Tanya Lewis: Hi, this is Your Health, Quickly, a Scientific American podcast series!
Josh Fischman: We bring you the latest vital health news: Discoveries that affect your body and your mind.
Lewis: And we break down the medical research to help you stay healthy. I’m Tanya Lewis.
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Fischman: I’m Josh Fischman.
Lewis: We’re Scientific American’s senior health editors.
Today we’re doing a followup episode on the best ways to use home COVID antigen tests. This time we’re looking at whether you get more accurate results if you swab your throat as well as your nose. We’ll also talk about possible new CDC guidelines about how long to isolate if you’re positive.
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Fischman: It’s February, and COVID levels are still quite high in the U.S. They’re way above what the CDC describes as epidemic levels, which means a lot of people are sick. Including me, as it turns out. Though I may just have a bad cold.
Lewis: Oh man, that’s rough. It seems like I’m constantly hearing about a friend or coworker testing positive for COVID. And that means a lot of people are taking home tests.
Fischman: Last month, you and I talked about a frustrating wrinkle in those test results.
Lewis: Yeah. People who got symptoms and tested right away were getting negative results–even though they were actually infected. And that seems to be because your immune system is now familiar enough with the virus to react quickly and cause symptoms like a runny nose or stuffy nose. But the virus itself hasn’t built up to high enough levels in your nose to trigger a positive test result. In other words, it’s a false negative.
Fischman: If you wait a few days after symptoms start–say, two to four days–and then you test, you’re more likely to get an accurate result. But that’s frustrating, right? You know you’re sick with something, and you don’t want to pass COVID around. But until you know for sure, you stay home, or you keep your kids home from school. And then maybe it turns out to be a winter cold, or the flu.
Lewis: It’s a good idea to stay home if you have any respiratory infection if you can, even if it’s not COVID. Even the flu kills thousands of vulnerable people every year. Still, it would be nice to know if you could reduce those early false negatives with COVID tests, and find out if you actually do have the virus.
Fischman: That’s why a lot of people are talking about swabbing your throat in addition to the nose. Two of our listeners, Ann and JD Stillwater of Pennsylvania, emailed us to ask how accurate throat swabbing is. There are a bunch of online videos touting that method now.
[5 SEC AUDIO SAMPLE from U.K. public health video starting at 2:14: “Stand in front of a mirror. Wipe the soft tip around the back of the throat as shown.”
Fischman: That was the U.K. Health Security Agency—the equivalent of our CDC.
Lewis: I’ve heard of that approach before - in fact I’ve swabbed my own throat on several occasions, when I wanted to make extra sure I wasn’t missing an infection. But it’s a surefire way to gag. Is it actually more accurate?
Fischman: It could be. Some scientists believe that, early in an infection, the virus replicates more in the throat than in the nose. So you’d be more likely to collect more virus. When it comes to studies of accuracy, they’ve mostly been on small numbers of people. And some of those studies say throats are more accurate. Others say they’re not more accurate.
Now, what seems to be one of the biggest, and one of the more carefully done studies on throat swabs was just published in December. So, we thought we’d go straight to one of the researchers.
Tobias Todsen: My name is Tobias Todsen and I'm a consultant … at Copenhagen University Hospital… I'm also an associate professor at the Copenhagen University… And I'm a consultant in otolaryngology.
Fischman: That’s an ear, nose and throat doctor to you and me. Todsen and his colleagues conducted a randomized trial, in Denmark, of about 2600 people. Some got nasal swabs, some got throat swabs, and some got both.
And some of them used the swabs on themselves, while others had a health care worker collect the samples. The scientists confirmed the presence of the virus with a molecular test, like a PCR test, and that’s the gold standard of accuracy here.
Todsen: We saw that there was a difference in when healthcare workers performed the test, and you did it yourself. So when the health care workers performed the test, then the throat was 9.4 percent better than the nasal swab….We didn't find any significant difference between the self collected swabs… comparing throat swabs with nasal swabs.
Lewis: So throat swabs were only more accurate when a health care worker did the swabbing. That makes sense. Speaking from personal experience, it’s pretty hard to swab your own throat.
Fischman: Yeah. And these are home tests, so going to a clinic to have a health care worker do one for you kind of defeats the purpose, doesn’t it? But Todsen found something else that was pretty important. And that’s got to do with combining nose and throat swabs in the same test.
Todsen: If home testing, if you combined… the nasal and the throat swabs, then you will… improve the sensitivity about 15 percent compared to nasal swabs alone. Meaning that combined swabs …nasal and throat swabs will… decrease the risk of false negative results.
Lewis: Wait. So he is saying that swabbing your throat only doesn’t detect more infections, but swabbing both your nose and throat does?
Fischman: Yeah, exactly. They used two separate swabs in the study, and then combined the samples. But since home test kits have single swabs, Todsen suggests using them this way:
Todsen: I would first make a throat swab on myself. And then I'll use the same stick for the nasal swab. And then I will handle this swab as you see in the instructions for the rapid antigen test you have bought.
Lewis: But those instructions, at least in all the U.S. home tests, say to swab the nose only. And besides, the FDA hasn’t approved any tests involving throat swabbing.
Fischman: Yeah. Look, Todsen thinks going both nose-and-throat will improve accuracy. Basically you’re hitting more places so that improves the chances of grabbing some virus. But it’s a bit tricky in the U.S. First of all, the swabs in our kits are pretty short. You want to get them to the top of your throat, kind of at the roof of your mouth and past your teeth. But it’s hard to reach that area unless you stick your fingers in your mouth, too.
Lewis: And that’s even more likely to make you gag.
Fischman: Sure is. I tried it myself, just last night, because I have sniffles and a sore throat. But like you, I made some icky sounds. If you look at that U.K. Health Security video, their swabs are a lot longer and easier to get in and out. And like you said, the U.S. tests aren’t calibrated for accuracy using both nose and throat. So we don’t really know how well they’ll perform. Todsen’s numbers say they’ll lower the rate of false negatives, and some smaller studies back him up. But clearly here the science is moving faster than the manufacturing. So I’ll back up my combined swab with a nose-only tomorrow. Meanwhile I’m staying home. Ann and JD from Pennsylvania, I know that’s not a cut-and-dried answer, but for now it’s what we’ve got.
Lewis: It does look like these ambiguous results from home tests might get a little easier to navigate in the near future. The distinction between what positive and negative strips mean for your behavior might not be so drastic.
Fischman: In what way?
Lewis: Well, the CDC has just changed the COVID isolation period. A positive test doesn’t automatically mean you need to stay home for five days anymore.
The agency has shifted to letting symptoms be your guide. If you’ve been free of fever for a full 24 hours, without the help of medication, and your symptoms are mild and improving, you don’t need to stay home.
Fischman: Wow. That is certainly a change!
Lewis: Yeah it is. Some people might say the guidelines are too lax—you could still be infectious after your fever goes away, so it’s not a perfect way to prevent all infections.
But the CDC might be trying to give people guidance they’re actually likely to follow—and treat COVID more like the flu or other respiratory infections now that we have some immunity and protection against it.
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Fischman: Your Health, Quickly is produced by Timmy Broderick, Tulika Bose, Jeff DelViscio, Kelso Harper, Carin Leong, and by us. It’s edited by Elah Feder and Alexa Lim. Our music is composed by Dominic Smith.
Lewis: Our show is a part of Scientific American’s podcast, Science, Quickly. Subscribe wherever you get your podcasts. If you like the show, give us a rating or review!
And if you have a topic you want us to cover, you can email us at Yourhealthquickly@sciam.com. That’s your health quickly at S-C-I-A-M dot com.
Just a quick request: my colleague Lauren Young and I are working on a podcast series on caregiving for older family members, and the challenges of navigating care at home vs. institutional care. We’re hoping to speak to people who have experience caring for their own family members. Please email yourhealthquickly@sciam.com with the subject “caregiving” if you’re interested.
For Your Health Quickly, I’m Tanya Lewis.
Fischman: AndI’m Josh Fischman.
Lewis: See you next time.
