Nevada Halts Use of Rapid Coronavirus Tests
Nevada Halts Use of Rapid Coronavirus Tests in Nursing Homes, Citing Inaccuracies:
https://www.nytimes.com/2020/10/07/health/nevada-covid-testing-nursing-homes.html
Quidel and their Sofia antigen test is the "game changer" that was cited as one of the reasons the Big Ten and Pac-12 back to play this season.
October 8th, 2020 at 7:16 PM ^
One of these days, there’s going to be be blood.
There’s going to be blood everywhere.
And it isn’t gonna be from me, oh no no.
October 8th, 2020 at 7:18 PM ^
So... quick fixes and easy solutions don't always work, eh?
(To be fair, the problem is false positives - which is much more preferable than false negatives.)
October 8th, 2020 at 7:21 PM ^
That was something I was going to add. A false positive in a patient in a nursing home has different implications than a false positive for a college athlete. I also think the Big Ten players will be getting tested more often so a false positive could be weeded out with additional tests.
October 8th, 2020 at 7:50 PM ^
Do you happen to know what causes false positives? One possibility is contamination of the test. But I guess--and I don't actually know anything about this, so this is a real question--is that there is something about the person who falsely tests positive that means they'll continue to falsely test positive. (Maybe they have another coronavirus, for example, and the test can't distinguish coronaviruses well enough.) In that case, being tested more often wouldn't weed out false positives, at least not if they're using the same test.
Thoughts from better informed people?
October 8th, 2020 at 9:07 PM ^
Occasionally there is going to be a systemic error (one that repeats every time you run the test) which for a typical immunoassay, as you suggested, is most often going to relate to an unfortunate cross-reactivity of some sort with some protein other than the target.
But most often, the error is going to be a one-off that owes to the stochastic nature of protein binding. Lateral flow assays (see Covid Neck Sharpies Part II) depend on moving bits: the patient's sample is added to a buffer and then wicks along the test strip until it hits one of two lines of antibody complexes.
If it's a false positive, and not a systemic error, most of the time there is going to be an inappropriate binding (or even some antigen just getting stuck in the wrong place for some purely mechanical reason) that you wouldn't mathematically expect. Sometimes the visualization dye sticks to the wrong place. Things just stick or don't stick when they're not supposed to.
But that's all protein binding really is at the end of the day: affinity of antibodies for antigens that are just probabilities. It's never going to be completely clean when you're running a bunch of protein up a piece of paper.
Ghosts in the machine, man.
October 8th, 2020 at 9:53 PM ^
God bless you and you willingness to educate the internet.
I hope that one day we work together(even if I never know it) on a project to positively affect patient’s (people’s) lives.
October 13th, 2020 at 11:26 AM ^
Great answer, thanks!
October 8th, 2020 at 10:51 PM ^
False positives in an antigen test would be any molecule in the sample that is similar in structure to the target you’re testing for and cross-reacts. Example: methamphetamine and cold medicine (pseudophed). The bigger issue is false negatives due to dilution of the sample, thus dropping the protein to below detectable levels. Actually, if you want to pass a urine drug test, chug a gallon of water an hour before the test and you’ll be negative - note: most places test for dilution.
There’s really no way to counter this other than increase testing frequency and/or use a more sensitive test like the PCR.
October 8th, 2020 at 11:19 PM ^
But PCR tests have another flaw in that the +/- result of the test can change based on the number of cycles you run with it. Too few cycles and you risk a false negative, too many and you risk a false positive. There is, unfortunately no perfect test for this virus.
October 8th, 2020 at 8:07 PM ^
Didn’t they say regardless false positive you gotta quarantine?
October 8th, 2020 at 8:54 PM ^
The Big Ten has said if you test positive with the rapid test you then get a nasal swab to confirm. They will likely have to quarantine while waiting for the nasal test results but it won't be the full 21 days unless it is confirmed on the nasal one.
October 8th, 2020 at 7:55 PM ^
I was told the problem was the testing In and of itself
no tests. No pandemic
October 8th, 2020 at 8:03 PM ^
To be faaaahhr...
October 8th, 2020 at 8:23 PM ^
to be faaaaaaaaaaahhhrrr...
mcmurray’s a piece of shit.
October 9th, 2020 at 5:28 PM ^
can confirm
October 8th, 2020 at 8:43 PM ^
I think high false positive rate for rapid test was at least somewhat known. I seem to recall that the process in the B1G calls for anyone has a positive result from a daily rapid test to get a confirmation test with a nasal swab. So the rapid test is more or less a pre-screen to see who needs to get the real test.
I assume that means if you get a positive result from a rapid test but are cleared as negative with a nasal swab then you are cleared to play.
October 8th, 2020 at 7:19 PM ^
A higher than desired false positive rate doesn't seem like a reason to totally abandon it. You'd much rather have some false positives, which you can then retest with something more accurate. A high rate of false negatives would be MUCH more worrying.
October 8th, 2020 at 7:22 PM ^
Wasn't advocating for abandoning it, but I was highlighting that there is still a lot of unknown about the rapid tests. Combine that with the fact the Big Ten has given themselves no wiggle room with a season without bye weeks. Could a false positive test or tests lead to a game cancellation?
October 8th, 2020 at 8:22 PM ^
I am wondering why the B1G didn't schedule in a few bye weeks (willful ignorance?) Surely the season could already started? I recall Coach Harbaugh and others saying they could be ready to play in 2 weeks time!
October 8th, 2020 at 8:33 PM ^
They have to be equal to the whole conference. A few members had shut down practices (unlike M and OSU) and others = Wisconsin - had a compete campus in quarantine until late September.
Thus the only “fair” thing was to start the season 4 weeks from the end of the UW quarantine which left no wiggle room in the schedule.
October 8th, 2020 at 7:24 PM ^
I am not at all qualified to speak on this but as an unqualified opinion, this...
BD and Quidel’s advertised accuracies are impressive, but “they’re also the ones who made the test,” and are more likely to use it correctly, said Dr. Valerie Fitzhugh, a pathologist at Rutgers University. When confronted with the messiness of real-world conditions, rapid tests like these might not pass muster, she said.
...comes off as oblivious. We are in a pandemic--pick a level of false positives that is appropriate even if Rutgers people are handling them and LFG. The level we need to get to is whether the inconvenience of false positives is greater than the inconvenience of social distancing.
October 8th, 2020 at 7:51 PM ^
From the article:
"Among 39 positive antigen test results from both BD and Quidel, 23 were found by P.C.R. to be negative — an error rate of nearly 60 percent."
I mean, potentially small sample size and all. But that strikes me as absolutely terrible.
October 8th, 2020 at 9:04 PM ^
60% of the time it works every time
October 8th, 2020 at 9:14 PM ^
Out of how many tests overall?
October 9th, 2020 at 8:58 AM ^
Additional quote from the article:
"The results, which were collected from a dozen facilities where thousands of tests had been performed."
We really need to know more about those 39 teste to draw any conclusions. Were they the ONLY positive tests that had PCR follow-ups? If they weren't the only ones, how did they choose those to do follow-up PCRs? I also think that we tend to be missing the point of these rapid tests. Even if they aren't 100% accurate (or 95% accurate) getting results in 15 minutes is extremely beneficial. You identify people that are likely positive, have them isolate, and take the PCR test to confirm. It is like an improved version of the temperature check.
October 8th, 2020 at 7:53 PM ^
The other issue, and it's a big one, is the extent to which some people got it into their heads that the antigen test would necessarily catch infected individuals before they became contagious to others.
See, e.g.
Northwestern Dir of Spts Medicine Jeff Mjaanes says antigen testing is so good, it can “detect a level of virus thought to be below the level of infectivity.”
— Teddy Greenstein (@TeddyGreenstein) September 16, 2020
So positive cases can be identified and isolated before a player is contagious. HUGE.
To be fair, it wasn't just don't-call-him-Teddy-Ballgame, there was a lot of this sentiment going around.
But the support for this proposition in the literature has always been very thin at best and to the best of my knowledge falls more along the lines of "marketing puffery" than established fact at this point. That's a big deal, as the NFL and White House among others have found, because using a testing regime as the end-all is inevitably going to have a few sneak through the fence. And then it's off to the races once the virus is inside the gates.
October 9th, 2020 at 10:42 AM ^
Not gonna lie. You're my favorite pandemic era poster. I've reached a weird fanboy type of admiration for your posts. Mad technical and science skillz meets approachable layperson explanations topped off with magical witticisms.
A Sopwith Tiger Beat poster would adorn my bedroom wall if (a) I was 13 and (b) you had a Tiger Beat spread.
October 8th, 2020 at 7:55 PM ^
Step one: Nevada
Step two: ... Big Ten football ....
Step three: ...........
Step four: PROFIT!!!!!
October 8th, 2020 at 7:59 PM ^
Ehr boy.
October 8th, 2020 at 8:00 PM ^
I used to work for BD. I have nothing more to add than that.
October 8th, 2020 at 8:56 PM ^
I'm beginning to think all these tests aren't what they're cracked up to be.
October 9th, 2020 at 1:37 AM ^
Oh well, it looks like the season will be called off again.
October 9th, 2020 at 9:28 AM ^
These tests were chosen because they have a very high negative predictive value, meaning that if a test is negative, you can be sure it is negative. It has about a 97% specificity value meaning that you will get false positives. This is why they perform the PCR test for all who test positive with the rapid test. This is the type of test you want to screen people to make sure they are negative before allowing anyone to play.
October 9th, 2020 at 10:48 AM ^
My understanding of the way these tests work is that in order to minimize false negatives, which is obviously critical, they have to set them up in a way that results in a considerable number of false positives. This as explained to me by a biomedical type.
That person was working with another government on their response plan and their intent for this type of test was only to screen people as 'almost certainly uninfected", and anyone who tested positive would need the lab test to see if it was a false positive.
If this is the same type of test, it seems negligent for them to have been presented as having "no false positives".
October 9th, 2020 at 11:30 AM ^
I'm more concerned that people will be contagious and spread the virus before it would show up on rapid testing. That seems to be what happened at the White House (I started a thread about this that was immediately downvoted into oblivion and closed, so I guess I'm doubling down).
October 9th, 2020 at 12:27 PM ^
False positives are a huge issue in nursing homes right here in Michigan.
I get a weekly call from my grandmas nursing home updating me on positive cases there. Literally every time they say they had X amount of positives but then the second test shows they were false positives
October 10th, 2020 at 6:29 PM ^
In my son's hockey organization, two brothers on two different teams received false positives for COVID via the rapid tests. Due to shared ice practices, the ripple effect these positives had throughout the organization was incredibly disruptive to ~50 families lives. Teams temporarily shut down, kids held out of school and other extra curricular, tournaments/travel canceled, etc. On top of that, it just created confusion as different groups / schools have different protocols and people were scrambling to try to do the right thing.
I fully appreciate no one got sick and this ultimately ended up as simply an inconvenience, but it demonstrates how inaccurate tests only further disrupt what are already challenging times.