What you need to know about how the coronavirus spreads — it’s not just about staying 6 feet apart

(Rick Egan | The Salt Lake Tribune) Walkers and runners exercise at Liberty Park, Monday, April 13, 2020.

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It’s been drilled into us in recent weeks — stay 6 feet away from people. That’s 6 feet between people in line or 6 feet away from others playing at the park.

Remember — 6 FEET!

The idea is that the droplets you release as you talk or cough will dissipate before hitting another person.

This is a good rule of thumb and we should live by it, but as with seemingly everything about this virus, it is not that easy. And knowing a bit about the nuance could help you stay safe, especially as some restrictions are eased during these summer months.

I first heard the 6-feet mantra on March 11. That’s when Utah Jazz center Rudy Gobert — and the world — found out that he had tested positive. Within a few hours, the state of Oklahoma tested me and 57 others of the traveling Jazz party for COVID-19.

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Oklahoma state epidemiologist Laurence Burnsed then told us we were at significant risk of being infected if we had had sustained close contact with Gobert — defined as being within 6 feet for 15 minutes or more. Utah state epidemiologist Angela Dunn told us the same thing the next day.

Those who had close contact were asked to self-quarantine for 14 days, but for those who hadn’t, the quarantine was optional.

Naturally, I racked my brain. I was at a news conference with Gobert after the prior game. I was about 6 feet away, but was it more like five feet or seven? I spoke to Donovan Mitchell — who also tested positive — the morning before the game from about that same distance for seven minutes. And then I spoke briefly to him afterward. Did all of that add up to 15 minutes?

Out of an abundance of caution, I decided to self-quarantine. I never developed symptoms.

I’m glad I made that decision. Because in the six weeks since, we’ve learned that transmission of the coronavirus happens in some weird ways, outside of the 6-feet and 15-minute window. As we begin to open businesses and the economy, there are factors people should be aware of as they make decisions about the “new normal.”

Take this restaurant study released this week. In January, a family traveled from Wuhan, China, to Guangzhou, and had lunch at a third-floor restaurant. One member of the family, labeled A1 in the figure below, had COVID-19 but had not yet experienced any symptoms. There were 91 people in the restaurant at the time, and 10 got the disease. The restaurant was the only known source of exposure for all 10. Here’s the map of where they were sitting:

Restaurant goers catch COVID-19 from one infected patient at a nearby table. (https://wwwnc.cdc.gov/eid/article/26/7/20-0764-f1)

The two people to Patient Zero’s left didn’t get it, but the two people to her right did. People at tables B and C got the virus from further than 6 feet away, but not people at tables D, E, and F, even though some were closer. It’s a little bit crazy, right?

The study’s authors hypothesize that the air conditioner could explain the flow of small infected droplets suspended in midair, both in the direction of table B behind her (the direction of airflow) and table C in the opposite direction as the air circulated.

But that no other tables in the whole restaurant had any cases indicates that the small droplets probably didn’t spread much throughout the dining room: They stayed pretty close to the air conditioner’s flow. That’s something to consider as restaurant rules are put together in Utah.

Here’s another example: 293 Buddhists went to a worship event held in a temple in January in China. One bus had 67 people on it — including one person who had been exposed to residents from Wuhan. She was the only one of all 293 people to be exposed, and was asymptomatic during the trip, though started to feel worse the evening after returning.

The bus ride was 50 minutes one-way, or 100 minutes round trip. All bus passengers stayed in their same seats for both legs of the trip, and the bus had its air conditioners on, but set to indoor-recirculation mode rather than getting air from outside. The air conditioning vents were below the windows, and only four of the windows were openable.

On this bus, 24 people caught the virus. Another bus making the same trip to the temple ended with zero cases. In addition, seven more people at the temple who didn’t ride in either bus got the disease — all of whom reported close contact with Patient Zero, labeled as IP below in Row 8. Here’s where the sick people sat in the bus:

A bus of Buddhists catches the coronavirus. (https://www.researchgate.net/publication/340418430_Airborne_transmission_of_COVID-19_epidemiologic_evidence_from_two_outbreak_investigations)

Again: very strange! First, they found no correlation between distance from Patient Zero and whether someone got the disease. Again, you may want to blame air conditioning, but in this case, only one person next to a window vent on the left side of the bus caught the virus — the one sitting next to Patient Zero. Small droplets that hang in the air are the most likely explanation.

But if the coronavirus were always as contagious as it was on this bus or in that restaurant, we’d all already have it right now. I mean, think of Gobert: of all of the players, coaches, staff, media and more who fly on the Jazz’s team plane, or spend time with him in the locker room and on the bench, only one tested positive.

In fact, it even spreads within households way less frequently than you’d expect. Three studies (one in the U.S., one in Korea, and one in Wuhan) have looked at how often people living in the same household get COVID-19 after one person tests positive. The three studies found rates between 7.5% and 15%. In other words, the majority of people with a sick family member in the house don’t seem to get the disease.

That’s a known property of COVID-19: that there are some super spreaders and huge swaths of people who don’t seem very contagious at all. In fact, 80% of coronavirus cases come from 10% of the spreaders, according to this study of the data.

We’ve talked a lot about contagion rate in these articles — the number of people each sick person infects on average. Right now, estimates for coronavirus’ base contagion rate are somewhere between 2.5 and 6. But, in truth, that average is reflective of the fact that for every one person who gives the disease to 20 people, there are 10 who give it to one person or nobody at all.

That doesn’t seem to be unusual for coronaviruses in general, so we can use some of the research on SARS and MERS as we try to understand what’s going on.

Unfortunately, we have no idea what makes a person more likely to be a super spreader or some event more likely to be a super-spreading event.

It could just be random luck: someone showing up at a crowded place exactly when they’re most contagious. For example, two studies on airline flights were done in the wake of SARS. One found 17% transmission on a four-hour flight, while the other found 3% transmission on a 14-hour flight.

There are breadcrumbs to track. For example, singing or raising your voice seems to be somewhat dangerous. The most famous example is the Washington State choir, where 60 singers showed up and 45 left with the virus. “Amen”-shouting churches, hymn-singing funerals, and drunkenly singing bars have all been the sites of super-spreader events, as this Vanity Fair article pointed out.

In fact, one 2019 study found that “saying ‘aah’ for 30 seconds releases more micron-scale particles than does 30 seconds of coughing.” Do it loudly? More particles. But there have certainly been quiet gatherings where the virus has super-spread too, so it’s not a wholly explanatory theory.

The good news? Outside seems pretty safe if distance is maintained.

In one study of 7,324 cases in China, only once was the virus spread outside: A man returning from Wuhan had a conversation with a 27-year-old in Shangqiu, who had symptoms a week later. That spread seems likely to have been by larger droplets direct from person to person, rather than smaller ones suspended in midair — it seems those break up quickly outside.

Speaking of outdoors, weather will impact the virus as well. One look at the issue tracked how transmission changed as the weather got warmer and cooler. The study’s authors estimated that transmission will fall by 43% between March and June 2020 for countries in the Northern Hemisphere due to the warmer weather. That’s not enough to eliminate the virus during the summer, but it does seem the sun will give us a boost.

In sum, this kind of research should give decision-makers in both the public and private sector significant information on how to structure restrictions moving forward. With asymptomatic transmission being so widespread, being careful in all sorts of situations remains the name of the game.

And for individuals, maybe you should not get close to singers or loud talkers. When the restaurants start opening up, get an outside table if you can.

Andy Larsen is a Tribune sports reporter who covers the Utah Jazz. During this crisis, he has been assigned to dig into the numbers surrounding the coronavirus. You can reach Andy at alarsen@sltrib.com or on Twitter at @andyblarsen.