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  • On January 23rd, a family in China traveled from Wuhan to the city of Guangzhou.

  • The next day, they ate lunch at a restaurant.

  • One of them had Covid-19, but didn't feel sick yet.

  • Within a few days, other members of the family started showing symptoms.

  • And a few days after that, so did the family who was sitting at the table next to them.

  • The family at this table also got sick.

  • And researchers say this first person was the source of all these infections...

  • Even though some of them were sitting almost 14 feet away.

  • But the people eating at these tables didn't get sick.

  • Why?

  • An air conditioning unit right here kept the air flowing through this section of the restaurant.

  • It circulated the virus from this person, through the air, to these other families.

  • This story highlights something about the coronavirus

  • that most of us are just starting to understand:

  • Its ability to travel through the air.

  • And as public spaces open up, that's led to some big questions:

  • Is it safe to go to the beach?

  • What about a park?

  • And is a runner going to get you sick?

  • If we think about our actions only in terms of safe or risky, there's really only way

  • to guarantee you won't get sick or spread Covid-19:

  • Stay home, isolate yourself, and have zero contact with the outside world.

  • But maintaining that level of caution all the time isn't really possible for most of us.

  • We need food.

  • We need supplies.

  • And sometimes, we just need to take a walk.

  • So the goal in protecting yourself and others from Covid-19 isn't to eliminate risk completely --

  • it's to minimize it.

  • If this side is perpetual quarantine,

  • and this side is getting coughed on by a bunch of sick people,

  • it's about pushing yourself as reasonably close to this side as you can.

  • So let's start with going for a walk.

  • And with someone who, like me, has also felt weird about it.

  • Before I started calling up epidemiologists and talking to them about the risks,

  • I was actually pretty paranoid.

  • And then when I actually started digging into the research, I realized the risks of getting

  • Covid-19 from runners or cyclists outside is much lower than I thought.

  • Everytime we breathebut especially when we talk,

  • and especially when we cough or sneeze

  • we let out little droplets of water.

  • Some of them are pretty big and heavy, and fall to the ground quickly,

  • like little bits of spit.

  • Others are really small and much lighter, so they float farther through the air.

  • And these droplets are what's carrying the virus.

  • If a droplet floats and then evaporates, that leaves the virus out in the air

  • for some period of time.

  • And we don't yet know the amount of virus you have to be exposed to to get sick,

  • but we do know that you lower your risk by exposing yourself to less of the virus.

  • And Sigal says there's three ways to do that:

  • The first is distance.

  • So, are you six feet away from the person?

  • Duration.

  • Are you encountering this person for one second as they whiz past you,

  • or are you around them for an hour?

  • And ventilation.

  • Is there a good airflow moving around you that can disperse any viral particles?

  • Or are you in an enclosed indoor space where they're just going to stick around?

  • The difference between how air moves inside, versus outside, is huge.

  • To show that, I used this spray, which glows under a blacklight.

  • I sprayed my test subject with it both inside and outside, from 3 feet away.

  • Even though it wasn't windy, far fewer spray particles reached his shirt outside.

  • The airflow was so much better at dispersing them.

  • And being outside also has an effect on the virus itself.

  • A virus has this protective coat of moisture around it.

  • There's a lot of things acting on it. So, there's sunlight hitting it.

  • There's wind. There's rain. There's humidity.

  • And all of that can work to kind of break apart this protective coat of moisture,

  • and decay the virus.

  • A study in China looked at 318 different outbreaks of Covid-19 across the country.

  • Only one of them involved someone catching it outdoors.

  • That study hasn't been peer-reviewed, but it's consistent with everything else we know:

  • That being outside can be pretty-low risk.

  • But your interactions with other people can increase that risk.

  • If you're talking to a friend at a close distance, your risk goes up.

  • And that risk climbs the longer your conversation continues.

  • But if you're both wearing masks to stop some of those larger droplets from spreading,

  • your risk goes down.

  • Shopping at an open-air market is less risky than being inside a store.

  • But you can reduce that risk by getting in and out quickly.

  • But what about passing a heavy-breathing runner?

  • So let me take you through what would actually have to happen for a runner or cyclist outside

  • to infect you as they pass by.

  • They would have to expel enough viral particles to be able to kickstart an infection.

  • Those particles would have to travel several feet of distance;

  • withstand the pressures of wind, rain, humidity...

  • Then the particles have to actually land in your throat or your upper respiratory tract.

  • Or on your hands, which you would then use to touch your eyes, your nose or your mouth.

  • So all of that is a pretty arduous sequence to execute perfectly.

  • Going to the beach, or to a park, isn't necessarily dangerous or safe.

  • The risk can go up or down, depending on how we each behave.

  • Which means everyone has a responsibility to lower that risk for everyone else.

  • The point here is not to be cavalier when you go outside.

  • I think we all still want to be cautious, especially as some states are starting reopening.

  • Changing your behavior to limit exposure to the virus won't reduce your risk to zero.

  • But it could lower it enough, that you can breathe a little easier.

On January 23rd, a family in China traveled from Wuhan to the city of Guangzhou.

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B1 中級

コロナウイルスの屋外対屋内の広がり方 (How coronavirus spreads outdoors vs. indoors)

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    林宜悉 に公開 2021 年 01 月 14 日
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