Topic: Don’t get a false sense of security with Covid-19 testing.
If you think a negative test result means you don’t have coronavirus, you could be wrong.
It can take days before a new infection shows up on a Covid-19 test.
“We know that the incubation period for Covid-19 is up to 14 days. And before that, you can be testing negative, and have no symptoms,” emergency medicine physician Dr. Leana Wen told CNN. “But you could actually be harboring the virus and be able to transmit it to others.”
So if you want to get tested as a precaution before seeing friends or family, here’s what you need to know:
If I got infected yesterday, would a test today pick that up? Probably not. A study in the medical journal Annals of Internal Medicine examined false-negative test results of people who actually had Covid-19.
The study estimated that during four days of infection before symptoms typically started, the probability of getting an incorrect/negative test result on Day 1 was 100%.
On the day people started showing symptoms, the average false-negative rate had dropped to 38%, according to the study. Three days after symptoms started, the false-negative rate dropped to 20%.
“The virus just takes time to replicate in the body to detectable levels,” said Justin Lessler, a senior author of the study and associate professor of epidemiology at the Johns Hopkins Bloomberg School of Public Health.
“You can get infected by just a few viral particles, but these will not be detectable until they have time to replicate to adequate levels to be detected,” he told CNN by email.
So how many days should a person wait after possible exposure to get tested?
“There is no hard and fast rule, but the evidence suggests getting a test before the third day after exposure is not of much use,” Lessler said.
Topic Discussed: Don’t get a false sense of security with Covid-19 testing.
