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If you never tested positive for COVID after exposure and symptoms, what does that mean?
Amid the latest COVID surge, those who never tested positive for COVID — even if they had symptoms or were repeatedly exposed to the virus — may be wondering what it means.
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Why do some people never test positive for COVID, even after exposure and symptoms?
Amid the latest coronavirus surge, those who never tested positive for COVID — even if they had symptoms or were repeatedly exposed to the virus — may be wondering what it means
Updated: June 13, 2022 12:28 p.m.
Amid the latest surge, those who never tested positive for COVID may be wondering what it means. COVID home antigen tests were hard to find during the winter omicron surge, but are now used widely.
Emily Jan / The Chronicle/The Chronicle
As the latest COVID surge continues to keep cases high across California, some people — especially if they’ve been repeatedly exposed to the coronavirus or even had symptoms — may be wondering: Why have I still not tested positive?
While experts continue to try to understand what, if any, genetic factors protect people from ever getting COVID, the question of why some people never seem to test positive, even if they are fairly sure they were infected, is a bit less of a mystery, though still not entirely clear.
Both laboratory PCR and home antigen tests remain useful tools in the pandemic response, said several experts during a recent UCSF grand rounds panel. But the home tests in particular have been somewhat unreliable at detecting infections, and the experts explored some theories on why false negatives may be occurring. Antigen tests, which detect proteins from the coronavirus, are generally less sensitive than PCR tests, which look for viral genetic material.
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For some people, a false negative home test may come down to user error, said Dr. George Rutherford, an infectious disease expert at UCSF.
“People can be squeamish about putting something in their nose and not get the right sample,” said Rutherford. “If you don’t do it vigorously enough, I can easily see how you’d end up with a false negative.”
But even for those who are administering the test correctly, vaccinated people may still get a negative result, even when they have symptoms and have been exposed, the experts noted. That’s partly because vaccination blunts the viral load, so they may not have enough virus in their nose or upper respiratory tract to register on a home test, or even, in some cases, a more-sensitive PCR test.
Some vaccinated people may eventually have a high enough viral load to be detectable on a home test, but they could have symptoms before they reach that point — so they might test negative for a few days even while experiencing a sore throat or other signs of illness. Some may never have a high enough viral load to test positive.
“People are being symptomatic earlier, before the viral load goes up,” said Dr. Peter Chin-Hong, a UCSF infectious disease expert.
Dr. Monica Gandhi, also an infectious disease expert at UCSF, added that studies have shown that if people are vaccinated, the viral load decreases quickly, which also shortens the time period in which they might test positive.
For some people, never testing positive may be a result of not testing frequently enough or at the right time, or simply having such a short infection that they never knew they had it,said Dr. Julie Parsonnet, an infectious disease expert at Stanford, said in an interview.
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What all this means for determining when and whether people are infectious isn’t clear, experts said. While a negative home test probably means that someone isn’t infectious, they said, it is not a perfect measure.
“We could all have a positive test two hours later,” after testing negative, Gandhi said.
But Gandhi noted that people who are vaccinated are “definitely” less infectious than those who are not vaccinated, which increases the likelihood that if they’re testing negative, they are probably not infectious.
“It does give us a (screening tool), like yes/no,” Chin-Hong said, “but there’s a gradation. … It’s not, again, a zero-sum game.”
Danielle Echeverria is a San Francisco Chronicle staff writer. Email: [email protected] Twitter: @DanielleEchev
Covid at Home: Why Only Some People Test Positive
The key to this household mystery may lie in our vaccination status, experts say.
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Your Negative COVID Test Is Basically Meaningless
A string of negatives can still presage a clear-as-day positive.
A Negative COVID Test Has Never Been So Meaningless
A string of negatives can still presage a clear-as-day positive.
By Katherine J. Wu
Getty; The Atlantic JUNE 10, 2022
In early May, 27-year-old Hayley Furmaniuk felt tired and a bit congested, but after rapid-testing negative for the coronavirus two days in a row, she dined indoors with friends. The next morning, her symptoms worsened. Knowing her parents were driving in for Mother’s Day, she tested again—and saw a very bright positive. Which meant three not-so-great things: She needed to cancel with her parents; she had likely exposed her friends; a test had apparently taken three days to register what her vaccinated body had already figured out.
Tests are not and never have been perfect, but since around the rise of Omicron, the problem of delayed positivity has gained some prominence. In recent months, many people have logged strings of negatives—three, four, even five or more days in a row—early in their COVID-symptom course. “I think it’s become more common,” says Amesh Adalja, an infectious-disease physician at the Johns Hopkins Center for Health Security.
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Read: COVID tests weren’t designed for this
No one can yet say how common these early negatives are, or who’s most at risk. But if SARS-CoV-2 is rewriting the early-infection playbook, “that makes it really scary,” says Susan Butler-Wu, a clinical microbiologist at USC’s Keck School of Medicine. “You can’t test and get a negative and actually know you’re negative.” Misleading negatives could hasten the spread of the virus; they could delay treatments premised on a positive test result. They also buck the current COVID dogma: Test as soon as you feel sick. The few days around the start of symptoms are supposed to be when the virus inside you is most detectable and transmissible; we built an entire edifice of testing and isolation on that foundation.
Experts aren’t sure why delayed positives are happening; it’s likely that population immunity, viral mutations, and human behavior all have some role. Regardless, the virus is “acting differently from a symptom perspective for sure,” says Emily Martin, an infectious-disease epidemiologist at the University of Michigan. That’s worth paying attention to. The start of symptoms has always been a bit of a two-step: Is it COVID, or not? If SARS-CoV-2 is re-choreographing its moves, we must too—or risk losing our footing.
Right now, experts are operating in a vacuum of evidence: “I don’t even know of any data that systematically evaluates this,” says Yonatan Grad, who’s studying the viral dynamics of SARS-CoV-2 at Harvard’s School of Public Health. But several phenomena could plausibly be muddying the testing timeline.
First, the immunity hypothesis, the most popular idea floated by the experts I spoke with. Perhaps symptoms are preceding test positivity, less because the virus is peaking late, and more because illness is arriving early, thanks to the lightning-fast reflexes of people’s primed immune systems. Sometimes, sickness is direct damage from a virus. But a runny nose, muscle and joint aches, chills, fevers, fatigue—which are common across many respiratory infections—can also be “signs that the immune system is being activated,” says Aubree Gordon, an infectious-disease epidemiologist at the University of Michigan. When the pandemic began, infections happened exclusively in people who’d never encountered the coronavirus before; illness took several days to manifest, as the virus churned itself into a frenzy and the immune system struggled to catch up. “Once people are vaccinated, though, their immune systems kick in right away,” says Emily Landon, an infectious-disease physician at the University of Chicago. (Prior infection, too, could have an impact.) If the body makes fast work of the invader, some people may never end up testing positive, especially on antigen tests. (PCRs are generally more sensitive.) Others may see positives a few days after symptoms start, as the virus briefly gains a foothold.
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But some of the experts I spoke with were a little hesitant to give the immune system all the credit. Some unimmunized people have experienced early negativity, too, and many people who have gotten their shots still test positive before falling ill.
SARS-CoV-2 traits, too, could be flipping the sickness script, which brings us to the virus hypothesis. Any member of the Omicron cohort is “just a different beast,” says Ryan McNamara, a virologist at Massachusetts General Hospital. It struggles to penetrate deep into the lower airway, and may not accumulate to the densities that Delta did in the nose, which could make false negatives more likely. A couple of studies have also found that Omicron may, in some people, be detected in the mouth or throat before the nostrils.