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  • A new study found 13 percent of their 176 participants still showed “clinically relevant” levels of live virus after 10 days.
  • Experts say that everyone is different in their ability to clear a virus from the body.
  • The study’s findings may undercut current CDC guidelines.

Researchers in the U.K. used a newly adapted test to find that some people who contract SARS-CoV-2, the virus that causes COVID-19, could still transmit the virus to others — even after a 10-day quarantine.

The test detects levels of live virus and was used for people confirmed to have COVID-19 using a conventional PCR test.

Out of the 176 participants, findings found that 13 percent still showed “clinically relevant” levels of live virus after 10 days, with some showing significant levels for up to 68 days.

“The test works by detecting a piece of the COVID-19 virus that is only present when the virus is dividing and therefore potentially active,” Professor Lorna Harries, PhD, of the University of Exeter Medical School, who oversaw the study, told Healthline.

The study was published today in the International Journal of Infectious Diseases.

“The PCR test amplifies and then replicates the RNA from the virus — in other words, it detects if genetic material from the COVID virus is present in your sample,” said Dr. Robert G. Lahita, director of the Institute for Autoimmune and Rheumatic Disease at Saint Joseph Health, and author of “Immunity Strong.”

He emphasized that the PCR test is the “gold standard” of tests for figuring out whether someone is positive for COVID-19, and is the most accurate.

Harries explained the test used for this study works under exactly the same conditions as conventional PCR tests, and “can be used on the same clinical sample as is being taken routinely.”

She confirmed that the details of the test are now published, for use by anyone.

“Our local hospital had noticed that they were still seeing high levels of infection in staff and patients during the first wave of COVID despite following strict isolation rules,” said Harries.

“So the question was whether there were people who were still infectious after 10 days,” she continued.

According to Harries, the findings weren’t entirely surprising. She pointed out that “everyone is different,” and it’s expected that individuals will vary in their ability to clear the virus.

“But we were surprised, and a little worried, by how many people still had high levels of potentially infectious virus after 10 days,” she admitted. “At 7 days, it is about 1 in 5, and at 5 days 1 in 3 according to our data.”

Lead study author Merlin Davies, a PhD student at the University of Exeter Medical School, said in a statement that in some work settings it may make sense to require people to test for active virus before returning to work.

He also said they want to conduct larger trials.

According to Lahita, detecting clinically relevant levels of virus after quarantine is a significant finding in light of current Centers for Disease Control and Prevention (CDC) guidelines.

“Right now, the CDC is saying people can stop isolating after 5 days if they wear a mask for the following 5 days, and after 10 they are good to go,” he pointed out.

“Because of the findings of this study, the data essentially fly in the face of the current CDC guidelines — for some individuals,” Lahita continued.

He also said that we need to keep in mind that the study only indicated 1 in 10, and not 100 percent of people, were found to carry live virus.

According to Lahita, CDC guidelines still reduce transmission risk.

“Without a quarantine period, people would infect numerous others by going out while sick on their most contagious days,” he said.

However, he noted that based on these data, he suspects some people are still infectious after 10 days even if they don’t have symptoms.

“These data indicate that the CDC should reassess their guidelines,” said Lahita. “The current quarantine may not be adequate for everyone and supports the fact that we should continue mask wearing in close spaces, particularly if someone has recently recovered from COVID.”

“We don’t really know at this point,” said Lahita.

He added that although we know how long the virus can remain present in the body, we still can’t accurately determine how long any particular individual is infectious.

“We are learning more about COVID and its variants each week as scientists conduct additional research,” he continued. “The virus can be found in tissue even over 200 days out.”

Researchers tested people with COVID-19 for live virus after a 10-day quarantine and found that 1 in 10 still carried the live virus, potentially posing a significant risk of transmission.

Experts say that people can vary widely in their ability to clear viruses from their bodies, and in settings with vulnerable populations, this could present a serious health risk.

They also say that current CDC guidelines should be reassessed in light of these findings.