im not arguing against the point youre making. all i meant to say is that there is excess death and thus kung flu cant have no impact at all

Well, technically, the answer to your question is probably "yes", but that's not relevant.

The testing used here is RRT-PCR. R means real time, RT means reverse transcriptase. PCR means polymerase chain reaction.

Reverse Transcriptase means that you use an ezyme to make a double stranded version of the RNA that you are looking at. For this discussion, we can ignore it - it just means that you are starting with RNA instead of DNA.

PCR is a standard DNA copying mechanism. Polymerase will copy DNA fragments that are presented to it with the appropriate markers attached. The markers are gene sequences with enzymes attached.

So, if you have a segment that you want to copy, you find unique portions on either side of what you want, and you create the complementary version, and you attach the appropriate enzymes to them.

You manufacture many copies of your markers, and put them in a solution along with polymerase. If you add to that solution some DNA, and if that DNA contains sections that complement that markers that you've created, those markers will attach, and the polymerase will run zip through the marked section making a copy.

Real Time means that there is a third part of the test, a Fluorescent dye. Fluorescent means that when it absorbs one wavelength of light, it will emit a different wavelength. So, at the end of each cycle, they illuminate the test wells with the excitation wavelength, and look carefully for the emission wavelength. Typically, we use a dye that gets less efficient when the molecule is bent by being closely coupled to a matching DNA strand.

So, our test solution contains: a start marker that binds to a specific gene sequence, an end marker that binds to a specific gene sequnce, a dye that binds to a specific gene sequence, and the helper chemicals (polymerase, reverse transcriptase, etc).

A real test will have several of these test mixtures, designed to match different sequences. What takes so much time after the virus genome seequnce is published is the search for suitable sequences. You have some tens of thousands of genes to look at, and you want to find about six sets of three sequences. You want them to be specific to this virus, meaning that they aren't found in other viruses or organisms, and you want them to be parts that haven't mutated as the virus is spreading.

Testing is done by preparing a plate. One of the most common plates has a grid of 8x12=96 wells and can be used to test 12 people. All of the wells in the first and last columns are prepared with positive and negative controls, and the middle six cells are prepared with (up to) 6 test solutions.

Then each patient's sample is applied to all of the wells in one row (except the negative control). The loaded plate is placed in a realtime PCR machine. The machine then heats the plate, and cools it, then it hits it with light and measures how much fluorescene is found in each well.

The positive control cell will replicate on every cycle and is used to confirm that PCR is happening. The negative control cell will replicate if there is any contamination and is used to suggest the proper procedures were followed by the lab technician - if it reacts, the plate should be thrown out and those tests should be re-run.

Since you can look for up to 6 sequences per test, you can make a few of them broader. So, you could have one column set up to basically detect some sequence common to the whole coronavirus family. In that case, someone with a cold would trigger that well, but not all of them. The overall test would be "ncov-19 negative", because the more-specific subtests didn't acivate. But it would technically be true that "some of the genetic material picked up by the PCR tests could have come from other related viruses".

There are some imperfections in these tests. It is common for some wells to activate a little bit. You normally plot the intensity of all of the wells by cycle count. The curves for the matching wells will be much, much faster than the curves for the spurious activations. Labs typically handle this by calling any curve that isn't exceedingly obvious a failure, which triggers a re-test.

But there also isn't a comprehensive catalogue of all gene sequences that might be out there, so it is possible for a test to inadvertantly be set up to trigger on something harmless. They try to make the tested sequences as long as possible in an attempt to reduce the odds of that happening.

After the sequence was published, labs around the world set about working on these tests. It takes time to dig through the genes looking for good fragments to test for, which is why it took a week or more for the first tests to start showing up.

This process is also imperfect. A lab may accidentally pick a sequence that isn't specific enough, or that is part of a region that mutates. They may also pick spots that for whatever reason it is difficult to manufacture the markers or dye for.

That last one, production problems, happened in the US. That's half of the reason why our tests lagged behind early on. The other half is because our regulatory structure had created a monoculture. There were about a half dozen other US labs that had working tests at the time, but none of them could be put into production because the FDA approval process was designed around one specific lab. And by random bad luck, that one lab picked a marker sequence that couldn't be reliably mass produced. (Eventually Trump had to step in and order the FDA to practively work with other labs to get their tests approved.)

Sorry if this is too long. I know it goes far beyond merely answering your question. Back when testing was a big topic, I spent a week learning about it in as much detail as I could, all the way through downloading lab manuals for some of the tests and then looking up the biology jargon used in them, and what the lab techniques looked like.

TL;DR - No, the common cold is not fooling our PCR tests.