Reading in the WSJ where CDC report on testing numbers was referenced. Mentioned that covid testing numbers had risen from 688 million (week of Dec 9) to something over 722 million the following week. With a population of about 330 million, how could those testing numbers occur. I am sure that I am missing something and several on this forum can explain! Not intending to create havoc, I just can't see how those numbers could be possible. Thanks for clarification in advance.

Those numbers don't seem possible. The logistics just can't be there for 700 million plus.

Those numbers are weekly totals as they were reported in the WSJ piece. Thus, everyone in US was tested at least twice or more in each of the weeks???? I get the demand rising ahead of holiday travel and festivities, but not at those numbers.

Those are cumulative. It doesn't mean they were doing 700 million tests that week.

Still, it's important that folks remember that with a false positive rate of even just 1%, 34,000,000 tests would result in 340,000+ false positives that week.

This is why it's bad policy to test people unless they're symptomatic or have solid reason to think they've been infected.

Good post.

I know two people that were tested this week and one was negative for rapid test but they also had them do pcr test. Second person was positive on rapid and they also had pcr done and sent to lab also. So I imagine those numbers are inflated because some places are doing rapid and pcr on same person at the same appointment.

Well, fortunately the false positive rate is around an order of magnitude lower than 1%, and the false negative rate is around an order of magnitude higher. So we got that going for us, which is nice.

Thanks, as I can believe those numbers are cumulative, but that is not how they were described. Possible the WSJ failed to properly describe.

Zobel said:

---

Well, fortunately the false positive rate is around an order of magnitude lower than 1%, and the false negative rate is around an order of magnitude higher. So we got that going for us, which is nice.

---

Do you have a source for saying the false positive rate of COVID-19 tests is around 0.1%? Because I've searched a number of times throughout the pandemic and the estimate has always been much closer to 1%.

Here's an interesting calculator on the BMJ: https://www.bmj.com/content/373/bmj.n1411/rr

Here is a peer reviewed study that estimated 95% CI is [0.01%, 0.12%]. Found via a quick Google search.


https://journals.asm.org/doi/10.1128/JCM.01080-21

Quote:

---

Overall, these very low false-positivity rates associated with high-throughput SARS-CoV-2 testing offer confidence in SARS-CoV-2 PCR test results and help laboratorians, epidemiologists, and regulators understand the specificity and positive predictive value associated with high-throughput NAAT.

---

PCR false positives are low.

https://journals.asm.org/doi/10.1128/JCM.01080-21

The antigen tests are much less reliable.

That's addressed in the BMJ article I posted.

Quote:

---

However, the situation is much worse than this because neither PCR nor antigen tests are close to a 99% specificity level in practice, for various reasons (Braunstein et al. 2021). Lee 2020 performed a lab analysis of the CDC PCR test accuracy, which was widely used in the first months of the pandemic, and found it had a 70% specificity (i.e. 30% false positives) and 80% sensitivity (20% false negatives). This is because of faulty designs built in to the test from the beginning, as various news accounts from the Washington Post, NPR and ProPublica have since revealed.

This level of inaccuracy matches the CDC's own internal report that found 33% false results when its PCR test was released in late February 2020...

---

So the PCR test may have a very low false positive rate if it's performed perfectly according to manufacturer instructions and with zero contamination, but in practice it's higher.

Here is the article that's cited there: https://europepmc.org/article/PMC/7934325

Here's another which is referenced in that article: https://www.medrxiv.org/content/10.1101/2020.04.26.20080911v4.full.pdf

Interestingly, it turns out that even at-home tests can (and ridiculously "should") be reported to health agencies as well and are counted in official figures, and I'm sure we can agree we should have a low level of confidence in those numbers: https://news.yahoo.com/home-tests-surge-doubts-rise-131854407.html

For the record, it looks like at-home tests are rarely reported and virtually never if they're negative, so it can't really factor in to the overall false positive rate of all the tests that are done at testing sites and reported.