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May 20 2020 - Patients who had the coronavirus and recovered but tested positive weeks later probably aren’t contagious or capable of transmitting the virus, researchers in South Korea reported on Monday.

Scientists at the Korean Centers for Disease Control and Prevention studied 285 of the 447 COVID-19 patients who tested positive again after their first bout of the illness and previous negative tests. Virus samples from the “re-positive” patients couldn’t be grown in cultures in a lab, which means the patients had non-infectious or “dead” virus particles, the researchers said.

They also traced 790 contacts from the 285 cases, and so far, haven’t identified any new infections based on the re-positive cases alone. Three of the 790 contacts tested positive, but they had contact with another positive case, such as a family member. Those three also had antibodies.

The findings provide hope and a positive sign as countries begin to reopen and remove stay-at-home guidelines, Bloomberg News reported. This new report means that patients who have recovered from COVID-19 likely can’t spread the coronavirus to others.

In April, researchers found that diagnostic nucleic acid tests being used for the virus can’t tell the difference between “live” and “dead” particles, the news outlet reported, which could indicate why a recovered patient might test positive again.

The new research could also add insight about COVID-19 antibody tests, which use a blood sample to see whether someone has been exposed to the coronavirus. Scientists believe antibodies likely indicate some immunity to the virus, but they don’t know for sure or how long the immunity might last.

Based on the new findings, South Korean public health officials said people who had the virus don’t need to test negative again before returning to work or school once they’ve recovered and completed isolation.

“Under the new protocols, no additional tests are required for cases that have been discharged from isolation,” the Korean CDC said.

The agency added that it will continue to report on and study these cases and their contacts.

The percentage of cases that tested positive again seemed to vary by group and location, the researchers wrote. For instance, about a quarter of people tested positive again in schools in one city, but nearly half tested positive again in a nursing home in another city.

On average, it took about 2 weeks for patients to test positive again after being discharged and 45 days — or more than 6 weeks — after their first symptoms started. About 45% had symptoms such as a cough and sore throat when they tested positive again.

Nearly 5 million people have contracted the coronavirus worldwide, and 1.5 million cases have been confirmed in the U.S., according to data from Johns Hopkins University.

Show Sources

Korean CDC, “Findings from investigation and analysis of re-positive cases.”

Bloomberg News, “Covid Patients Testing Positive After Recovery Aren’t Infectious, Study Shows.”

Johns Hopkins University, “COVID-19 Dashboard.”

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