If there's a link provided, it points to an Emergency Use Only instruction document for the CDC's SARS-CoV-2 PCR (July here, may be other versions) in which there's a comment: testing had to use a viral sequence made in the lab because didn't have *quantified* virus isolates

This whole misunderstanding (I'm being generous) hinges on the word "quantified". CDC researchers *had* cultured virus (see ) in January & March, but they didn't have a preparation of virus in which they knew number of infectious particles present. That's the quantified bit.

When you know how many infectious particles present, you can determine the limit of the sensitivity of the RT-PCR, in those same terms. Which is nice but not essential.
You can also do this using the same viral sequence target, prepared & quantified in the lab as RNA. They did

Now back to the bit about isolation of virus & the CDC. Yes, CDC scientists had grown virus in cell culture ("isolated" it; isolate called 2019-nCoV/USA-WA1/2020) which was acquired from a patient specimen Jan 20, 2020
https://wwwnc.cdc.gov/eid/article/26/6/20-0516_article [paper published in March]

The virus was later made available to other researchers via a commercial reagent supplier (catalogue number NR-52281).
https://www.beiresources.org/Catalog/animalviruses/NR-52281.aspx

There was also this study of US cases that isolated virus from multiple patients and sample types, reported in March 2020.
https://www.medrxiv.org/content/10.1101/2020.03.09.20032896v1

NOTE: I don't know the precise order of events, but virus *was* isolated available, the isolate was shared early, & is currently available
A shame diagnostics team didn't have access to quantified virus prep, because one was described in paper-perhaps a communications issue?

So, once again, this conspiracy theory is just that. It isn't factual but it is being used for all manner of fear-inducing, trust-eroding statements.
But its easily debunked because it's so wrong.

I know the follow-up from the hardcore belief and feelz cultists will be "but this isn't _purrrre_ isolation, it was grown in animal cells".
And they're right on the last part. It was grown using particular animal cells because they are permissive for the growth of the virus.

Contrary to the impression you might have, its not always easy to isolate a virus form a patient sample. And some viruses grow in cells that other viruses won't. And some are just too hard (or really hard) to isolate at all.

But the virologists - you know, the people with expertise in this stuff who have spent decades finding, learning about & growing viruses for study - are fine because this is how it's done. We could scrape cells from *your* airways (primary cell culture) and get them settled..

...into culture dishes & then infect them with someone else's sample, but they would soon die. And there is huge variability in collection of cells this way. And you can't keep doing it (you need lots of cells to do this work at scale) or the donor will bleed, develop scarring...

..and not come back for more! These cells we use are usually immortal in some way - they have cancer genes working to keep them dividing forever, or a virus has changed them & so on. So we can grow them up in huge numbers and have them ready for receiving lots of samples

(each patient sample gets its own batch of cells).
But why culture at all? Because viruses are tiny. About 100 million (100,000,000) can fit on the surface of a pin head (200nm virus, 2mm pin head). It's much easier to find & examine virus particles using electron microscopy if

you grow more of them first (you *can* view them direct in patient samples if decent viral load, but can be in the presence of lots of other crud making it messy).
It's also a simple way to produce enough of the virus to come back for future studies like animal infections or

some vaccines or as a control for use by hundreds of labs. One patient sample simply isn't enough.
Similarly we need PCR-based methods to amplify up the viral genetic material first, so we can get enough to sequence its unique code.

We *know* culture can introduce slight genetic changes (not at the level that calls into question the nature of the virus though!) but we can see & account for such changes by sequencing virus from the clinical sample first then comparing the sequence to the cultured version.

Most SARS-CoV-2 sequencing is performed from patient material, not cultured isolates. So that issue's already avoided.
One example of this is that 2019-nCoV/USA-WA1/2020 US variant which was sequenced both before and after culture.

More on evidence that SARS-CoV-2 has very much been isolated, analysed, visualized-up the wazoo!!
It's ignorance, stupidity, anti-intellectualism or nefariousness to loudly proclaim otherwise. If ignorance-ask us questions!
Not sugar-coating this anymore https://virologydownunder.com/sigh-yes-the-covid-virus-is-real/