"You could be spreading the coronavirus without realizing you have it!"

Graham Lawton reports in part in NewScientist,

You could be spreading the coronavirus without realizing you’ve got it

...For most people who do fall ill, symptoms are usually mild and develop slowly, according to the US Centers for Disease Control and Prevention. While many have heard that a cough, fever, shortness of breath and fatigue can be signs of covid-19, the condition’s symptoms can also include a runny or stuffy nose, sore throat, headache, muscle pain, diarrhoea, nausea and vomiting.

...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.

...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.

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