Pool testing problems

Posted

Specializes in School Nursing. Has 7 years experience.

I've been helping a school doing pooled testing (through Concentric). The protocol is to do pooled tests that are couriered to a lab for PCR, and then we follow up on any positive pools with individual antigen tests (BinaxNow) in the hopes of immediately figuring out who triggered the result.

We've had positive pools by PCR multiple times, only to have every single antigen test in that pool come back negative. In one case, one of the students became symptomatic two days later, so I assume she was brewing an infection and just didn't have enough virus in her nares to trigger a positive result. But on all the other ones - nada.

We've double checked the expiration etc on the Binax Now, tried using a different box of tests to immediately re-test students, triple-checked the protocol, had the nurses collect the samples rather than the students, meticulously rechecked every step of the process in place...but, nothing.  Positive PCR, negative antigen.

I would expect this to happen sometimes just due to the difference in sensitivity between the two tests, as in the situation I described above, but I wouldn't expect it to happen almost every week. I wouldn't expect those all to be false positive PCRs. And the pools coming back positive do NOT include any kids with a COVID diagnosis within the last three months, so I don't think we're catching coronavirus RNA scraps from a previous infection.

It's really frustrating, and the school is questioning whether it's even worth the time/money to test. There's not a way for the BinaxNow swabs to reflex to PCR testing  - they'd have to send all the kids home to PCR test in clinics or pharmacies. This makes sense conceptually and clinically, but is also likely to seriously erode parent support for the in-school testing.

Is this a common problem? Does someone else use a better protocol?  How about you @JenTheSchoolRN?

Edited by laflaca

k1p1ssk, BSN, RN

Specializes in pediatrics, school nursing. Has 10 years experience.

Is the pooled testing a saliva sample or is it also a nasal swab? At the private school I work at, we did weekly saliva PCRs on all students & staff last year (through Ginkgo by Concentric). We had a lot of this scenario - a positive would turn up on the saliva test, we would go to confirm with a AN Swab PCR & Rapid Antigen - often a BinaxNow, and frequently they would be negative on multiple subsequent PCRs and Binaxes. All students were asymptomatic, and hadn't left campus. The one thing they all admitted to have done was eaten and/or drank in the 30min prior to doing their saliva test. Even just drinking water...

This obviously means nothing if you're doing nasal swabs, but something to consider if your pools are the saliva tests...

laflaca, BSN, RN

Specializes in School Nursing. Has 7 years experience.

@k1p1ssk Interesting! Ours are all nasal swabs though (Concentric by Gingko also).

Edited by laflaca

Jedrnurse, BSN, RN

Specializes in school nurse. Has 29 years experience.

The protocol in my state is if you don't identify a positive with the Binax reflex testing the first day then it should be repeated the next. (There is also the option at that point for sending individuals out for PCRs.) In your situations, did you do the second day of testing?

(I had one positive pool so far this year. The Binax reflex testing picked up the positive the next day and he became symptomatic a couple of days after that...)

laflaca, BSN, RN

Specializes in School Nursing. Has 7 years experience.

@Jedrnurse  No, the setup for staffing (the schools get funding for outside help) is two consecutive days. So on day 1, collect the pooled specimens; get the results overnight; day 2 is for antigen followup on positive pools.

I don't think they have the ability to staff for a third day - the school nurse would have to do it, and they're already so overwhelmed.

Edited by laflaca

MHDNURSE

Specializes in Pediatrics, Community Health, School Health. Has 25 years experience.

We have definitely been in this situation a few times.  The main issue is that Binax is definitely MUCH better at detecting the virus in symptomatic subjects- this is the main reason why I have a huge problem with Test to Stay- we have had several kids in this program be identified as CC to test negative's e a few days and then suddenly turn positive on day 3-5 as soon as their symptoms start.  And then we are having to now test a bunch of new CC's in the school because these kids were in class and they were +.  Currently, if a + pool is resulting in all - Binax, those kids are then PCR'd to confirm.  But any in the TTS are presumed - on only a Binax.

JenTheSchoolRN, BSN, RN

Specializes in School nursing.

So I've been using BinaxNOW - today I had another positive pool pop overnight and my positive student in it popped right on BinaxNOW immediately. And kid was asymptomatic. 

BinaxNOW is very good for folks with symptoms, but I have been surprised at how easily it helped me identify asymptomatic students. 

But if I hit an all negative BinaxNOW, I would do an individual PCR follow-up. My school gave a budget to do that thankfully if my state didn't cover it AND the state protocol in MA just changed to allow this. 

If your protocol is sound - I also collect the samples myself vs letting students to do and actually do a pretty firm five times around in the nose - I'm trying to think what else is going on for it to happen every time...

laflaca, BSN, RN

Specializes in School Nursing. Has 7 years experience.

7 hours ago, JenTheSchoolRN said:

So I've been using BinaxNOW - today I had another positive pool pop overnight and my positive student in it popped right on BinaxNOW immediately. And kid was asymptomatic. 

BinaxNOW is very good for folks with symptoms, but I have been surprised at how easily it helped me identify asymptomatic students. 

But if I hit an all negative BinaxNOW, I would do an individual PCR follow-up. My school gave a budget to do that thankfully if my state didn't cover it AND the state protocol in MA just changed to allow this. 

If your protocol is sound - I also collect the samples myself vs letting students to do and actually do a pretty firm five times around in the nose - I'm trying to think what else is going on for it to happen every time...

I know, it's crazy. I was convinced it had to be a bad box of the BinaxNow tests...but, nope, we switched boxes with the same results.  Not expired, haven't been out in the heat or anything.

And the ones coming back *positive* (the pooled tests) are mostly done by students - the follow up ones coming back *negative* are all done by RNs - all of us are doing firm vigorous twirls.

Having a budget/supplies for PCR testing would be logical, but I suspect it's not possible here. I guess the options are for the school nurse to re-test for the next day or two, or to call parents and send them out for PCR.

JenTheSchoolRN, BSN, RN

Specializes in School nursing.

On 10/21/2021 at 8:26 PM, laflaca said:

I know, it's crazy. I was convinced it had to be a bad box of the BinaxNow tests...but, nope, we switched boxes with the same results.  Not expired, haven't been out in the heat or anything.

And the ones coming back *positive* (the pooled tests) are mostly done by students - the follow up ones coming back *negative* are all done by RNs - all of us are doing firm vigorous twirls.

Having a budget/supplies for PCR testing would be logical, but I suspect it's not possible here. I guess the options are for the school nurse to re-test for the next day or two, or to call parents and send them out for PCR.

You have been getting enough liquid on the BinaxNOW test, I'm guessing? They say 6 drops, but honestly I've found 8 drops to be more accurate. They never send enough solution for me in the box of 40 tests I get!

I have all my kids self swab now for the pools - transitioned to this earlier this year after I could make sure all the kids did it properly. 

Jedrnurse, BSN, RN

Specializes in school nurse. Has 29 years experience.

1 hour ago, JenTheSchoolRN said:

You have been getting enough liquid on the BinaxNOW test, I'm guessing? They say 6 drops, but honestly I've found 8 drops to be more accurate. They never send enough solution for me in the box of 40 tests

This is definitely a pain and a pain I have experienced. Have you heard of anyway of getting just an extra reagent bottle? My project coordinator said the only way is to order full kits...

Cattz, ADN

Specializes in School Nurse. Having conversations with littles.. Has 35 years experience.

Could it be that it is measured out for 6 drops per test and this may have something to do with the bottle of reagent not being enough to last for the whole box? Thank you, you have taught me something. I have been afraid that I would accidentally let a drop or 2 too many and this might invalidate the test. 

 

Happy Monday Friends-

🙂

JenTheSchoolRN, BSN, RN

Specializes in School nursing.

3 hours ago, Jedrnurse said:

This is definitely a pain and a pain I have experienced. Have you heard of anyway of getting just an extra reagent bottle? My project coordinator said the only way is to order full kits...

Yep, that is the only way, which stinks. I think they need to repackage 2 bottles of regent in those kits, honestly. 

3 hours ago, Cattz said:

Could it be that it is measured out for 6 drops per test and this may have something to do with the bottle of reagent not being enough to last for the whole box? Thank you, you have taught me something. I have been afraid that I would accidentally let a drop or 2 too many and this might invalidate the test. 

 

Happy Monday Friends-

🙂

nope! If anything, it helps me more to put on an extra drop of two to make sure enough liquid gets into the swab slot so the test can get read at all.