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

Hay fever is odd, as you need to find which pollen you are allergic to.

Have had hay fever symptoms in the past and not the same time of year so never figured out what pollen it was. A doc did mention that pollution can increase sensitivity to pollen. First hit on google

Pollutants such as nitrogen oxides and ozone can attack the pollen grains, bursting them open and releasing more of the highly allergic proteins that trigger hay fever. Ozone, nitrogen dioxide and sulphur dioxide pollution also attack the membranes in the respiratory tract, making people more susceptible to the pollen

My takeaway is that the lateral flow are almost worthless.

They are the best test we have.

EDIT: as an initial rapid test, that does not require a lab, it is the best we have.

The PCR is understood to be better I thought?

PCR gives a more accurate result of virus bits being present in the sample (putting aside all that specificity / sensitivity stuff ) but needs a lab and time.

Lateral flow is less accurate but better than nothing. On the other hand it's perhaps worse than nothing as a negative result gives a false sense of security....

Sorry wasn't clear, as an initial rapid non lab test, it is the best we have.

Lateral flow and PCR tests are two completely different tests. PCR is thousands of times more sensitive than a LFD.

PCR test will pick up on an absolutely miniscule amount of the virus. Lateral flow is testing for levels that would indicate someone is infectious with the virus.

Yes, ideally, everyone should get a PCR test but that's just not practical. You need a lab and therefore they take time.

The lateral flow test is better than nothing, but people shouldn't take a negative LFD test as equivalent to a negative PCR test.

Even with a negative PCR test you should consider the consequences of your actions. Have a negative PCR test and then spend half an hour inside somewhere (pub, train, a friend's house) and you're now back in unknown territory.

Have a negative PCR test

Haven't done that yet.

and then spend half an hour inside somewhere (pub, train, a friend's house)

Haven't done any of them for over a year, mind you.

Interesting nuances I hadn't appreciated.

In our case, youngest was snotty at 9am and 2pm, so it all seems a bit odd to me. So much with this stuff is an absolute minefield.

With covid having a fair few able to spread it without showing symptoms, lateral flows are useful for quick, widespread testing for picking up and reducing some of that, normally you'd get a PCR after showing positive on a lateral, like a pre test test, showing symptoms is another decent test for going to get a test.

Had anybody done an antibody test after having had confirmed covid.

In our case, youngest was snotty at 9am and 2pm, so it all seems a bit odd to me. So much with this stuff is an absolute minefield.

My 11yo has had a sore throat, runny nose, bit of a cough for 2 weeks. No history of hayfever.

PCR test (as part of the ONS testing study) came back negative. Lateral Flow test yesterday was negative (we did one as we were visiting some elderly friends, and also going to a garden party).

(If we weren't part of the ONS study we'd have booked PCR tests because of her symptoms.)

Some times a cold is just a cold, but it's worth checking especially as the lateral flow tests are free and easy to do. We use them occasionally to rule out possible asymptomatic infections before visiting others.

3 weeks of school to go, really hoping they can all stay in there to the end, daughter's primary has managed not to have any whole classes out yet although a couple of classes at each of the nearby primaries have popped.

Had to chase daughter's test yesterday morning - 'sorry, nothing here, we'll have to chase it up with the lab and someone will get back to you within 24 hours' - and got the negative result first thing this morning. So that's Wednesday evening to Monday morning for a result; guess the system's under a fair amount of pressure?

Now to desperately try and catch up on the work I'm behind on...

You are correct.

Any chance you could elaborate on this a bit? A bunch of my non medic friends have decided that lateral flow tests are worthless so don't bother with them any more however when i look for research on their effectiveness all I can find is info saying that although they are flawed, false positives are rare but they are better than nothing.

Any chance you could spell out why they are worthless and that we shouldn't bother with them in laymans terms?

My Mum is double vaccinated but super vulnerable to Covid,. I'm isolating for a week before I see her and taking a few LFTs during that week...should I not bother?

My understanding is one of this issues with them is that all the effectiveness data published around them relates to them being used in the context of people with symptoms and they are reasonably accurate when used by people showing symptoms to confirm if it is covid or not.

What they weren't designed for is identifying people with asymptomatic cases, so being used on mass by people with no symptoms is questionable as they are far less sensitive than a PCR test which will pick up miniscule amounts of virus.

I, like you have used them before visiting a very vulnerable relative but the challenge is that the negative lateral flow test could give false confidence that you aren't infectious and people might then not follow the other precautions (mask, space, high ventilation areas etc.). You sound like me and sensibly cautious. I avoided contact with others a week+ before before visiting and took the test as an extra precaution on top. Two weeks ago I went to the pub to watch England/Scotland and had friends who took a LFT the next day which came back negative and then went on to visiting friends,family attending other events the same weekend which I wouldn't of dreamed of and this is due to the test giving them overconfidence with the negative result. Two days later one of them was contacted by track and trace as a close contact with someone they had come in to contact with on the day we went to the pub and had to isolate. A PCR confirmed them negative but it could just of easily gone the other way.

I, like you have used them before visiting a very vulnerable relative but the challenge is that the negative lateral flow test could give false confidence that you aren't infectious and people might then not follow the other precautions (mask, space, high ventilation areas etc.)

Makes sense. But I understand them as being a useful tool if you use them wisely and in the context of all other measures rather than making them useless.

I have added a bit more anecdote as an example of how they can be used poorly by otherwise sensible people.

Maybe I'm being too pedantic as ever. If the majority of people who use them don't understand what a negative LFT actually means then perhaps they are useless from a public health perspective.

And in my test case of one, it seems a lateral flow did not detect covid at 9am on Saturday in a snotty 6 year old, but a PCR did at 2pm. Since then, she had a temperature on Sunday and has woken today with a cough.

We could have accepted the LFT and as a household carried on our business assuming it was just a cold (as has been going round her class). Instead we're now on total lockdown.

My hunch is that they are just not sensitive/accurate enough.

That is the main criticism I have read, they were never meant for the use the way our Government has chosen deploy them and it potentially risks people becoming over confident and dispensing with the other precautions

This is a fun article on Bayes and how it impacts the LFT, which again, I am guessing the majority of LFT users wouldn't take in to account when assessing their result:
https://www.theguardian.com/world/2021/apr/18/obscure-maths-bayes-theorem-reliability-covid-lateral-flow-tests-probability

Last week's cases per 100k in my borough, having risen slowly but steadily from ~15 to ~60 for the last few weeks, and hovered around 50-60 for a while:

date: "2021-06-29"
newCasesBySpecimenDateRollingRate: 101.7

date: "2021-06-28"
newCasesBySpecimenDateRollingRate: 92.4

date: "2021-06-27"
newCasesBySpecimenDateRollingRate: 76.1

date: "2021-06-26"
newCasesBySpecimenDateRollingRate: 68.3

date: "2021-06-25"
newCasesBySpecimenDateRollingRate: 62.6

date: "2021-06-24"
newCasesBySpecimenDateRollingRate: 60.2

date: "2021-06-23"
newCasesBySpecimenDateRollingRate: 63.2

So Javid's line is to just live with it from now on and accept numbers will rise?
Case numbers are going to be insane over the next couple of months and beyond.

I get that equitable global vaccine distribution makes it hard to argue that we should start vaccinating kids now, but it seems so immoral to be unleashing it on them by reducing restrictions further, with things how they are already.

a lateral flow did not detect covid at 9am on Saturday in a snotty 6 year old, but a PCR did at 2pm

That is expected. A PCR might be positive on days 2-12 after an infection on day 0. A LFT is more likely to be positive around days 5-8 (or similar).

Where an LFT might add value is if someone is asymptomatic. There is also apparently some correlation between shedding enough virus to be likely to infect someone else and an LFT positive test.

If you and your daughter are up for some experimentation you could lateral flow test you and your family every day for the next week or so. Would be interesting to see when, if ever, they are positive.

Very good!

My hunch is that they are just not sensitive/accurate enough.

True in terms of an individual test compared with PCR. But you need to look at the wider countrywide picture.

The UK labs just would not be able to cope with everyone doing a PCR test instead of using a LFD.

If you have symptoms then you go straight to PCR:-

https://www.gov.uk/order-coronavirus-rapid-lateral-flow-tests

"
Do not use a rapid lateral flow test if you have COVID-19 symptoms. Get a PCR test and self-isolate, even if symptoms are mild.
"

If you don't have symptoms you use a LFD, if that comes back positive you back it up with a PCR.

If the country had the capacity to do PCR tests for everyone that wanted one, even when they had no symptoms then that would be much better, but that lab capacity simply does not exist.

LFDs are useful as they can be done at home, can be mass produced and don't require any lab time.

Without LFDs we'd need to be in stricter lockdown, or be extending the existing lockdown for longer.

Thanks - interesting. The only thing I can't get my head around is how if she had a runny nose because those were her visible first symptoms of covid, how her snot did not contain enough virus to show up. To me, that seems a serious shortcoming as we could easily be living in blissful ignorance if not for our belt and braces approach.

I'm very tempted to do more LFDs, but don't think the misses wants me running an experiment on her at this moment. She's stressing big time already.

This is a fun article on Bayes and how it impacts the LFT, which again, I am guessing the majority of LFT users wouldn't take in to account when assessing their result:

https://www.theguardian.com/world/2021/a­pr/18/obscure-maths-bayes-theorem-reliab­ility-covid-lateral-flow-tests-probabili­ty

That was written in April when the infection prevalence was 1 in 340. Happy days! We are way higher than that at the moment so an LFT positive is unlikely to be false.