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Coronavirus may be detectable before symptoms start, report suggests

It's still unclear at what point a person with the virus can spread it to others.
Image: COVID-19
A scanning electron microscope image shows the novel coronavirus isolated from a patient in the U.S., emerging from the surfaces of cells (green) cultured in the lab.NIAID-RML

Tests can detect the new coronavirus in people before they show symptoms, though it's still unclear whether a person can spread it to others at this point, while they are asymptomatic, a study published Tuesday says.

The new report in the New England Journal of Medicine looked at 126 people from Germany who were quarantined after being evacuated from Hubei province, the center of the coronavirus outbreak in China.

Just two of those people tested positive for the virus; neither had shown symptoms.

"We discovered that shedding of potentially infectious virus may occur in persons who have no fever and no signs or only minor signs of infection," the authors wrote.

But testing positive for the infection doesn't necessarily mean a person is contagious.

It only means the "virus is alive, capable of dividing and infecting cells," Dr. Gregory Poland, an infectious diseases expert and director of the Mayo Clinic's Vaccine Research Group in Rochester, Minnesota, told NBC News.

It does not tell you whether that person carries enough virus to be able to infect others, Poland added.

Other outside experts agreed.

Full coverage of the coronavirus outbreak

"Given that none of the other passengers [from the evacuation flight] appears to have become ill, the risk must be small," Dr. Bruce Ribner, medical director of Emory University Hospital's Serious Communicable Diseases Unit, wrote in an email.

"This is further evidence of what we expect, and suspect, from upper and lower respiratory viruses," Poland said.

"People are asymptomatic with influenza infections and spread disease. This is no different," he said. "We just don't know yet how easily and commonly this happens" with the new coronavirus.

It's a question that's on the minds of public health officials as they continue to investigate how so many passengers aboard the Diamond Princess cruise ship got sick.

More than 500 people on the ship have been diagnosed with COVID-19, the illness caused by the new coronavirus.

"CDC believes the rate of new infections on board, especially among those without symptoms, represents an ongoing risk," the Centers for Disease Control and Prevention said in a statement Tuesday.

The CDC has previously said that the tests used in the U.S. may not be able to detect the coronavirus before a person started showing symptoms. Germany uses a different test than the U.S.

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