New study on Asymptomatic People Carrying the Coronavirus in High Amounts

Of all the coronavirus’s qualities, perhaps the most surprising has been that seemingly healthy people can spread it to others. This trait has made the virus difficult to contain, and continues to challenge efforts to identify and isolate infected people.

Most of the evidence for asymptomatic spread has been based on observation (a person without symptoms nevertheless sickened others) or elimination (people became ill but could not be connected to anyone with symptoms).

A new study in South Korea, published Thursday in JAMA Internal Medicine, offers more definitive proof that people without symptoms carry just as much virus in their nose, throat and lungs as those with symptoms, and for almost as long.

“It’s important data, that’s for sure,” said Benjamin Cowling, an epidemiologist at the University of Hong Kong who was not involved in the work. “And it does confirm what we’ve suspected for a long time — that asymptomatic cases can transmit infection.”

Discussions about asymptomatic spread have been dogged by confusion about people who are “pre-symptomatic” — meaning they eventually become visibly ill — versus the truly asymptomatic, who appear healthy throughout the course of their infection.

The new study is among the first to clearly distinguish between these two groups.....