Chat about Novel Coronavirus - 2019-nCoV - COVID-19

[Catching up]

Thanks (and others who responded). It does seem a very mixed message around LFDs at the moment.

My guess is that the "don't test with lateral flow within 90 days of positive PCR" advice is just a form of chinese whispers. It may have started with "don't test with PCR again within 90 days of positive PCR" (which is sensible), that was changed to "don't test within 90 days of positive PCR", and then a subsequent change moved the "test" to "test with lateral flow or PCR". Who knows. It may also have been political in that they were worried that testing care home workers, NHS staff or school staff within 90 days of a positive PCR might mean they had to isolate again, which they couldn't cope with en masse, and so they tweaked the guidelines to avoid that situation (even though latent lateral flow positives aren't anywhere near as common as latent PCR positives due to the vastly different sensitivity of the tests.)

Just sent my daughter off to school (in full school uniform) solely to do a lateral flow test and then come home. I can see why they're doing them this way, it guarantees that it is being done (rather than parents saying they are doing them) and hopefully ensures it is being administered properly as it is witnessed (albeit by non-medical professionals). Also a bit odd as she had to do a lateral flow test at home before coming in, just for good measure, but I guess that will help identify any parents who claim they're doing the tests at home but aren't.

Back on subject though, two of my daughter's friends (Y7 so 11/12 years old) had tested positive (by PCR) 3-4 weeks ago and initially they'd been told they didn't need to come in for these latest LFD tests today, but that changed a few days ago and they're all going in.

It does make sense (to me at least). Irrespective of the politics and other limitations, if you're blowing positive on a LFD then there's a very good chance that you've got a high enough viral load for you to be actively infectious. Just because you first tested positive 10 days ago doesn't really change this. Allowing people to go out into the world when they are still blowing positive on an LFD 10 days later is quite bonkers in my opinion. If it had happened to my daughter (she stopped blowing positive on LFD 8 days after the confirmatory PCR and with 2 days of isolation left to go) I'd like to think we'd have continued to isolate at home for a few more days until we saw a negative LFD. (Obviously this gets trickier for people who, for whatever reason, continue to test positive for much longer than 10 days.) It was also easy for us to do as neither of us needed to go out of the house for any reason.

Also remember that you'll hear the anecdata about odd test outcomes (people testing positive on one and negative on the other) much more often and much louder than all of the hundreds of thousands of tests that perform as expected each and every day. Between the three of us in our house we've had ~60 PCR tests and probably 100 LFD tests. The only positives were when my daughter was definitely infected, and we saw a pretty standard progression in LFD tests as that infection subsided. Unfortunately she missed the two subsequent PCR tests from the ONS so we've no idea if she would have tested positive on those once the LFDs had cleared up, she didn't test positive on PCR when she was next tested 12 weeks from the original infection. She also never got round to doing the ONS antibody test, and has now been jabbed.

Irrespective of the politics and other limitations, if you're blowing positive on a LFD then there's a very good chance that you've got a high enough viral load for you to be actively infectious. Just because you first tested positive 10 days ago doesn't really change this. Allowing people to go out into the world when they are still blowing positive on an LFD 10 days later is quite bonkers in my opinion.

Source? I've not seen any evidence for that being the case, but have seen reports saying it's not, and the link between being contagious and having viral load is unknown (if there is one). The reason people have previously been asked to isolate for a period of time, rather than until a negative test result, is because the likelihood of being contagious drops significantly with time regardless of positive tests which can last longer.

6 days on from my partner's positive LFT - she's still testing positive but the line is now fading out (it was very strong yesterday), I'm still negative but as of yesterday/today have a slight runny nose and something happening to my throat. Wouldn't describe it as a cough or soreness - just a bit dry I suppose. I thought I'd test positive today on an LFT but not a trace of it.

This has some (and links to sources):-

https://www.gov.uk/government/publications/lateral-flow-device-performance-data/key-points-summary-asymptomatic-testing-for-sars-cov-2-using-antigen-detecting-lateral-flow-devices-evidence-from-performance-data-october-2020-to-m

"
Infectiousness can be broadly related to viral load (how much virus can be found in a test sample). Those with a high viral load are most likely to be infectious, therefore it is particularly important to identify those with high viral loads. These people are most likely to be in the infectious and transmissible stage of the virus.
"

(Obvious possible bias is obvious.)

Useful twitter bot

https://twitter.com/LFT_alert/

I just try a few times a day when we need some (generally when we crack open the 2nd last pack) as we get through about 8 tests a week here (more if there's an after work cheese and wine party at the weekend) but it is easy for me as I sit at a computer for most of the day and have a reasonable memory.

I'm expecting MiniGB to come home with a pack from school today which lessens the ordering load but that doesn't go far - I think the school are still recommending 3 a week for her.

I've scowled at friends who mention they've been stockpiling them. FFS!

Source?

The official usage scenario for LFTs in the UK is to catch asymptomatic infections, while you are in the most contagious phase. That scope has crept to the point that people are using them for symptomatic Covid.

https://www.ucl.ac.uk/news/2021/oct/lateral-flow-tests-detect-most-people-risk-transmitting-covid-19

“It is most likely that if someone’s LFT is negative but their PCR is positive then this is because they are not at peak transmissible stage.”

can be broadly related

Doesn't sound definitive to me.

You claimed people testing positive after ten days should remain in isolation because they will still be contagious. I was curious if you had evidence for this.

edit Quick google and I can't find any source that claims a positive test after 10 days isolation (assuming your symptoms have improved) is indicative of someone still being contagious. I'm not denying the possibility, but just haven't seen that claim made.

I have no idea why you've posted this @ me.

Doesn't sound definitive to me.

I thought I'd couched my comments with enough speculative terms to make it obvious that it was my opinion and not fact. "very likely", "in my opinion", "very good chance", etc.

The source I linked to says the correlation (however strong it is) is between viral load and infectiousness. How long you've been at that stage doesn't seem to come into it.

Do you think it's a good idea that people still blowing positive on a LFD after 10 days of isolation following a confirmatory positive PCR test should be allowed to end isolation and go back to commuting/work/socialising/etc?

(I don't think it's a good idea, but that's just my opinion, I know of no evidence to support/challenge this.)

I thought I'd couched my comments with enough speculative terms to make it obvious that it was my opinion and not fact. "very likely", "in my opinion", "very good chance", etc.

You also said it's "quite bonkers" for people to leave isolation after 10 days without a negative. So your terms were clearly loaded in multiple ways. I think it's fair to call them out.

The source I linked to says the correlation (however strong it is) is between viral load and infectiousness.

There is obviously a correlation between viral load and being infectious at some point. You cannot be one without the other. The question is about causation. I.e., is there a causal relationship between a positive test after 10 days and being contagious.

How long you've been at that stage doesn't seem to come into it.

Right. And that was the claim I wanted info on.

Do you think it's a good idea that people still blowing positive on a LFD after 10 days of isolation following a confirmatory positive PCR test should be allowed to end isolation and go back to commuting/work/socialising/etc?

Yes, because that's what, as far as I can tell, the science has said should happen. That is, there is not a clear link between a 10 day positive and being contagious. In fact, the link that does exist is between 10 days post first symptoms/positive test and not being contagious. This is probably why these are the rules that are in place in pretty much every country I know of (with some variations in amount of time). The only time tests seem to play a role is when one can exit isolation early.

(I don't think it's a good idea, but that's just my opinion, I know of no evidence to support/challenge this.)

It's funny how some opinions without evidence on here are a-okay (usually opinions about people being locked up in flats for long periods of time), but others are not. @amey made a good point on this a couple of weeks ago that was pretty much ignored.

https://amp.theguardian.com/world/2022/jan/03/uk-covid-test-distributor-shut-christmas-25m-kits

My guess is that the "don't test with lateral flow within 90 days of positive PCR" advice is just a form of chinese whispers.

No idea about the logic or the rule but this was the reason given to the GF by the school (academy) that she did not have to test and the school would not issue LFT tests until the 90days had passed.

But this was the beginning of last year.

Fair enough, opinions and arseholes and all that.

But I think the "isolate for 10 days" rule is just a product of a need for simplicity that is a cultural limitation of the UK population[1]. Anything more complex than that is unlikely to be as effective due to people getting confused, ignoring things or just coming up with another reason why they think it doesn't apply to them. I personally think it still lets quite a few people out into the world who are still infectious (it's unlikely to be zero, and no-one here would be able to quantify whether it is just a handful or many more than that so there's little merit in any debate on the magnitude of the problem).

My point is, I don't doubt that "isolate for 10 days" is a high effective strategy, as evidenced by the fact that many many countries follow the same rules, but more effective strategies are just too complex and could quite possibly just lead to lower overall compliance (and therefore be a retrograde step).

1. Some countries are a bit more flexible in some respects. See France and the different speed limits on Autoroutes depending on the weather.
   

My cousin had covid 2 weeks before Christmas and then his Dad cancelled meeting up with him due to him speaking to his doctor friend who suggested if you wanted to be extra cautious 20 days - a figure plucked out of the air?

Frankly ridiculous IMO, if you're aiming for zero risk then you're gonna have a miserable time.

I'd rather meet someone who tested positive 10 days ago than a person who hasnt tested positive 10 days ago

At my work you have to present negative LFT to access the building. I don't see any rules for 'still testing positive LFT more than 10 days after PCR positive' - wonder what happens if there's someone like @Fox - just don't come in to work for a couple of months?!

wonder what happens if there's someone like @Fox - just don't come in to work

Then you dont have to hear how wonderful Walthamstow is

cc/ @chrisbmx116

It's not about aiming for zero risk though is it?

My attitude to how much I socialise and who with would be quite different if I was mid 70s rather than mid 40s. The risk of catching it is not much different (given both cohorts are triple jabbed), but the possible outcomes are quite considerably different.

I'm not surprised my 80yo parents didn't want any of their children or grand-children to visit them in person over Christmas, they're happy with the odd Zoom call until things have settled down a bit.

I'd rather meet someone who tested positive 10 days ago than a person who hasnt tested positive 10 days ago

Interesting thought experiment. I'm not sure how I'd answer that question (for myself) or for elderly relatives, but then for them I'd rather someone tested themselves on the day and based their decision on that (plus a bit more context).

To push the question in a different direction, if you had to choose someone to go visit elderly relatives would you rather it was:-
a) A person who tested positive 10 days ago and was still testing positive on a LFD
b) A person who tested positive 10 days ago and was no longer testing positive on a LFD

NHS say if you test positive on day 10, you can't return to work until a negative LFT is produced

I have seen other employers caveat it that if you have symptoms and are still testing positive after 10 days you can't return until a negative is produced

The 10 days is an arbitrary cut off for simplicity and that captures the vast majority of cases

https://www.valeofyorkccg.nhs.uk/seecmsfile/?id=4912

Seems this was proper guidance at some point.

Both admissions and patients in hospital in London seems to be stabilising well below the January 2021 level. Or are there issues with the data?

Thank you.

I have no idea why you've posted this @ me.

Because you asked for a source about LFTs and the link between positive test and contagiousness. Or have I become extremely confused?

Edit: ah, I see the confusion now. Sorry, thought you wanted a source about pos LFT indicating peak contagiousness.

So playing tennis gives you a medical exemption from a vaccine and you can still travel.

Now how is that going to play for us mere plebs? To me it will just fuel people resentment of having to be vaccinated.

Professional Sportspeople have had various exemptions from rules since very start of the pandemic. Poor optics, I agree, but not the first time.