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January 10, 2022

Throat vs. nose? The debate over where to swab for omicron with rapid tests.

Daily Briefing

    Early data suggests that omicron proliferates more quickly in the throat than in the nose, leading some prominent experts to suggest that throat-swabbing may improve the accuracy of rapid Covid-19 tests. However, FDA and test manufacturers are discouraging the practice.

    Rapid tests may be less reliable with omicron, early data suggests

    According to STAT News, early data suggests that rapid Covid-19 tests are less reliable at detecting omicron than prior coronavirus variants, especially during the early days of an infection.

    For example, a small, preprint study of 30 people found that rapid Covid-19 tests often remained negative for several days after an infection was detected by PCR tests. In addition, the researchers documented four cases in which an infected person actually transmitted the coronavirus while their rapid test were still reporting negative results.

    Similarly, FDA in December cautioned that while rapid Covid-19 tests "do detect the omicron variant, [they] may have reduced sensitivity" and may be less likely to pick up early infections from omicron compared with molecular PCR tests.

    Why a throat swab might detect omicron earlier

    One reason why rapid tests may be faltering against omicron, some experts have suggested, is that the variant tends to replicate more rapidly in the throat—while the instructions on most rapid tests require samples to be taken from the nose.

    "It may be that omicron is showing us a slightly different set of symptoms, and that may reflect perhaps a change in where this virus is infecting in your respiratory tract or how well it's infecting certain cells in your respiratory tract," said Andy Pekosz, a virologist at the Johns Hopkins Bloomberg School of Public Health.

    Similarly, Eric Feigl-Ding, an epidemiologist and senior fellow at the Federation of American Scientists, said that omicron may result in "a greater concentration in your windpipe than ever before. It just replicates differently, and it clearly has a different potential tissue replication."

    To detect omicron sooner, then, some prominent experts have suggested swabbing the throat in addition to the nose.

    Michael Mina, the chief science officer at eMed, said on Twitter, "[T]here is a chance the virus isn't yet growing in the nose when you first test." Mina added, "Virus may start further down. Throat swab + nasal may improve chances a swab picks up virus."

    Similarly, Feigl-Ding said, "The fact that [omicron] replicates differently in different tissues means that you might have to sample different tissues."

    And according to a recent preprint study from South Africa, tests using saliva taken from throat swabs were better at picking up omicron than those using nasal swabs. The tests using throat swabs were able to detect 100% of omicron cases while nasal swabs only detected 86% of omicron cases, Insider reports.

    FDA cautions against throat swabs with at-home rapid tests

    So far, FDA has cautioned against using throat swabs with at home rapid tests, primarily since the tests were initially validated using nasal swabs.

    "The FDA advises that Covid-19 tests should be used as authorized, including following their instructions for use regarding obtaining the sample for testing," said Jim McKinney, an FDA spokesperson. "The FDA has noted safety concerns regarding self-collection of throat swabs, as they are more complicated than nasal swabs—and if used incorrectly, can cause harm to the patient."

    Some medical experts have expressed similar sentiments, TODAY reports, citing the need for data to ensure the accuracy of rapid tests using throat swabs.

    According to Roy Gulick, chief of the division of infectious diseases at NewYork-Presbysterian/Weill Cornell Medicine, the microenvironment of the nose is different from that of the throat, so not all rapid tests will produce valid results from samples in both places.

    "I can't recommend that people use these swabs in their throat. It's just not the way the tests have been authorized," Gulick said. "Please don't take matters into your own hands. We need to wait to see if any of these tests will be valid to do a throat swab as well."

    Currently, manufacturers of the most popular rapid tests in the United States, including Abbott Laboratories and Quidel, have said their rapid tests using nasal swabs are still effective at detecting the omicron variant.

    "In all cases, our studies confirm that BinaxNOW [rapid test] continues to detect the omicron variant at comparable viral load levels as all other variants and the original SARS-CoV-2 strain," Abbott said. (Herper, STAT News, 1/6; Pawlowski, TODAY, 1/5; Putka, MedPage Today, 1/6; Bendix/Brueck, Insider, 1/6)

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