Most US labs still declare a positive result if viral matter is detected at up to 40 cycles, which is 32x the "magnification" of 35 cycles.

All test results should include the PCR cycle count at which the viral matter was detected.

This is so crazy. So the plan was just keep replicating until you get the answer you want?

if you think it's the plague, you want the diagnostic test to be very sensitive

but it's not the plague, at least not for people under 70

or worse, as a screening tool in healthy people.

Exactly.

The test itself is fine. The PCR machine does exactly what we ask of it.

But the policy around the tests, including deciding who to test and assessing the results and making decisions from those assessments, needs re-evaluation.

We're not going to be able to test our way to zero COVID.

DadHammer said:

---

This is so crazy. So the plan was just keep replicating until you get the answer you want?

---

No one is doing this. Manufacturers of the PCR assay do studies on various viruses and bacteria and come up with a general number of cycles to use if you're testing for different things.

Maybe when you test a urine sample you only need 20 samples to detect gonorrhea, but you need 35 cycles to detect chlamydia. Since both tests are typically run simultaneously, you'd probably go with 35 cycles. Does that mean that the extra cycles are detecting clinically insignificant gonorrhea?

Likewise, maybe you need 40 cycles to detect the influenza virus, or RSV. When this was inundating Italy and New York, there was no time to run PCR samples for different cycles and then determine which samples also produce viable virus. I'm sure some manufacturers just turned it up to 11 while others probably used numbers similar to other assays that detect RSV, or flu, or other respiratory viruses.

Also, I don't think this is study necessarily means what it's suggested to mean. We know that infected cells will continue to produce viral RNA even after clearing the virus. And we know that detectability varies depending on where in the infection cycle you are. A positive test with someone on the upslope of infection is very different than a positive test from someone on the downslope, regardless of the Ct used to detect it.

But I do agree that we need to understand the data we're producing before we make policy decision off of it. And we need to be willing to change what we believe as the science develops. A lot of people are saying we shouldn't be testing asymptomatic people, but you know what, Americans love to get tested for stuff, especially when insurance or the government is paying for it. Even if it won't change management, they want testing. And as long as they want it, and someone will pay for it, then the free market will provide it.

But, let's also keep in mind that asymptomatic testing isn't without merit. When Marines went to Okinawa a few months ago, they all quarantined for 2 weeks prior to being released to their regular housing. During those 2 weeks COVID spread throughout, with largely asymptomatic infections, until it stopped being asymptomatic. Over 100 cases in military members, likely contributing to the 2000+ cases in local nationals, and 40ish deaths. On an island with one of the oldest populations in the world, this is kind of a big deal.

sorry to don't say what you want to hear