Post #872: COVID-19 spit tests for sale at Safeway

Posted on October 19, 2020


Places near Vienna VA offering COVID-19 nasal swab PCR tests.   Some but not all offer free testing.  You can search for free test sites on the Virginia Department of Health website.  Source:  Virginia Department of Health

I got my flu shot over the weekend, despite the fact that it’s not terribly effective (Post #741).  That took place outdoors, in front of the Pan Am Safeway. If felt a bit third-world, to be getting medical care outdoors.  But it was clearly the smart thing for them to do, in terms of coronavirus safety.

While I was there, at the pharmacy counter, I noticed a little sign stating that they had coronavirus spit tests for sale.  They were vague on details, and talked about insurance coverage of the test.  But they definitely had them. 

Of course, this being health care, it’s not like they listed a price or anything.  (And based on this article, I now know why:  $139! Which appears to be their standard price for it nationwide.  And, separately, something in that range appears to be more-or-less the going rate for at-home coronavirus test kits.)

Given that I wanted to be done with my flu shot as fast as possible, with as little interaction with others as possible, I wasn’t of a mind to chat up the pharmacist about it.  So I’m more than a little hazy on the details.  But, at least according to that sign, it sure looks like if you have the cash, they have the test.

I found it interesting for a few reasons.  Let me work through it, briefly.

What is a spit test?  Well, it tests your spit for the presence of coronavirus.  Some of those tests then look for the DNA of the coronavirus, same as the nasal swap PCR test does.  Others just look for certain surface proteins on the virus.

Any explanation beyond that falls into Arthur C. Clark’s dictum that any sufficiently advanced technology is indistinguishable from magic.

How do they work?  For some, you just spit in a test-tube.  Others are rinse-and-spit.  As far as I have been able to determine, all of those currently for home use  require that you mail your sample in to a lab for processing.   (And those labs will then inform local health officials if you test positive.)  Based on the news reporting cited above ($139), the Safeway test needs to be sent into a lab.  Some other home tests also require either physician authorization or physician supervision via telehealth.

Any instant-read tests (like pregnancy tests)? Not for home use.  Yet.  There are some fast-reading tests, but as far as I could tell, none for home use.  Here’s a press release from Abbott Pharmaceuticals, for a $5 test that provides results in 15 minutes.  But that’s a swab test, for use in a health care setting (e.g., clinic or physician’s office).   You can find several like that being offered currently.

How good are spit tests?  Well, that depends.  Here’s my summary of what I think I leaned from the scholarly literature.

First, you have to understand the current standard — the nasal swab PCR (DNA) test.  That’s what the accuracy of spit tests will be compared to.   The nasal swab PCR tests have a high false-negative rate (Post #859).  If one of those tests says that you have COVID-19 (positive test), then its virtually certain that you do.  But if it says that you don’t have it (negative test), that’s more of a suggestion than a certainty.  About 30% of people who truly have COVID-19 still manage to get a negative nasal swab test.

And so, if we’re talking about how accurate the spit tests are, that’s what they are being compared to.  How accurate are they, relative to a nasal swab PCR test.

I see a lot of conflicting claims about these spit tests, and that may relate to the variation among the tests.  At least some of them don’t “amplify” the viral DNA as much as swab-type tests, and so they are less sensitive at identifying cases with low viral load, compared to the swab tests. So they aren’t as good at identifying cases in the pre-symptomatic period, and at the tail-end of the illness, where viral load is low.

But for people who are really sick — say, hospitalized — from the handful of scholarly articles I’ve read, they appear to be as sensitive as the swab tests.  Possibly more so.

So, while these can and are being used for screening (testing people who aren’t ill), near as I can tell, their best use is for people who feel ill, and want to know if it’s COVID-19.  The beauty of that is that you don’t have to go somewhere and potentially expose some health care worker, to get yourself tested.

Rapid deployment.  What I find most fascinating about this is that, even a few months back, you could read articles stating that these spit tests wouldn’t be available any time soon.  But by mid-August, the FDA had already approved five different spit tests.  And here it is October, and you can buy one at the grocery store.

What we don’t have yet is a rapid-reading in-home spit test.  Something akin to a pregnancy test.  So far, all of the rapid-reading tests appear to be for health care professionals only, and most require a nasal swab.  (I.e., their sole advantage is rapid turnaround time compared to a nasal swab PCR test for COVID-19).

Summary:  If you want to get a COVID-19 test, have $139 to spare, and want to get your results in a few days, you can just walk into your local Safeway — well, really, any Safeway in America — and buy one.  I don’t think that’s terribly important from a public health standpoint.  You can get a free test in any of a dozen locations within a short drive of Vienna.  Nevertheless, I think that’s pretty cool that you can just walk into a store and buy a test.

Addendum:  As a final note, it’s not as if we lack for testing in Virginia.  Based on the technical notes on the Virginia Department of Health website, Virginia’s test figures count the number of unique people tested (and not the raw count of total tests, where some people receive more than one test).

Assuming that’s true, as of today, 2.4 million people in Virginia have been tested for coronavirus, or just under 30% of the entire state population.  For Fairfax County, 283,000 have been tested, or a little under 25% of the population.  For ZIP code 22180 (Vienna and environs), the total is 5883, or again, just under 25% of the population.