BALTIMORE (WJZ) — Johns Hopkins School of Public Health researchers are expressing concerns that people are testing negative for COVID-19 when they are actually infected with the virus.

Associate Professor Justin Lessler, of Johns Hopkins School of Public Health, said the study analyzed mostly tests done with nasal pharyngeal swabs.

What they found was that many of the tests that come back negative turn out to be patients who had COVID-19.


“You might test negative because you’ve just been infected and you have a tiny bit of virus in you and it hasn’t had a chance to replicate enough for the swab to get the virus out,” Lessler said.

The study by Johns Hopkins shows the chance of a false negative test is about one in five, and sometimes higher.

Researchers said the time you start showing symptoms is when you are most infectious.

For example, if you got tested the week before you started to show symptoms, you may still have had the virus, even if the test said you did not.

The harm there is that you might have been around people and spread the virus to them, thinking you were in the clear.

“If people get overconfident based on a negative test, if you have concerning symptoms and get a negative test and then don’t go to the doctor, then I think it’s a problem,” Lessler said.

The silver lining is that if you test negative and never show symptoms of carrying the disease, you might not be as dangerous to those around you.

“We don’t know for sure, but it’s likely when you test negative, you’re less likely to transmit,” Lessler said.

Scientists still think mass testing is the right move, because to little is known about the coronavirus. They said more testing is better than less testing.

“It’s important to remember the test is still extremely useful and it’s probably our best tool besides all staying at our house, as were all more than ready to stop doing that, for combatting in this,” Lessler said.

For the latest information on coronavirus go to the Maryland Health Department’s website or call 211. You can find all of WJZ’s coverage on coronavirus in Maryland here.

Rachael Cardin