say, working in an office with hundreds of colleagues.

A recent study about an outbreak in a call center in Seoul, South Korea, revealed that almost half the employees on one floor got infected. Nearly all of them sat in the same section.

That makes the prospect of returning to offices challenging — and scary.

The coronavirus primarily spreads indoors

The more time you spend near someone who has COVID-19, the higher the chance their infectious droplets make it over to your face.

"I would not worry about walking by someone," Dr. Amesh Adalja, an infectious-disease specialist at Johns Hopkins University, told Slate. "Even in a healthcare setting, contact is defined by being near someone for a certain amount of time. I would not worry about these fleeting encounters."

Airflow matters, too.

According to William Schaffner, a professor of infectious diseases at Vanderbilt University, coronavirus particles could more easily linger in the air in a small space like an elevator.

"In such a tightly enclosed space without vigorous air movement for a short period of time, I'm afraid you might be exposed," Schaffner previously told Business Insider.

The same goes for hospitals. A study published last week in the journal Nature found that virus particles were most highly concentrated in the air within the 9-square-foot toilet areas in patients' rooms in two hospitals in Wuhan, China. These toilets were not ventilated.

In ventilated ward areas, however, the amount of virus was very low, a difference the authors attributed to proper air circulation.

It's not surprising, then, that most coronavirus transmission occurs indoors.

A preliminary report from Japanese scientists (which has yet to be peer-reviewed) suggested that the odds an infected person "transmitted COVID-19 in a closed environment was 18.7 times greater compared to an open-air environment." Another pre-print study examined 318 outbreaks in China that involved three or more cases, and found that all but one involved the virus jumping between people indoors.

"The general principle should be: Outside is better than inside; open is better than closed; fewer is better than more people; and stay away from sick people," Dr. Erich Anderer, a neurosurgeon and founding member of the North Brooklyn Runners group, previously told Insider.

Restaurants, prisons, meat-processing facilities, and nursing homes are all high-risk

The worst coronavirus clusters around the US are all tied to spaces that force people into close quarters for extended periods of time. According to a live-updating New York Times page that tracks outbreaks around the country, all but one of the 12 hardest-hit US locations were prisons, jails, and meat-processing facilities. Multiple nursing homes are also high on the list.

Restaurants, too, can be risky. In a recent research letter in the journal Emerging Infectious Diseases, scientists described how nine people sitting more than 3 feet apart at a restaurant in China got the coronavirus in January. The virus likely spread because of the restaurant's air-conditioner, they noted.

The authors advised restaurants to increase the distance between tables, improve ventilation, and cap how long diners can sit.

The same guidance should probably then apply to office settings as well.

The call-center outbreak in Seoul provided a clear case study of office transmission: Of the center's 811 employees, 97 got sick. Of those 97, all but three sat on the same floor, and 79 were in the same section.

"Despite considerable interaction between workers on different floors of building X in the elevators and lobby, spread of COVID-19 was limited almost exclusively to the 11th floor, which indicates that the duration of interaction (or contact) was likely the main facilitator for further spreading," the Korean CDC wrote in its report about the outbreak.

Companies may rethink how they resume office life

According to a recent report from the University of Minnesota's Center for Infectious Disease Research and Policy, the coronavirus pandemic could last up to two years. Waves of COVID-19 infections will likely continue until a majority of the human population becomes immune or a vaccine is developed.

Given that the risk of infection will loom for a long time, employers will be forced to adapt.

"Staggered shifts, enforced flextime, and 24/7 operations may become the norm, along with working remotely," Rachel Morrison, a professor of work psychology at the Auckland University of Technology, wrote in The Conversation.

Some CEOs have already cottoned onto that reality.

Jes Staley, chief executive of Barclays, told reporters on Wednesday that his company is reevaluating how much it needs office space at its London headquarters and branches.

"There will be a long-term adjustment to our location strategy," Staley said, adding, "the notion of putting 7,000 people in the building may be a thing of the past."