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June 1, 2022

Some people test positive for Covid-19 for weeks. Are they still infectious?

Daily Briefing

    After contracting Covid-19, some people may continue to test positive on rapid tests for 10 days or longer—and experts are split about whether these individuals should continue to isolate past 10 days or just employ safety precautions until they test negative.

    How long can people test positive with omicron?

    According to the New York Times, the omicron variant of the coronavirus moves quickly, with viral levels typically peaking less than five days after the virus is first detectable. However, some people will continue to test positive for the virus even up to 14 days later.

    For example, a new analysis, which has not yet been peer-reviewed, found that roughly 20% people who were repeatedly tested during the omicron wave still tested positive on rapid tests 11 days after they first became symptomatic or initially tested positive.

    "For some people, they're seeing fairly prolonged courses of being antigen-positive," said Yonatan Grad, an immunologist and infectious disease expert at the Harvard T.H. Chan School of Public Health. "I think we chalk it up to some variation in people's immune system and ability to respond to infection and clear this virus."

    However, a positive test may not always mean that an individual is still infectious. "Some people may not be infectious at the end of their course even if still antigen-positive, whereas others may be infectious even if antigen-negative," Grad said.

    According to research from Amy Barczak, an infectious disease expert at Massachusetts General Hospital, and her team, some people have tested positive even though they did not have positive viral cultures, which indicate infectious virus. This suggests that tests are detecting lingering viral remnants rather than any infectious virus.

    What should you do if you keep testing positive?

    According to CDC's current Covid-19 isolation guidance, people can end their isolation after five days if they no longer have a fever and their other symptoms have improved. However, if symptoms continue, it recommended that people isolate until their symptoms subside and wear a mask through day 10.

    Currently, CDC does not require people to test negative before they end their isolation. For people who do choose to test themselves, the agency recommends people who test positive to isolate until day 10, while those who test negative can end their isolation but should wear a mask until day 10.

    However, there is no clear consensus about whether people should continue to isolate past 10 days if they are still testing positive.

    Michael Mina, an epidemiologist and chief science officer at eMed, said people who test positive should assume they are infectious, which will allow them to adjust their behavior and be more careful around others to avoid spreading the virus.

    Separately, Aubree Gordon, an infectious disease epidemiologist at the University of Michigan School of Public Health, agreed with Mina's assessment. "They're probably less contagious than they were in the first few days," she said. "But I would still certainly advise some caution."

    While some health experts recommend people isolate until they test negative, others argue that it doesn't make sense to ask people who are otherwise healthy to isolate or test past 10 days.

    "Nobody's saying that there aren't some people, maybe statistically speaking at the end of the tail, who might transmit after Day 10," said Peter Chin-Hong, an infectious disease specialist at the University of California, San Francisco. However, people at this stage are not likely to play a large role in viral transmission, and continued testing could keep many people out of school or work.

    "And also you raise an equity issue," Chin-Hong added, "like 'Who on Earth can have enough tests?'"

    In addition, Mina noted that there are other ways to reduce viral spread than just isolating, including choosing not to visit vulnerable family members or attend crowded public areas, including churches and bar, until you test negative. 

    "It's not just isolating, and never has been," Mina said. "It's all the little things you can do to prevent infecting someone else, even without isolating." (Anthes, New York Times, 5/31; NBC Chicago, 5/23)

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