COVID-19: No There Isn’t A PCR ‘Casedemic’
by Raywat Deonandan, PhD
Epidemiologist & Associate Professor
University of Ottawa
(I add my credentials to these COVID-19 blog posts in case they get shared. I want readers to know that my opinion is supposedly an educated and informed one)
So, there is a prevalent claim that the COVID-19 cases being logged all across the world are horrendously overestimated, due to the hypersensitivity of the PCR test. Essentially, they state that what we are seeing is a “casedemic” and that there is no “second wave” and no pandemic at all.
I am not going to link to, or name, any of the prominent people making this claim. I don’t want to give them the exposure. But you can do your own Googling.
This is a topic I was hoping not to wade into. It’s guaranteed to elicit more hate mail from the predictable corners of the Trollverse. Or worse, it will elicit a flood of messages asking me to respond to various YouTube videos claiming various quasi-scientific things. I’m much too tired to deal with any of that.
More to the point, today’s topic is one that is outside my specific expertise. I’m a population Epidemiologist, not a PCR user. While I have training in laboratory sciences, I would never claim expertise in microbiology, virology, immunology or any of the disciplines of the lab and test tube.
So to address this issue, I have sought input from true experts, some of whom have asked to remain anonymous. And I have found excellent and informed sources written by authors that I trust. I have attempted to summarize their responses in language accessible to the layperson.
The “casedemic” argument typically involves a thing called “cycle threshold“, or Ct, which imprecisely is the number of times the PCR test was amplified before a viral signal was detected. The higher the number, the more marginal or fragmentary the virus being detected.
There is disagreement in some circles about what the appropriate cut-off should be: 25 cycles? 30? 35? Anything more, they claim, and we have “false positives.”
As a result, many are claiming that the epidemic curves we are seeing, and that the media is reporting, are artefactual, the result of the improper use of a technology that was not meant to be a surveillance tool.
Response #1 – This is partly semantics
One microbiology expert exclaimed to me, “what people are actually arguing about is, ‘what is the definition of a case’?” She felt it was a pointless discussion.
What she meant was that a PCR test is very sensitive. It can detect viral presence well before symptoms arise. And it can detect the remnants of viral presence well after symptoms diminish. So what do we care about? Do we only care about the individual while he is in the throes of symptomaticity? (Is that a word?) Or do we care about him at all times?
If the PCR test detects you before you are infectious, well that’s great. You’ll be an infectious case in a day or so, so it’s good that we know about you. And if you’re no longer infectious, well you likely were at one point, so you’re still a case… just from some days earlier. The case status is still real.
In either interpretation, the case is/was real. The controversy is in when it should be coded. And really, that only applies to a handful of instances.
Response #2 – There is nothing magical about a Ct cut-off
As noted, I am not an expert in PCR technology. But Australia’s Dr Ian Mackay is. He has written a scathing takedown of the casedemic argument called, “The “false-positive PCR” problem is not a problem.”
Summarizing Dr Mackay’s argument: A Ct cutoff of a particular number is not important. What’s important is the overall assessment of the case, since there is biological variability. He adds, “To say that any PCR run for more than thirty-something cycle will be a false positive, or increase the likelihood of a false positive, is misleading and wrong.”
He also presents strong evidence that high Ct PCR tests very often indicate infectious persons. So it is foolish to dismiss high-Ct results as you will inevitably undercount genuinely infectious cases.
Response #3 – Lab people aren’t idiots
COVID-19 is the most studied viral disease of modern times, perhaps in all of history. All the labs of the world, all the lab experts of the world, are focused on its detection. Conferences are held regularly to discuss these very issues: how to calibrate Ct levels, how to define cases, how to avoid false positives. It’s the height of arrogance to assume the risk of high-Ct oversensitivity would not have been considered.
Here in Ontario, our public health labs conduct regular audits on the propensity for PCR tests to detect false positives. As you can see from table 1B of their September audit, a test of high Ct tests against secondary gene targets revealed that while false positives do occur, they are very rare.
They are even rarer when there is a high pre-test probability of infection. That means if the person is symptomatic, the probability of a false positive diminishes greatly. And right now, we are almost exclusively testing symptomatic people.
Response #4 – Australia, New Zealand, Singapore…. duh
You don’t need to understand PCR technology or biostatistics or any fancy science to get this point. Countries where COVID has been mostly eliminated still test at scale using the same technologies and criteria that we do, and yet…. nada. No positives found, false or otherwise.
New Zealand conducted over 37,000 tests this past week. and yet detect fewer than 10 cases. If we assume, as would the casedemic people, that they are all false positives, then that’s a false positive rate of 0.03%.
Now apply that statistic to Ontario. We conducted 56,000 tests yesterday. And yet 3.6% of those came back positive –not 0.03%.
In other words, if the PCR test were detecting all these false positives, where are they in Australia and New Zealand? Those countries conduct very large numbers of PCR tests daily, including high Ct instances, and yet no “casedemic” there. That’s….odd. No?
Response #5 – The world is in crisis
Claiming that there is a “casedemic’, that the pandemic is nonexistent, is a good example of the old joke, “Who you gonna believe? Me or your lying eyes?”
In many parts of the world, COVID wards are over spilling. Utah is unofficially rationing care. Alberta is asking for military-style field hospitals to be built to deal with their explosion of critical cases. And in the USA, COVID-19 is now the single biggest killer, exceeding that age-old champion of lethality, heart disease.
For all of that to be true, and for their to be a fake “casedemic”, a lot more delusion needs to happen. But at this point of my science communication efforts, I fully expect to hear accusations of faked data and fraudulent video.
To quote every teenage girl on American dramatic TV, I just can’t even anymore.
The “casedemic” narrative is nonsense. As noted, I’m largely out of my expertise depth here. But you can read smarter people than me on this topic.
In addition to Dr Ian Mackay, I recommend “There Is No ‘Casedemic’” by Gideon M-K, and “There is no COVID-19 ‘casedemic.’ The pandemic is real and deadly” by David Gorski.
Hang in there, people. We can get through this together.