*How* does an asymptomatic person infect someone else with Covid 19?
March 25, 2020 8:37 AM   Subscribe

It seems that there is evidence for asymptomatic spread of Covid 19. But if someone is not coughing or sneezing, *how* can they infect someone else they are standing too close to? I am not referring to someone you live with. Just someone who is out there not even knowing they have it.
posted by uans to Health & Fitness (11 answers total) 4 users marked this as a favorite
There is a lot we don't know about this, but even perfectly healthy people cough every once in a while, probably more than you think.
posted by waffleriot at 8:42 AM on March 25 [7 favorites]

People do sneeze and cough and wipe their nose and etc. even when healthy.
posted by so fucking future at 8:44 AM on March 25 [10 favorites]

"People with mild or no symptoms can have a very high viral load in their upper respiratory tracts, meaning they can shed the virus through spitting, touching their mouths or noses and then a surface, or possibly talking. Even people who don’t feel ill occasionally cough or sneeze."

-- New Scientist, "You could be spreading the coronavirus without realizing you've got it"
posted by whisk(e)y neat at 8:46 AM on March 25 [10 favorites]

From New Scientist:

We know that coughs and sneezes spread the virus, so how is it possible for asymptomatic people to spread the infection?
People with mild or no symptoms can have a very high viral load in their upper respiratory tracts, meaning they can shed the virus through spitting, touching their mouths or noses and then a surface, or possibly talking. Even people who don’t feel ill occasionally cough or sneeze.

Once symptoms develop, a person’s viral load declines steadily, and they become increasingly less infectious. However, people appear to keep shedding the virus for around two weeks after they recover from covid-19, both in their saliva and stools (medRxiv, doi.org/dqbs). This means that even once a person’s symptoms have cleared, it may still be possible to infect other people.
Airborne droplets are likely to be the main infection route, but contaminated surfaces could play a role too. Health advice typically says the virus can persist for about 2 hours on surfaces, says William Keevil at the University of Southampton, UK.
But a study published last week suggests that this is a serious underestimate, with viable virus surviving on cardboard for 14 hours and plastic and stainless steel for up to three days (New England Journal of Medicine, doi.org/ggn88w). It can also hang around in the air for at least 3 hours.

“Survival of coronaviruses for days on touch surfaces is a hygiene risk,” says Keevil. “It is difficult to avoid touching [contaminated objects or surfaces] such as door handles and push plates, bed and stair rails, public touch screens etc.”
There is also some evidence of transmission from faeces to the mouth, says Elizabeth Halloran at the University of Washington, which reinforces the importance of handwashing.

Keevil recommends regular, rigorous handwashing or using an alcohol hand gel, and avoiding touching the eyes, nose and mouth. “The latter being extremely difficult because humans are tactile and touch their faces many times an hour,” he says.

What all this makes clear is that advising only people with a cough or fever and their families to self-isolate won’t prevent the coronavirus from spreading, thanks to its fiendish ability to cause very mild symptoms in people, and to peak in infectiousness before people even realise they are sick.
posted by Salvor Hardin at 8:47 AM on March 25 [4 favorites]

Touching their face, wiping their mouth with their hand, allergic sneezing...
posted by Tell Me No Lies at 8:47 AM on March 25 [2 favorites]

"Say it, don't spray it!" is a playground classic for a reason. It's not like fluids only leave from coughing and sneezing, and most of the vapor leaving us isn't visible droplets but misting.

That's of course on top of the fact that the human animal constantly touches our faces and everything in our environment.
posted by Drastic at 8:58 AM on March 25 [5 favorites]

People are still kissing, having sex, etc and not necessarily with close family members....I am thinking of all of those spring breakers, sharing beer cups, sweaty dancing, those kinds of things.
posted by OHenryPacey at 9:23 AM on March 25 [1 favorite]

think about the cloud of your breath on a very cold day.

we're all exhaling all the time.
posted by fingersandtoes at 9:45 AM on March 25 [13 favorites]

Here is another reference that presents the POV of the virus and an average but very unlucky victim. FWIW.
posted by forthright at 10:02 AM on March 25 [4 favorites]

How long does coronavirus survive on different surfaces? (Guardian, Mar. 25, 2020)
The New England Journal of Medicine just published a study that tested how long the virus can remain stable on different kinds of surfaces within a controlled laboratory setting. They found that it was still detectable on copper for up to four hours, on cardboard for up to 24 hours, and on plastic and steel for up to 72 hours.
> How Long Will Coronavirus Live on Surfaces or in the Air Around You? (NYT, Mar. 17, 2020)
When the virus becomes suspended in droplets smaller than 5 micrometers — known as aerosols — it can stay suspended for about a half-hour, researchers said, before drifting down and settling on surfaces where it can linger for hours. The finding on aerosol in particular is inconsistent with the World Health Organization’s position that the virus is not transported by air. [...] That the virus can survive and stay infectious in aerosols is also important for health care workers. For weeks experts have maintained that the virus is not airborne. But in fact, it can travel through the air and stay suspended for that period of about a half-hour.
posted by katra at 10:06 AM on March 25 [1 favorite]

The article linked to by forthright is amazing and well-written but fucked me up real good for a day, so be warned.
posted by kimberussell at 10:17 AM on March 25 [4 favorites]

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