PCR and rapid antigen tests, throat vs. nose swabs
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The midst of Covid’s omicron surgeIf you have symptoms, or were exposed to the virus, it is possible to be overwhelmed by the lack of tests available.
You might be wondering whether it is worthwhile waiting for hours to get a polymerase chains reaction (PCR test) or if your results can be trusted. an at-home rapid test — if you can even get one. Perhaps you have already been tested positive and need to be aware of how long you must wait until you stop being contagious.
There’s plenty of advice floating around for those types of dilemmas, especially on social media — and not all of it is worth taking. These are the top three suggestions from leading infectious disease specialists and microbiologists in America:
1. You can take 2 rapid tests if you don’t have a PCR.
The PCR is still the most reliable method of testing. However, if that’s not possible, you may be able to get two quick antigen tests within 48 hours. Matthew Binnicker Ph.D., Medical Director, Clinical Virology Laboratory, Mayo Clinic, Rochester, Minnesota.
He recommends you do a second test at home if you experience Covid symptoms such as fever, headache, sore throat or runny nose, and it is negative.
He says that PCR testing is recommended for influenza and Covid-19 if both of the tests come back negative. Binnicker suggests that you test for symptoms if you aren’t experiencing any, and do this on your third to fifth days after being exposed.
This is the Centers for Disease Control and Prevention’s definition of “healthy”. current guidanceAccording to, “Repeating the test in a few days with at least 24 hour intervals between each will improve your confidence that you’re not infected.”
It doesn’t hurt to have multiple tests, even if it feels fine. Repeated rapid testing for several days increases the likelihood of diagnosing infection. Christopher Brooke (PhD), an associate professor of microbiology from the University of Illinois Urbana.
studyBrooke and her coauthor, who published their findings in the Journal of Infectious Diseases last June, showed that both PCR (and antigen tests) can be used to detect 98% of Covid cases if done every other day.
2. Take a PCR to determine if you’re infected. Wondering if you’re still contagious? Do a quick test.
Rapid tests don’t have the same accuracy as PCR tests for Covid detection. They’re much more sensitive, too — making them the best tests to use to determine infection, says Dr. Scott Roberts, a Yale Medicine infectious diseases doctor and assistant professor at the Yale School of Medicine in New Haven, Connecticut.
However, they are not as useful for determining if you are still contagious. Roberts explains, “A PCR will still show positive if there is dead virus in your nose. It can take many weeks to recover from an infection.” It’s better to use rapid tests for contagiousness as they are more likely to detect a virus that is actively reproducing.
Binnicker warns that even if you are negative for a test, it is still advisable to be cautious. Small studyReleased this month were 30 cases of people using both rapid and PCR testing simultaneously. Four people passed the virus even though they had tested negative on the rapid test.
The CDC is still based on the same principle. recommendsEven if there are no symptoms, it is important to keep your face covered for at least ten days following your initial test for Covid.
3. Swab your nose, not your throat — at least for now.
Get advice swab your throat is making the rounds on social media, but experts are hesitant to recommend this — for now.
Only one small pre-print studyOn 382 individuals with COVID-19 symptoms, the accuracy of their saliva samples and those who were also tested for PCR was compared. This showed that the saliva tests detected all omicron cases and nasal swabs 86%.
However, there have not been any studies to directly test the nose and throat in rapid antigen testing. Binnicker also points out that at-home quick tests were only approved by the FDA for use as nasal swabs.
He explains that a throat swab could yield false positive results because these rapid antigen testing are affected by pH levels in the samples. Food and drinks can also influence the pH of the throat.
If you decide to do both, Brooke recommends swabbing your throat first, and then your nose — since the virus sometimes replicates in the throat first before moving into the nasal passages. The order of swabbing is [also]Because it’s grosser to sweep your nose in front of your throat,” he says.
Brooke states that it is an “off-label use” that is not in line with FDA guidelines.
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