Should you also swab your throat when taking a rapid test for Omicron?
Much more than you wanted to know
This idea was mentioned in a Washington Post article yesterday, despite clearly overstepping the protocols authorized in the FDA's current rapid test EUA’s. In this post, I'll lay out what I found when looking into whether it's a good idea. My focus will be on what you can do right now as an individual to get test results with maximum accuracy, rather than any wider policy change recommendations.
Disclaimer: I'm not a doctor, and this is not medical advice.
TLDR: More evidence is needed, but it sounds like there's a reasonable case to be made for this, and I plan to start doing it. Regardless, ordering an EUA-authorized saliva PCR home collection kit might be wise.
Starting in late December, some experts started recommending swabbing the throat for rapid tests
Based in part on the research in the next section, they proposed that individuals should jury-rig off-the-shelf nasal rapid tests into combined nasal and throat/saliva rapid tests. Here's the Washington Post article I mentioned at the top, written by Allyson Chiu: Should you add a throat swab to your at-home covid test? Experts disagree.
Shannon Palus at Slate also wrote an article about this the week prior.
And a brief mention in the New York Times.
The Washington Post article cites two prominent epidemiologists (Dr. Michael Mina and Dr. Eric Feigl-Ding) as proponents of throat swabs. Looking through their tweets, I found specific endorsements of throat swabbing from Dr. Feigl-Ding here and here, and from Dr. Mina here and here.
Notably, even the director of the Maine C.D.C appears to informally agree.
CBS13 took the issue of this different method directly to Maine CDC Director Dr. Nirav Shah. He says Maine CDC officials have asked the U.S. CDC about this.
“Individuals have to make the decision that's right for them,” Shah said. “There is no clear or right answer here. I'll tell you, if it were me, I'd go with the back of the throat."
Here are tweets I found from other physicians/scientists also endorsing this:
Dr. Kavita Patel - M.D., researcher/contributor at NBC and MSNBC
Dr. Jennifer Glass - Associate professor in the Georgia Tech School of Earth and Atmospheric Sciences with a courtesy appointment in Biological Sciences
Dr. Stephanie N. Langel - Scientist & Medical Instructor in the Duke Center for Human Systems Immunology
Dr. Swapneil Parikh - M.D., author
And here are some anecdata that I spotted on Twitter, for what they are worth. More can be found under the #SwabYourThroat hashtag:
Anecdata from 13 of Dr. Patel’s patients
Positive nose+throat rapid, negative PCR, negative nasal rapid
Positive nose+throat, negative nasal, later confirmed positive with PCR
Positive nose+throat rapid test, negative nose only rapid test
Positive nose+throat rapid test, negative nose only rapid test
Positive nose+throat rapid test, negative nose only rapid test
Positive nose+throat rapid test, negative nose only rapid test
Government endorsement of nose+throat swabs for PCR in the UK and Canada
Proponents of throat swabs highlight that Canada and the UK have both endorsed throat swabs already. The UK and Canada instructional videos for collecting a nose+throat swab are frequently cited.
From what I can see though, both countries have thus far issued throat swab guidance only for PCR testing, and not for use with rapid tests. If anyone reads anything to the contrary, please let me know and I'll update this. (credit to Atersed for correcting me on this)
Those two videos are both for PCR tests, but the UK health authorities also recommend a nose and throat swab in their instructions for some rapid tests, as you can see in this less-cited video.
On the other hand, another commenter says:
Recent UK self-test kits have been nose only.
The several "managed" LFD testing options I have been through in both the UK, Denmark and Greece have been nose only.
In fact, the only throat-LFDs I've seen are the first iteration of the UK self-test kits.
(-mseebach)
Why focus on the throat? Recent studies indicate Omicron infectiousness can be detected several days sooner by saliva than by traditional nasal testing
I started down this rabbit-hole after reading Zvi Mowshowitz's Omicron Post #13 today. It referenced this new study from the COVID-19 Sports and Society Working Group. Their study suggests that saliva PCR tests detect Omicron at infectious levels several days earlier than nasal rapid antigen tests. It sounds like they also saw evidence that nasal PCR's may be no better than nasal rapid tests for detecting Omicron infectiousness, though that particular finding was based on a subgroup sample size of only 5 people.
Here's an excerpt:
On Days 0 and 1, all rapid antigen tests produced false-negative results, despite 28 of 30 pairs having infectious viral load within the range of confirmed Omicron transmissions in the cohort (Ct < 29). The median time from first positive PCR to first detectable antigen positive was 3 days (95% Confidence Interval: 2-NA). After infection was detected, a subgroup (n=5) who received daily saliva PCR, nasal swab PCR, and nasal swab rapid antigen testing showed viral load peaked in saliva 1-2 days before nasal tests (Supplemental Table 1). All individuals in the cohort developed symptoms within two days of the first PCR positive test.
The authors reference prior research indicating that Omicron is specifically harder to find in the nose and easier to find in saliva vs. Delta:
Omicron has been shown to infect faster and more efficiently than Delta in human bronchus, but with less severe infection in lung, translating to symptom increase of sore throats and decrease of loss of taste and smell, better detected by saliva than nasal swabs.
It looks like their findings echo another, earlier study from South Africa which also found that saliva PCR samples are superior to nasal PCR samples for detecting Omicron.
Possible risks of this approach
I will list all risks that I have read and can think of here.
This week the FDA formally spoke out against swabbing your throat for a rapid test.
CNN reported on this here. An excerpted quote from an FDA spokesperson:
"The FDA advises that COVID-19 tests should be used as authorized, including following their instructions for use regarding obtaining the sample for testing," an FDA spokesperson told CNN this week. "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. The CDC recommends that throat swabs be collected by a trained healthcare provider."
The safety concern sounds like it might be a bit exaggerated given that the UK allows individuals to self-administer throat swabs, unless the physical swabs provided in those nose+throat kits are structurally different from nose-only swabs?
It’s much harder to dismiss the other concern raised in this article - physicians interviewed by CNN point out that - without a formal study - for all we know throat swabs may decrease test accuracy rather than improving it. Right now all we have are anecdata, and there have been plenty of COVID treatments and protocols that started out looking promising based on anecdata, but didn’t stand up to formal study (Hydroxychloroquin, Ivermectin, etc.).
The physicians interviewed in the Washington Post article who are opposed to throat swabs largely share the same concerns, and particularly raise the issue of potential false-positives (Dr. Mina agrees on that point).
It also occurs to me that - if it’s true that this new guidance applies specifically because Omicron is different - the reverse may also be true, and the guidance may degrade test performance for Delta. If Delta manifests more in the nose than in saliva, perhaps a throat+nose swab could be more sensitive than a nasal swab for Omicron, but less sensitive to Delta.
It's worth noting that even if throat+nasal swabs are actually more prone to false negatives than nasal-only swabs, we would probably see an under-representation of anecdata demonstrating that, because it sounds like a lot of people are only trying nasal+throat after getting an unexpected negative result from a nasal-only swab. Many tweets are along the lines of "I have symptoms but a negative nasal test, so I tried nasal+throat and got a positive." Fewer people are probably starting with a nasal+throat test, getting an unexpected negative, and then trying nasal-only.
If you’re worried about transferring the virus into the nostrils during this test protocol, Dr. Mina says don’t worry about it, and you may also be reassured by the use of this protocol in the UK and Canada.
The US actually does have some EUA-authorized saliva PCR tests, and you might want to buy one
It also turns out there are some saliva PCR tests that have received EUA's in the US. For example, this home collection kit available for $85 on Amazon. There's also this one (SalivaDirect) for $99.
Interestingly, the protocol for both of these appears to involve spitting into a tube, rather than the back-of-throat swabs used in the UK and Canada.
Given the convincing research that saliva tests are less prone to Omicron false-negatives than nasal PCR's, I'm going to buy one to have at hand in case I want to confirm infection when I feel symptoms or get a positive rapid test.
If you want to do a throat swab with a rapid test, how should you do it?
The physicians/experts who endorse this method often point to the PCR collection instructional video from the UK's public health authority, and recommend no eating or drinking for 30 minutes prior. For example, here's Michael Mina's tweet again.
Canada has essentially the same instructional video, though geared towards collection by a professional.
I’ll mention that one of the US-authorized saliva PCR tests (SalivaDirect) also tells you not to vape or smoke for 30 minutes before your test. It might be wise to add that to your procedure as well.
Both Canada and the UK tell you to avoid swabbing the teeth or tongue. It's worth noting that the pro-saliva study from South Africa used a different method for collecting saliva by swab for their PCR's. Excerpt:
Swabs were self-collected by the study participants under supervision of a healthcare worker.
Participants should not have had any food, drink, tobacco or gum in the 30 minutes preceding saliva swab collection. Participants were initially instructed to cough 3-5 times, covering their mouths with the inner elbow. They were then asked to swab on the inside of both cheeks, above and below the tongue, on the gums and hard palate. A minimum swabbing duration of 30 seconds was required. The swab was transported in a sealed container to the laboratory without any transport media.
The study Zvi mentioned from the COVID-19 Sports and Society Working Group doesn't list what technique they used for saliva collection. It's possible that they may not even have used a swab - some saliva PCR tests have you spit into a tube instead.
That's all the information I've found so far on this. My personal takeaways:
When I want maximum certainty that I don't have COVID, if I have a good number of rapid tests on hand, I'm going to start taking two rapid tests simultaneously. One nasal rapid test using the traditional EUA-authorized protocol, and one throat-and-nasal rapid test. For the latter, I'll be following the instructions in the video produced by the UK government here, and avoiding eating, drinking, smoking or vaping (not that I’m that hip anyway) for 30 minutes beforehand. I’ll try to space out the two tests by an hour or so, to make sure there’s material in my nose for both tests to collect.
If I start to run low on tests, or if I think my exposure risk has been low, I'll perform only one test and do both a nose and throat swab. I’ll reevaluate that in a week or so based on the latest evidence/anecdata.
I'm also ordering an at-home saliva PCR collection kit to keep on hand for confirming any positive rapid test.