Coronavirus - how is it/has it affected you?

Ethan

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:unsure:
Were you replying to me, what were you saying?

Oh, musta pressed the wrong button.

Let's wrap this up. With Covid LFTs, in my view, sensitivity and specificity are such that it is reasonable to accept a positive LFT as adequate confirmation of infection, as it approximates well enough to PPV.

You are right on the 50/50 prevalence, of course. If the true prevalence is 50%, though, hardly worth bothering testing.
 

SwingsitlikeHogan

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You are mixing up positive predictive value and sensitivity.
See the article in the link above.

If you take 100 people 50 with covid and 50 without and test them with a method that says they all have covid you will have positively identified everyone with Covid so you have correctly identified everyone with the disease. ie the sensitivity is 100%
On this…are different makes of LFT of different sensitivity? When I was testing couple of weeks back I had a strong +ve one day with one brand and the next day with a different brand i was only very faintly +ve.
 

SwingsitlikeHogan

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Probably. Repeat testing also can include variable technique and sampling variability.
Hmmm…so could possibly have tested -ve sooner than I did had I used one brand rather than another…that feels a bit unsatisfactory either way...ah well…maybe as we don’t have to test unless symptomatic I won’t bother fretting about it.
 

Backache

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On this…are different makes of LFT of different sensitivity? When I was testing couple of weeks back I had a strong +ve one day with one brand and the next day with a different brand i was only very faintly +ve.
Not sure what the differences are, my memory is that they were around 70% sensitive when compared with PCR but around 99.9% specific on Porton Down testing whether other brands have tested differently don't know but I imagine procurement would ensure that they are all reasonable. They are not really meant to be quantative so the result is positive or not, a slightly fainter line is still positive.
 

SwingsitlikeHogan

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Not sure what the differences are, my memory is that they were around 70% sensitive when compared with PCR but around 99.9% specific on Porton Down testing whether other brands have tested differently don't know but I imagine procurement would ensure that they are all reasonable. They are not really meant to be quantative so the result is positive or not, a slightly fainter line is still positive.
indeed how I interpret even a faint test show. Plus my understanding has always been that LFTs only really provide an indication of the prevalence of the virus in any tested population given a statistically significant sample size. A test taking by an individual gives an indication but certainly nothing like 100% certainty one way or the other - so in my understanding it has always been the case that rather too much faith has been placed on an LFT to provide a definitive individual infection status.
 

rudebhoy

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I tested positive last Friday. My understanding was I had to isolate then have 2 negative tests on Days 5 and 6 before venturing back out. However looking at gov.uk, that seems to no longer be the case? Is that right? Do I just start going about life as normal as soon as I don't have symptoms?

I'm in England btw.
 

Backache

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indeed how I interpret even a faint test show. Plus my understanding has always been that LFTs only really provide an indication of the prevalence of the virus in any tested population given a statistically significant sample size. A test taking by an individual gives an indication but certainly nothing like 100% certainty one way or the other - so in my understanding it has always been the case that rather too much faith has been placed on an LFT to provide a definitive individual infection status.
Absolutely, if you have not had covid the chances of false positives if tests are done properly are probably very low indeed The positive rate on PCR the ONS survey fell to 0.02% after the first wave and as this must be the sum of the false positives and true positives and there was certainly some covid, false positives are probably exceptionally low. However judging whether or not you are likely to be infectious from a single swab with a non quantative test at a single point of time in the infection is always going to involve a degree of guesswork.
 

Backache

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I tested positive last Friday. My understanding was I had to isolate then have 2 negative tests on Days 5 and 6 before venturing back out. However looking at gov.uk, that seems to no longer be the case? Is that right? Do I just start going about life as normal as soon as I don't have symptoms?

I'm in England btw.
There are rules and there is what is sensible, you are clearly likely to be a potential source of infection to others, personally I would take lateral flow tests and would wear a mask initially if I could not take them.
 

rudebhoy

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There are rules and there is what is sensible, you are clearly likely to be a potential source of infection to others, personally I would take lateral flow tests and would wear a mask initially if I could not take them.
I get what you are saying. Reading the current guidelines, I could go out and about quite happily the day after a positive test which is just nuts.

I will have isolated for 5 days by tomorrow. I don’t have any symptoms now. I’ll do a test anyway tomorrow and if it’s clear, I’ll go back to golf on Thursday.
 

Foxholer

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I get what you are saying. Reading the current guidelines, I could go out and about quite happily the day after a positive test which is just nuts.

I will have isolated for 5 days by tomorrow. I don’t have any symptoms now. I’ll do a test anyway tomorrow and if it’s clear, I’ll go back to golf on Thursday.
Indeed, that seems nuts to me too - but perhaps not to some!
The guidance (here: https://www.gov.uk/guidance/people-...o-if-you-have-a-positive-covid-19-test-result) still states 'try to stay at home and avoid contact with other people for 5 days after the day you took your test' and to be careful for a further 5 days. Whether the further LFT shortens that period, I'm not certain, so would mask-up and take particular care around vulnerable folk for that period.
 

rudebhoy

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Indeed, that seems nuts to me too - but perhaps not to some!
The guidance (here: https://www.gov.uk/guidance/people-...o-if-you-have-a-positive-covid-19-test-result) still states 'try to stay at home and avoid contact with other people for 5 days after the day you took your test' and to be careful for a further 5 days. Whether the further LFT shortens that period, I'm not certain, so would mask-up and take particular care around vulnerable folk for that period.

If the test is negative, I'll be playing Thursday, but will avoid the clubhouse and any other indoor settings for the next week or so.
 

Swinglowandslow

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Indeed, that seems nuts to me too - but perhaps not to some!
The guidance (here: https://www.gov.uk/guidance/people-...o-if-you-have-a-positive-covid-19-test-result) still states 'try to stay at home and avoid contact with other people for 5 days after the day you took your test' and to be careful for a further 5 days. Whether the further LFT shortens that period, I'm not certain, so would mask-up and take particular care around vulnerable folk for that period.

Yep!
 
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