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Can asymptomatic people transmit covid-19? 1:45
(CNN) - This new coronavirus is bizarre for many reasons, making its spread unpredictable and difficult to control.
A rarity is the ease with which people can be infected by someone without symptoms. But there is a difference between asymptomatic spread and presymptomatic spread.
This is what you need to know:
Asymptomatic spread is the transmission of the virus by people who have no symptoms and will never have symptoms of their infection. But those infected carriers could still make others sick.
Presymptomatic spread is the transmission of the virus by people who do not look or feel sick, but who will eventually have symptoms later.
How can I know if someone is presymptomatic or asymptomatic?
You can not. Both types of carriers look and feel normal, although presymptomatic carriers will have symptoms later.
Studies suggest that presymptomatic spread is more common than asymptomatic spread.
"Detailed tracing of contacts from Taiwan, as well as the first European broadcast network in Germany, suggested that true asymptomatics rarely transmit," said Babak Javid, principal investigator at Tsinghua University School of Medicine in Beijing and consultant of infectious diseases in Cambridge University hospitals.
"However, those (and many other) studies have found that paucisymptomatic transmission can occur, and in particular, in the German study, they found that transmission often seemed to occur before or the day the symptoms first appeared." .
READ : Asymptomatic transmission of coronavirus "appears to be rare," says a WHO official
How is it possible to spread the coronavirus without symptoms?
"When you talk, sometimes you spit a little," said Anne Rimoin, professor of epidemiology at the UCLA School of Public Health.
"You will rub your nose. You will touch your mouth. You will rub your eyes. And then you will touch other surfaces, and then you will spread the virus if you are infected and take it out. ”
How many people are infected by someone without symptoms?
The US Centers for Disease Control and Prevention. USA (CDC) estimate that 40% of coronavirus transmission occurs before people feel sick.
In a study, about 4 in 5 people with confirmed coronavirus in China were likely infected by people who didn't know they had it, according to research published in the journal Science .
"These findings explain the rapid geographic spread of the (coronavirus) and indicate that containment of this virus will be particularly difficult," the researchers wrote.
Many people with coronaviruses have no idea that they have it, either because they are asymptomatic, presymptomatic, or paucisymptomatic (who have extremely mild symptoms).
The CDC said that almost half of the 712 people with coronaviruses who were on the Diamond Princess cruise ship had no symptoms when they tested positive.
And a study from Iceland showed that 50% of those who tested positive had no symptoms at the time of the test.
How can so many people have or spread the coronavirus without symptoms (yet)?
This coronavirus has a long incubation period, the time between when someone becomes infected and when they begin to show symptoms (if they have symptoms).
Flu can also be transmitted without symptoms, but the incubation time is much shorter, usually one to four days, and symptoms often appear within two days of infection, according to the CDC.
With the coronavirus, the incubation period is about three to 14 days, and symptoms generally appear "within four to five days after exposure," according to the Harvard Medical School.
"We know that a person with covid-19 can be contagious 48 to 72 hours before they begin to experience symptoms," the Harvard experts wrote.
"Emerging research suggests that people may be more likely to transmit the virus to others in the 48 hours before they start experiencing symptoms."
Are presymptomatic carriers more contagious before or after having symptoms?
"People tend to be the most contagious before they develop symptoms, if they are going to develop symptoms," said Dr. Sanjay Gupta, chief medical correspondent for CNN.
"They call that the presymptomatic period. Therefore, people tend to have more viruses at that point apparently in the nose, in the mouth. This is even before you get sick. And they may be transmitting that virus to the environment. "
If I can't know who is presymptomatic or asymptomatic, how do I stay safe?
Wearing masks and keeping a physical distance from others "can help reduce the risk that someone infected but not yet contagious can unknowingly infect others," the Harvard team said.
CNN's Jacqueline Howard and Michael Nedelman contribute to this report.
Asymptomatic