SAN FRANCISCO (KGO) -- San Francisco researchers are noticing that during the omicron surge people were testing positive for COVID-19 for longer than five days.
After a year of collecting data from more than 60,000 people getting tested in San Francisco, scientists found compelling details on how long COVID infections are lasting.
"We found that 80 percent of symptomatic people at day five were still positive. A third of symptomatic people were still positive at 10 days," said Dr. Joe DeRisi, President of the Chan Zuckerberg Biohub.
Even though the CDC recommends for people go back to work after five days of infection, Dr. DeRisi one of the lead investigators of this study says you could still be infectious even if you don't have any symptoms.
"To the best of our knowledge as long as you are testing positive by antigen test there is a high likelihood you are still infectious. Even at 10 days," said Dr. DeRisi.
Marc Morozumi, a San Francisco Yoga Instructor tested positive for 10 days even though he reported feeling normal after day four of infection.
"I woke up Wednesday morning, and I said I feel better. I took a test and still showed positive. I took a test on Friday, positive. On Sunday, positive. My friends told me 'stop taking them. Those are expensive'," said Morozumi.
Morozumi decided not to teach in-person to minimize the possibility of infecting his students.
"It was frustrating but I was talking to other friends and several friends were saying it was day 10 for them too," said Morozumi.
But why is the infection period longer than five days among 80 percent of people who were part of this study?
"We don't understand the basics of the immunology that allows one person to clear the virus faster than another," said Dr. DeRisi.
For now, Dr. DeRisi recommends going by the results of an antigen test instead of a PCR.
"Unlike PCR which checks the genetic material of the virus regardless if the virus is dead or not," said Dr. DeRisi. "Antigen tests actually test for the actual virus itself. The protein of the virus. So it more closely correlates with being infectious."
Dr. DeRisi said it will take years to truly understand why it takes longer for some people to clear the virus compared to others, but he says these are all signs that the virus continues to evolve.
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