Experts say testing serves as snapshot

Americans are being swabbed by the thousands to learn if they have covid-19, the disease caused by the novel coronavirus. They’re trying to determine their risk of contracting or spreading the virus to someone else.

Experts say testing is a vital component of controlling the outbreak, but one test result still isn’t a green light to visit vulnerable friends or family members. The nature of covid-19, the time it takes for someone to develop symptoms, and the varied ways the virus affects people make each test a snapshot in time more than a definitive answer.

“I personally wouldn’t consider a single test a license to go see my parents, who are older and would be at higher risk,” said Carl Bergstrom, a University of Washington biology professor who studies infectious diseases.

The viral swab tests, seen at drive-thru clinics across the country, tell people whether they’re infected on that particular day, said Lucy Wilson, an infectious-disease specialist and a professor at the University of Maryland Baltimore County.

It takes time for the virus to replicate to a critical mass for a swabbing test to detect it. The time this process takes varies from person to person and ranges from two to 14 days, experts say.

“The problem is this virus is a strange virus,” Bergstrom said. “The timing varies a lot in people.”

If a person were infected today and tested tomorrow, Bergstrom said, “we have every reason to believe you’re going to test negative, even though you’re infected.”

On average, people tend to show symptoms or test positive for the virus about five days after exposure, Wilson said.

“It’s just like a pregnancy test,” Wilson said. A pregnancy test can detect only certain hormones after a certain number of days or weeks, but it doesn’t mean a person’s not pregnant.

If a person starts developing symptoms of covid-19, such as a fever, sore throat or loss of smell, experts say that person should absolutely get tested. Wilson said people need to determine whether the symptoms they’re experiencing are a result of the coronavirus or are another illness — such as strep or the flu.

The Centers for Disease Control and Prevention advises anyone with symptoms to stay home and self-isolate as much as possible.

For those who have been in contact with someone who has covid-19 but don’t have any symptoms, Wilson said, they should consider 14-day self-quarantines and discuss whether to get tested with their health care providers.

As The Atlantic magazine reported last month, it’s still not clear how accurate viral tests are for people who haven’t developed symptoms. There’s a degree of uncertainty, even with a negative test result, and not a lot of data to determine exactly how early a swab test can start to detect the infection for a person showing no symptoms.

On top of all this, the rising demand for more testing has led to weeklong delays for results. An average of 685,000 people were tested per day last week, according to data collected by the Covid Tracking Project and reported by The New York Times. The White House aims to reach 1 million tests a day by the fall.

Experts say the backlog in some parts of the country makes the results useless for efforts to control the spread of the virus. Generally, people who have the virus are symptomatic for around six days, Bergstrom said. If the results take five days to come back, then there’s only so much sick people can do to protect those around them. Bergstrom added that the results become “absolutely useless” for efforts to quarantine or to trace contacts.