You got your hands on a rapid antigen test to screen for COVID-19. The instructions are straightforward: Slide the swab up your nose and twirl it around for a few seconds. Pretty clear, right?
Maybe not. A new debate roiling the science community has cast doubt on the best way to detect a positive coronavirus infection using home testing kits. Some public health experts argue that swabbing your throat — in addition to your nose — will pick up the highly transmissible Omicron variant more quickly than swabbing your nose alone because the variant may replicate faster in your oropharynx, or the middle part of your throat, than in your nose.
The hashtag #SwabYourThroat has taken off on Twitter, where users are posting anecdotal reports of testing positive only after swabbing their throats when using antigen tests. Even the director of the Maine Center for Disease Control and Prevention, Dr. Nirav Shah, said there is “no clear or right answer” on the nasal versus throat swab debate, and if he were administering a rapid test, he’d “go with the back of the throat.”
Others, including the Food and Drug Administration, have cautioned against this off-label approach.
“It’s not that antigen tests are not detecting Omicron; they’re detecting it just fine. But people are getting quite infectious and getting infectious even before the virus has a chance to grow and get into the nose,” said former Harvard epidemiologist Dr. Michael Mina, chief science officer for eMed, a digital health and testing company, at a press briefing Thursday. The method of self-testing with a throat and nasal swab, he added, is also prevalent in the United Kingdom.
“I personally do swab my throat and my nose to get the best sensitivity when I use the over-the-counter tests at home,” he said.
The FDA has warned against throat swabs, a technique that has not been authorized by the agency for collecting at-home test samples, citing concerns about safety.
“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,” a spokesperson said in a statement to the Globe on Friday.
Safety risks include injuries to the tonsils or throat, the agency said. Throat swabbing may also induce vomiting and cause aspiration pneumonia, which occurs when food, saliva, or other liquids are inhaled into the lungs.
”Pieces of the swab may break off, as they may be more fragile and are not designed for throat swabbing,” the statement continued.
The debate comes on the heels of emerging research on the sensitivity and accuracy of rapid antigen tests. Citing an ongoing study from the National Institutes of Health, the FDA announced late last month that “antigen tests do detect the Omicron variant but may have reduced sensitivity,” compared with molecular PCR tests, which are considered the gold standard for diagnosing COVID-19. But unlike antigen tests, which produce results within 10 or 15 minutes, PCR tests are processed in a laboratory and can take several days to deliver results.
A small study, released earlier this week, also indicates that nasal-based antigen tests are slower to detect COVID-19 than saliva-based PCR tests in the early days of infection. The study, conducted by members of the COVID-19 Sports and Society Working Group, looked at 30 vaccinated people across five workplaces in San Francisco and New York.
On the day of their first positive PCR test and the day after, each person’s rapid antigen tests produced false-negative results, the study found, even though 28 of the 30 cases had high enough levels of the virus to infect other people. The study was a preprint and has not yet been peer-reviewed.
Tara Smith, an epidemiologist at Kent State University College of Public Health, said the research suggests saliva samples may catch Omicron infections more quickly than nasal swabs and that rapid tests might not produce positive results until after symptoms develop. But she was “very hesitant” to recommend swabbing your throat in addition to or instead of swabbing your nose when using a rapid antigen test without more evidence.
“The tests were approved only for nasal swabs and so deviation from that protocol could result in false positives or negatives,” Smith said in an e-mail to the Globe. “I wish the companies would release data on throat swabs — surely they have seen these anecdotes and could easily do the tests.”
Dr. Helen Boucher, an infectious diseases physician at Tufts Medical Center, agreed with this assessment.
“I am in the camp of following package insert and FDA-approved language and recommendations because that’s how these tests were studied and authorized,” Boucher said. “It’s really important in my mind that we at least follow the directions so that we can rely on the results that we get.”
Swabbing your throat, she added, “is not necessarily the easiest procedure — you could inadvertently harm yourself doing that.”