Coronavirus testing

[Skimpot flyer]

Lockdown recipe:
1. Show the public - via mass testing - that persons displaying no symptoms can pass-on the virus
2. Add doubt to the mixture: i.e. if a person feels perfectly healthy (and actually is), they could be an asymptomatic carrier
3. Use this logic to place EVERYBODY under house arrest lockdown light (Tier 3)

 

[jtuk]

Here's a good one on testing, which more or less shows exactly what we've all been saying about PCR being terrible for months:

https://twitter.com/TiceRichard/status/1328666061848375317

Lateral Flow Tests, agreed by PHE as 99.7% accurate, show 80% fewer cases in Liverpool v. Govt standard PCR tests. First major comparison, shows whole Govt strategy possibly based on flawed data

 

[SteveM70]

I needed to get a test late last week. Found out about 9am Friday when I joined the dots between what I thought were borderline COVID-style symptoms and my son, who’d been at mine the weekend before, finding out one of his housemates had a positive test.

Went online at 9:30 and booked a test at a drive through centre at 11:00

Self-administered the test without any problems and was home by 11:45

Got the result by text and email at 6:45 on Saturday.

So, it clearly can work.

And my test was negative, by the way

 

[trebor79]

Here's a good one on testing, which more or less shows exactly what we've all been saying about PCR being terrible for months:

https://twitter.com/TiceRichard/status/1328666061848375317

I saw that too. However, it's nonsense for a couple of reasons.
Firstly, those booking a test because they had symptoms were sent to specific test centres, and I believe most of those were using the PCR test. That accounts for the larger proportion of positives. Unless you subject the exact same.cohort of people to both tests at the same time, you can't make any valid comparisons like this.
Secondly, I think he's getting muddled over specificity and sensitivity. It is widely understood that the LFT is less sensitive than the PCR, so that's another reason you might expect to see more positives in the PCR set.

 

[DustyBin]

I’m not sure if anybody else has seen this? It supports what some people have been claiming regarding the reliability of testing:

https://www.uticaphoenix.net/2020/11/17/portuguese-appeals-court-deems-pcr-tests-unreliable/

On November 11, 2020, a Portuguese appeal court ruled it was unlawful to quarantine people based solely on a PCR test.

The court stated, the test’s reliability depends on the number of cycles used and the viral load present. Citing Jaafar et al. 2020, the court concludes that “if someone is tested by PCR as positive when a threshold of 35 cycles or higher is used (as is the rule in most laboratories in Europe and the US), the probability that said person is infected is less than 3%, and the probability that said result is a false positive is 97%.” The court further notes that the cycle threshold used for the PCR tests currently being made in Portugal is unknown.

This case concerned the fact that four people had been quarantined by the Regional Health Authority. Of these, one had tested positive for COVID using a PCR test; the other three were deemed to have undergone a high risk of exposure. Consequently, the Regional Health Authority decided that all four were infectious and a health hazard, which required that they go into isolation.

The court’s summary of the case to rule against the Regional Health Authority’s appeal reads as follows: “Given how much scientific doubt exists — as voiced by experts, i.e., those who matter — about the reliability of the PCR tests, given the lack of information concerning the tests’ analytical parameters, and in the absence of a physician’s diagnosis supporting the existence of infection or risk, there is no way this court would ever be able to determine whether C was indeed a carrier of the SARS-CoV-2 virus, or whether A, B and D had been at a high risk of exposure to it.”

In the US, the FDA’s instructions for PCR testing recommends a threshold of 40 cycles for a specimen to be considered positive. See page 35 of the instructions.

At 25 cycles the original material has been multiplied 33,554,432 times.

At 30 cycles the original material has been multiplied 1,073,741,824 times.

At 40 cycles the original material has been multiplied 1,099,511,627,776 times.

As you can see there is quite a difference in magnification at various cycle thresholds.

It is also important to remember PCR was invented as a way to create copies of genetic material. Its was never intended to be a diagnostic tool.

 

[trebor79]

It is also important to remember PCR was invented as a way to create copies of genetic material. Its was never intended to be a diagnostic tool.

Meh. That's like saying the computer was invented as a way to automate projectile trajectory calculations and codebreaking, it was never intended to be used to discuss things in an electronic forum.
PCR amplifies the genetic material to a level at which it can be detected. If the primers are properly selected, it is extremely accurate - like 1 in a billion accuracy. You can't multiply what isn't there to start with.

It's a bit like having a library with a million books. We want to know if a particular book is in there. We could spend ages searching the library, and might miss it anyway. Or we could invent a process that will make copies of said book, and then we can look into the library when it's done it's work and see if there's a great big pile of books on the floor.
So, we need to tell the process what to look for. Let's say we want to find "Catch 22". The first work in Catch 22 is "It", the last word is "off". So we could ask out process to copy all books with first word "it" and last word "off". This would make copies of Catch 22, but also probably lots of other books as these aren't very specific phrases.
So let's instead make copies of all books containing the first and last sentences of Catch 22 "It was love at first sight" AND "The knife came down, missing him by inches, and he took off." It is highly improbable that any other books have the exact same first and last sentences, so if we run our multiplication process and end up with a great big pile of books on the floor, we can be very sure that "Catch 22" was in the library.
This is how PCR works, and why it is useful for diagnostics.

 

[DustyBin]

Meh. That's like saying the computer was invented as a way to automate projectile trajectory calculations and codebreaking, it was never intended to be used to discuss things in an electronic forum.
PCR amplifies the genetic material to a level at which it can be detected. If the primers are properly selected, it is extremely accurate - like 1 in a billion accuracy. You can't multiply what isn't there to start with.

It's a bit like having a library with a million books. We want to know if a particular book is in there. We could spend ages searching the library, and might miss it anyway. Or we could invent a process that will make copies of said book, and then we can look into the library when it's done it's work and see if there's a great big pile of books on the floor.
So, we need to tell the process what to look for. Let's say we want to find "Catch 22". The first work in Catch 22 is "It", the last word is "off". So we could ask out process to copy all books with first word "it" and last word "off". This would make copies of Catch 22, but also probably lots of other books as these aren't very specific phrases.
So let's instead make copies of all books containing the first and last sentences of Catch 22 "It was love at first sight" AND "The knife came down, missing him by inches, and he took off." It is highly improbable that any other books have the exact same first and last sentences, so if we run our multiplication process and end up with a great big pile of books on the floor, we can be very sure that "Catch 22" was in the library.
This is how PCR works, and why it is useful for diagnostics.

Thanks, I think I undertand what you're saying, i.e. there MUST be some viral load present, however small, for the PCR test to detect it? So why then, did the court reach the conclusion it did? Is it effectively saying that a small enough viral load doesn't constitute an infection?

 

[MikeWM]

Thanks, I think I undertand what you're saying, i.e. there MUST be some viral load present, however small, for the PCR test to detect it? So why then, did the court reach the conclusion it did? Is it effectively saying that a small enough viral load doesn't constitute an infection?

This article may help explain

https://www.cebm.net/covid-19/infectious-positive-pcr-test-result-covid-19/

PCR detection of viruses is helpful so long as its limitations are understood; while it detects RNA in minute quantities, caution needs to be applied to the results as it often does not detect infectious virus.

Effectively, if you set the cycle threshold too high, you're going to identify people who are actually no longer infected or infectious (and/or never were in the first place), which presumably is the only point in actually testing someone.

It is also true that the inventor of the PCR technique didn't intend it to be used in this way and was indeed critical of such use - but of course that doesn't, in and of itself, mean it shouldn't be.

 

[trebor79]

Thanks, I think I undertand what you're saying, i.e. there MUST be some viral load present, however small, for the PCR test to detect it? So why then, did the court reach the conclusion it did? Is it effectively saying that a small enough viral load doesn't constitute an infection?

Sorry for the typos, but yes you've understood correctly. If there is no target RNA present the rtPCR test will not come back positive.
As for what the court decided, I haven't looked into it so can't really comment.
It is perfectly possible that somebody would test positive but be asymptomatic, for various reasons. This is the biggest problem with testing asymptomatic people. As far as I know, it is not proven that asymptomatic people can easily spread the virus to others.

 

[DustyBin]

Sorry for the typos, but yes you've understood correctly. If there is no target RNA present the rtPCR test will not come back positive.
As for what the court decided, I haven't looked into it so can't really comment.
It is perfectly possible that somebody would test positive but be asymptomatic, for various reasons. This is the biggest problem with testing asymptomatic people. As far as I know, it is not proven that asymptomatic people can easily spread the virus to others.

Again, thanks (I hadn't noticed the typos!).

 

[david1212]

Lockdown recipe:
1. Show the public - via mass testing - that persons displaying no symptoms can pass-on the virus
2. Add doubt to the mixture: i.e. if a person feels perfectly healthy (and actually is), they could be an asymptomatic carrier
3. Use this logic to place EVERYBODY under house arrest lockdown light (Tier 3)

Don't give SAGE etc any more ideas .....

 

[david1212]

I've dug up this old thread as to me the best place for the report below. If a moderator thinks better elsewhere please move.

Thousands of UK Amazon workers given false Covid test results

Thousands of UK Amazon workers given false Covid test resultsExclusive: officials say the employees tested negatively but were sent notifications telling them to self-isolate Coronavirus – latest updatesSee all our coronavirus coverage An Amazon fulfilment centre in Swansea. The company has a...

uk.news.yahoo.com

Thousands of Amazon workers received the wrong Coronavirus test results after a mistake meant they were given inaccurate information by test and trace.
The Guardian understands that 3,853 staff members at the online retailer received an erroneous result. Officials said they had tested negatively but received notifications to say they had tested positive and asking them to self-isolate.
The Department of Health and Social Care (DHSC) said it had been resolved in a day but those working for the “world-beating” service that tracks down those who may have been infected with the virus said they were still dealing with the fallout.
One test-and-trace worker said: “The tests, as far I can tell were good, but what people were told about their results is wrong.”

 

[dk1]

Had to self isolate for 7 days after my phone ‘pinged’ the Thursday before last & ironically that same evening my weekly COVID test results came through as negative although that makes no difference. Makes you even more keen to get the results back this week, which where as expected negative once again.