Why do people test negative and then positive for COVID-19?

Published: Jan. 19, 2022 at 6:59 PM CST
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HUNTSVILLE, Ala. (WAFF) - There’s a good chance that you know someone across the Tennessee Valley who has tested negative for COVID-19 and then tested positive.

Lisa Apgar experienced that with her daughter.

“The home test was negative so I thought, well I could probably send you to school. The home test is negative. I know they’re not 100 percent but I could probably send you, but she was just feeling really sick,” said Apgar.

It would become clear just a few days later after taking a PCR test.

You may be wondering why this is happening. Dr. Karen Landers with the Alabama Department of Public Health says the common reason is people may be testing too soon or too late.

“A lot of this depends on the individual tests, the types of tests that a person uses and the timing of the tests in terms of when the person develops an illness and when they develop symptoms,” said Dr. Landers.

UAB infectious diseases physician, Rachael Lee, says quote: “If you are without symptoms, it is best to wait 3-5 days after exposure to someone with COVID-19 for the best results from a COVID test. It takes time for the virus to build up to a point where it can be diagnosed by a COVID test, so testing too soon after exposure may not capture the presence of the virus.”

Dr. Landers said there’s a tradeoff when using at-home tests vs PCR tests.

“The antigen test is really a test that after several days may not likely remain positive because it’s actually checking for a different protein. Whereas, the PCR, being the gold standard, actually may remain positive for several weeks,” said Dr. Landers.

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