# Covid cases drop by almost 13,000 over past week



## Amity Island (Jul 24, 2021)

Cases dropped by 12,899 from 48,553 to 35,654, which is very promising.

It will be interesting to see where this goes as restrictions were lifted this week.









						New daily covid cases fall 10k in a week but it's too soon to declare the third wave has peaked
					

Coronavirus infections may be falling from a high caused by mixing around the Euro 2020 tournament




					inews.co.uk


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## mikeyB (Jul 24, 2021)

Indeed, as restrictions have been lifted earlier this week, it won't be until another week or so whether the trend goes up or continues to reduce. Personally, I suspect it will be an increase.


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## Bruce Stephens (Jul 24, 2021)

mikeyB said:


> Personally, I suspect it will be an increase.


That seems to be the assumption, but it doesn't explain why there's a fall right now. Hypotheses include breakup of (some) schools, people doing more things outdoors (because of the hot weather), and a fall following the Euro 2020 rise.

(I don't think anyone thinks it's due to the recent issues with tests not being available which was my first thought. Apparently the Zoe app also shows a fall, so it looks like it's real.)


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## Northerner (Jul 24, 2021)

I think it's because there aren't enough people to count all the cases, as they are all self-isolating


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## Eddy Edson (Jul 25, 2021)

Northerner said:


> I think it's because there aren't enough people to count all the cases, as they are all self-isolating


A ping-anti-demic!


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## Bruce Stephens (Jul 25, 2021)

Bruce Stephens said:


> Apparently the Zoe app also shows a fall, so it looks like it's real.


I'm wrong. It showed a plateau last week but they think that's was a flaw. It's showing continued rise now except in Scotland (which is showing a fall).









						Hopes that wave of infections had peaked fade
					

The overall number of estimated cases is 60,019, which indicates that new cases are still on the rise in the UK.




					covid.joinzoe.com


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## Amity Island (Jul 26, 2021)

Bruce Stephens said:


> I'm wrong. It showed a plateau last week but they think that's was a flaw. It's showing continued rise now except in Scotland (which is showing a fall).
> 
> 
> 
> ...


Bruce, this is wierd. I just checked again this morning and cases still dropping dramatically.


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## Docb (Jul 26, 2021)

If there is a real diminution in infection levels then the number of negative tests should be increasing.  Could not find the data to check.  Anybody know if it is available?


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## Bruce Stephens (Jul 26, 2021)

Docb said:


> If there is a real diminution in infection levels then the number of negative tests should be increasing. Could not find the data to check. Anybody know if it is available?


I think test positivity is reported somewhere or other but only weekly for some reason. I think someone reported that it had been increasing which is what ourworldindata also shows. Still under 5% probably.

I don't think anyone reports the number of negative tests (or the number of people who test negative). Test positivity is the usual metric for whether you're doing enough tests or not and the usual cutoff is 5%, so we're still (just) under that.


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## Eddy Edson (Jul 26, 2021)

Bruce Stephens said:


> I think test positivity is reported somewhere or other but only weekly for some reason. I think someone reported that it had been increasing which is what ourworldindata also shows. Still under 5% probably.
> 
> I don't think anyone reports the number of negative tests (or the number of people who test negative). Test positivity is the usual metric for whether you're doing enough tests or not and the usual cutoff is 5%, so we're still (just) under that.


The govt dashboard shows it dropping back below 4% on a rolling 7 day basis:  https://coronavirus.data.gov.uk/ 

Testing down a bit but not as much as detections.


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## Robin (Jul 26, 2021)

The Government daily figures include the total number of tests, and the number of positive tests, but one is three days ahead of the other. I would expect the number of tests being done to drop sharply now we are in the school holidays, and pupils aren’t doing their twice weekly tests.
Edit. @Eddy Edson types faster than me, and has explained it better!


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## Eddy Edson (Jul 26, 2021)

Robin said:


> The Government daily figures include the total number of tests, and the number of positive tests, but one is three days ahead of the other.


Oh - I didn't notice that. Annoying!


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## Docb (Jul 26, 2021)

And if you dig a bit you will find it published as what you think is a cusum but some of it does not look like a cusum. Adds to the annoyance.


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## Bruce Stephens (Jul 26, 2021)

Robin said:


> I would expect the number of tests being done to drop sharply now we are in the school holidays, and pupils aren’t doing their twice weekly tests.


People are speculating that that might be part of the explanation. Cases are largely in young people and there's this large group of pupils suddenly not testing twice a week, so maybe we're just missing those (many of which will be asymptomatic so not rushing to get tested).

Presumably this Friday's ONS survey report will give more clues.


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## Docb (Jul 27, 2021)

Another thing.  Brain a bit fuggy this morning but have not sorted out in my mind exactly what this "covid cases" number actually counts.


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## Docb (Jul 27, 2021)

I was musing at a lot simpler level than that Amity.  

When it comes to PCR test accounting things should be straightforward.  You have an accepted protocol (whether its good, bad or indifferent is a different issue) and the tests are carried out in centralised labs and so data collation should not be an issue.  You know how many tests have been submitted and how many are positive.  The number of COVID cases found by this route can be established.  

Where I am unclear is with the lateral flow test which is not done in a centralised laboratory.  Do the results of those tests get included in the figures.  If so how?


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## Bruce Stephens (Jul 27, 2021)

Docb said:


> Where I am unclear is with the lateral flow test which is not done in a centralised laboratory. Do the results of those tests get included in the figures. If so how?


Those that are reported get counted, but they try to somehow not double count tests (since a positive lateral flow test gets you a PCR test). I'm not sure exactly how they're included in which figures.


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## NotPink (Jul 27, 2021)

Confused.com?


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## Bruce Stephens (Jul 27, 2021)

Amity Island said:


> I can say that until 2020, a "case" of anything usually meant you were suffering, in bed ill, had symptoms or were in hosptial as a result of having a "case" of something. Like a bad case of flu, food poisoning etc


There's a bunch of exceptions: all those things that are screened for. Like (to take an example at random) Type 2 diabetes: lots of people discover they're diabetic as a result of a routine blood test.

"Case" in the context of Covid-19 should be defined depending on context. For example on https://coronavirus.data.gov.uk/details/cases they say what they consider a case to be. And the ONS survey says that it's showing an estimate of the number of people who would test positive using the PCR test in the way that they're using it.

Who gets tested is an important variable. Mostly (for a while now) in the UK that's mostly been people with one or more symptoms. (Not exclusively, but mostly.)

(One factor which may or may not be significant is that the symptoms being used are apparently wrong now: people who're infected with the delta variant, especially those who are vaccinated, aren't likely to have any of the symptoms which you ought to have to get a PCR test. On the other hand, the common symptoms are _really_ common; testing everyone with a runny nose or who sneezes doesn't seem sensible in a Bayesian sense even if it was practical.)


Amity Island said:


> The PCR tests use such high cycle numbers, that one could basically find anything, any remnant of any past virus. From my understanding anything above 35 cycles (millions of duplicates) isn't worth relying on. It appears that most of the labs in the UK have been testing at 40 cycles (a trillion up cycles). The lower the number of up cycles, the more reliable the test result. So anything below 30 could be considered a reliable result.


That's not actually true, though, according to people who're familiar with PCR. See (for one of _many_ examples) https://www.mcgill.ca/oss/article/c...st-reliable-despite-commotion-about-ct-values
*Take-home message:*​- Some people claim, wrongly, that the PCR test for the coronavirus is useless because the so-called Ct values are too high and the test is picking up things that are not the coronavirus​- The PCR tests for the coronavirus that have been internally validated by public health agencies are actually very reliable​- Scientists cannot declare any result above a certain Ct value to be unreliable because Ct values are somewhat relative and must be interpreted by taking into account a variety of factors​
Additionally, in the UK we also do sequencing on a large proportion of positive cases.

It's entirely true that just because someone tests positive doesn't mean they're infectious. Or that they were or ever will be infectious. It's known that someone who's recovered from an infection can continue to test positive for a while (perhaps a long while). People work with imperfect information from imperfect tools, as always.


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## Amity Island (Jul 28, 2021)

Still dropping, pretty quickly too. Just 23,000 daily "cases" (whatever that means?) Fingers crossed this trend continues...


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## Docb (Jul 30, 2021)

Don't want to prolong this debate but I have had a look at the "daily cases" number to see if I can figure out what it means and I am finding it very difficult!  

If you go to the government dashboard and scroll down you will find a link which allows you to download the data.  There you might expect to find a set of files giving the number of tests done each day split into PCR tests and lateral flow tests and the number positive tests again split into PCR and lateral flow.  From those data you should be able to make an assessment of the proportion of tests that are positive, ensure that the data are not confounded by the test type and make some judgement of the extent of the virus in the population. If you check this out, you will find a long list of files but nearly all of them are processed data - very, very, difficult to get back to the raw numbers with any degree of confidence.  Calling the number published "daily cases" is pushing it a bit.

There is only one conclusion I can come to and that is one should be a bit wary when listening what is being said about the numbers, be it from the scientists or the conspiracy theorists, the politicians or the journalists, the amateurs or the pros.  Interpreting the data is a long way from straightforward and you can cut it to support any point of view that you want to put forward.

PS... the recent drop in daily cases seems to correspond with a drop in the number of tests done which seems to correspond with a drop in lateral flow tests, but I would not go as far as to suggest this correspondence amounts to a correlation.


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