COVID-19 Rapid Tests Can Breed Confusion – Here’s How To Make Sense of the Results and What To Do, According to 3 Testing Experts

Yves here. Some news you can use on the Covid front, although some of it is delivered more cautiously than is warranted. For instance, the article says it might be good idea to retest as after five days of a positive Covid test rather than assuming it is safe to go back to work or otherwise mingle with other people.

Also see these pointers on swabbing technique:

By Nathaniel Hafer, Assistant Professor of Molecular Medicine, UMass Chan Medical School; Apurv Soni Assistant Professor of Medicine, UMass Chan Medical School; and Yukari Manabe, Associate Director of Global Health Research and Innovation Professor of Medicine, Johns Hopkins University. Originally published at The Conversation

As fall temperatures set in, cold and flu season gets into full swing and holiday travel picks up, people will undoubtedly have questions about COVID-19 testing. Is this the year people can finally return to large gatherings for traditional celebrations? What role does testing play when deciding whether to go out or stay home?

Adding to the confusion are personal accounts of people who are experiencing confusing or seemingly contradictory test results.

We are part of a team that has developed and tested SARS-CoV-2 tests since the early days of the pandemic. Additionally, some of us are infectious disease specialists with decades of experience.

Our insights from both the cutting edge of rapid testing research as well as our clinical perspectives from working directly with patients can help people figure out how to make the best use of rapid tests.

Multiple Negative Tests, Then a Positive – Why?

SARS-CoV-2, the virus that causes COVID-19, takes time to build up in the body, like many other viruses and bacteria that cause respiratory illness. Typically it takes two to three days to test positive after exposure. Our research group has demonstrated this, as have others.

Rapid tests detect parts of the virus that are present in the sample collected from your nose or mouth. If the virus has not replicated to a high enough level in that part of your body, a test will be negative. Only when the amount of virus is high enough will a person’s test become positive. For most omicron variants in circulation today, this is one to three days, depending on the initial amount of virus you get exposed to.

A newscaster rapid tests for COVID-19 on live TV.

Why Do Some People Test Positive for Extended Periods of Time?

It’s important to clarify which type of test we’re talking about in this situation. Studies have shown that some people can test positive for a month or more with a PCR test. The reason for this is twofold: PCR tests are capable of detecting extremely small amounts of genetic material, and fragments of the virus can remain in the respiratory system for a long time before being cleared.

When it comes to rapid tests, there are reports that some people test positive for an extended period of time with the current strains of the omicron variant compared with earlier variants. Several studies show that most people no longer test positive after five to seven days from their first positive test, but between 10% to 20% of people continue to test positive for 10 to 14 days.

But why it takes longer for some people to clear the virus than others is still unknown. Possible explanations include a person’s vaccination status or the ability of one’s immune system to clear the virus.

In addition, a small number of people who have been treated with the oral antiviral drug Paxlovid have tested negative on rapid antigen tests, with no symptoms, only to “rebound” seven to 14 days after their initial positive test. In these cases, people sometimes experience recurring or even occasionally worse symptoms than they had before, along with positive rapid test results. People who experience this should isolate again, as it has been shown that people with rebound cases can transmit the virus to others.

Why do I Have COVID-19 Symptoms but Still Test Negative?

There are several possible explanations for why you might get negative rapid tests even when you have COVID-like symptoms. The most likely is that you have an infection of something other than SARS-CoV-2.

Many different viruses and bacteria can make us sick. Since mask mandates have been lifted in most settings, many viruses that didn’t circulate widely during the pandemic, like influenza and Respiratory Syncytial Virus, or RSV, are becoming common once again and making people sick.

Second, a mild COVID-19 infection in a person that’s been vaccinated and boosted may result in a viral level that’s high enough to cause symptoms but too low to result in a positive rapid test.

Finally, the use of poor technique when sampling your nose or mouth may result in too little virus to yield a positive test. Many tests with nasal swabbing require you to swab for at least 15 seconds in each nostril. A failure to swab according to package instructions could result in a negative test.

Our previous studies show that if you are symptomatic and do two rapid antigen tests 48 hours apart rather than just one, you are more highly likely to test positive if you are infected with SARS-CoV-2.

Self-swabbing: It sounds kind of cringy, but it’s really not so bad.

Do Rapid Tests Work Against the Current Strains of SARS-CoV-2?

Multiple studies have examined the performance of rapid testsagainst the omicron variant.

Fortunately, these studies show that all the rapid tests that have been authorized for emergency use by the U.S. Food and Drug Administration detect the current omicron variants just as well as previous variants such as alpha and delta. If a symptomatic person tests positive on a rapid test, they likely have COVID-19. If you are exposed to someone who has COVID-19, or have symptoms but receive a negative test, you should take another test in 48 hours. If you then test positive or if your symptoms get worse, contact your health care provider.

What’s the Best Way to Use and Interpret Rapid Tests Before Gatherings?

Testing remains an important tool to identify infected people and limit the spread of the virus. It’s still a good idea to take a rapid test before visiting people, especially older people and those with weakened immune systems.

If you believe you may be infected, the FDA recently updated their testing guidance largely based on data our lab collected. The testing regimen most likely to identify if you’re infected is to take two tests 48 hours apart if you have symptoms. If you don’t have symptoms, take three tests, one every 48 hours.

Does a Positive Test Mean You Can Spread COVID to Others?

The Centers for Disease Control and Prevention recommends that if you test positive for COVID-19, you should stay home for at least five days from the date of your positive test and isolate from others. People are likely to be most infectious during these first five days. After you end isolation and feel better, consider taking a rapid test again.

If you have two negative tests 48 hours apart, you are most likely no longer infectious. If your rapid tests are positive, you may still be infectious, even if you are past day 10 after your positive test. If possible, you should wear a mask. Multiple studies have showna correlation between the time an individual tests positive on a rapid test and when live virus can be collected from a person, which is a common way to determine if someone is infectious.

Testing is still an important tool to keep people safe from COVID-19 and to avoid spreading it to others. Knowing your status and deciding to test is a decision that individuals make based on their own tolerance for risk around contracting COVID-19.

People who are older or at higher risk of severe disease may want to test frequently after an exposure or if they have symptoms. Some people may also be worried about having COVID-19 and transmitting it to others who may be at higher risk for hospitalization. When combined with other measures such as vaccination and staying home when you’re sick, testing can reduce the impact of COVID-19 on all of our lives in the coming months.

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  1. Rip Van Winkle

    I’m leaning towards a dosimeter for radiation detection and checking my Potassium Iodide stash from 2011.

  2. Roger Blakely

    I have gone through fourteen fourteen-day cycles of COVID-19, and I have never tested positive. I am sure that after the first infection in March of 2020 my immune system kept the virus under control enough to avoid a positive test.

    I wear a respirator in all indoor public spaces. I still live in lock down. The goal is to minimize the fatigue, brain fog, and gastrointestinal misery.

    I have no doubt that this December will be as bad as the previous two Decembers.

    1. Mike Mc

      Caught COVID from a known anti-vaxxer at church – actually my wife did, this older gent is quite deaf and too cheap (despite quite well off) to buy hearing aids, so he leans in to talk – first week of August.

      NEVER had a positive home test, managed to convince local clinic to prescribe Paxlovid which kept me out of the ER due to lung problems. Had asthma as a kid so familiar with all the awful bronchial/lung noises, was hacking up copious amount of pink and green sputum. Paxlovid knocked this down quickly, though not so much the WORST sore throat I’ve ever had.

      Wife (62, I’m 67) didn’t have the same lung problems. She tested positive within 24 hours of exposure. We both isolated until she tested negative – again, I never tested positive.

      Scheduled our FIFTH shot for later this month (Team Moderna), already had our flu vaccines. I wear surgical masks in stores, have our N95s for colder weather (live in very SE Colorado, just starting to have lows of 40s here).

      Just some anecdata. We lasted 30 months before joining Club COVID. Trying to stay as healthy as possible to avoid long COVID. Sigh.

  3. CoryP

    Ugh swabbing my throat and then going halfway up my nose is unpleasant enough… I’m unhappy at the implication that I need to be doing a proper deep nasopharyngeal swab. :/

  4. Jeremy Grimm

    [Not sure my first attempt reached the moderatoration portal — if so please delete this 2nd attempt]
    This post did not dispel my Corona testing confusion. It sounds as if the rapid Corona tests
    work as well as the CDC guidance for controlling the spread of Corona infections. I do not
    understand this statement from the post: “… a mild COVID-19 infection in a person that’s
    been vaccinated and boosted may result in a viral level that’s high enough to cause symptoms
    but too low to result in a positive rapid test.” Just how sensitive are these rapid tests
    and why is it not possible to design a rapid test that can detect viral levels sufficient to
    cause symptoms? Given that a person can spread the Corona virus while non-symptomatic how
    valuable are these rapid Corona tests as a tool for slowing the spread of the virus? Are
    rapid Corona tests more effective than if a symptomatic person isolates when symptoms appear
    and remains in isolation for a period [>5 days?] after symptoms are gone? If someone is
    symptomatic, I really do not care whether they have the Corona flu, regular flu, or a cold
    of some kind — they should isolate to avoid spreading sickness. Knowing that you have
    contracted the Corona flu does not seem to be especially useful information given how little
    is known about attributing and treating its long term effects.

    It seems that the real problem is that whether a person has contracted the Corona flu or a cold the lack of paid sick leave tends to compel most people to continue going in to work whenever possible. The rapid Corona test seems at best like a way to compel the CDC directed minimum time a person must take off from work before an employer allows them to return — assuming they still have a job to return to.

    A couple weeks ago, Oct. 3, John McGregor linked to a Medical Xpress article
    referencing a recently published PNAS journal article describing evidence that the Corona
    virus infects brain tissues in some patients [“Morphological, cellular, and molecular basis
    of brain infection in COVID-19 patients”]. I was impressed by the technique used in the
    research described as follows by the Medical Xpress article:
    The researchers used a technique known as immunohistochemistry, a staining process in which
    antibodies act as markers of viral antigens or other components of the tissue analyzed. “For
    example, we can insert one antibody into the sample to turn the astrocytes red on binding to
    them, another to mark the SARS-CoV-2 spike protein by making it green, and a third to
    highlight the virus’s double-stranded RNA, which only appears during replication, by turning
    it magenta,” Martins-de-Souza explained. “When the images produced during the experiment
    were overlaid, all three colors appeared simultaneously only in astrocytes.”
    If a staining technique can resolve tissue level presence of Corona spikes, virus, RNA, why
    is it so difficult to develop a test that can detect the Corona virus at symptomatic levels
    or better at levels sufficient to identify a potential spreader of the virus, or better
    somehow identify potential super-spreaders with or without symptoms. Many of the Corona
    symptoms, especially for a mild case, do not seem greatly dissimilar from the symptoms of a
    sinus allergy.

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