PCR Ct values and Infectiousness correlations

2 min read


This study examines samples from the England epidemic peak (Spring) to assess correlations between PCR Ct values and infectiousness 👇🏼

The link to the full Eurosuveillance paper is within the comment below, dated Aug-2020.

🧪 Yes, it’s the same world-renowned publication (owned by ECDC) that put out the first PCR instructions that informed the design of PCR tests globally.

⚠️ And yes, there is an ongoing ‘scandal’ surrounding that paper, referred as the Corman-Drosten Report. In November it was formally challenged for various significant scientific errors within, and they have yet to release an official response  – over nine weeks and counting! They had suggested this would be done by end of January. More details on this can be found in the comment below.

That aside, the paper mentioned below is interesting.

🤏🏼 Of course, we must caveat this finding with the fact the samples were taken during the actual epidemic outbreak – i.e. in spring. The virus and disease dynamics back then are observably different now due to developing herd immunity and virus mutations etc.

👀 The key observations are cited in the graphic.

🔹PCR error rate, correlations between Ct and viable virus, and infectiousness durability are all interesting findings.

🔹There is also an observation within this Spring dataset that less than half of those PCR positives went on to develop symptoms where they could culture SARS CoV2.

🔹The majority of the asymptomatic PCR positives were in the 80+ category, but the reasons for this were unknown. The speculate on sample bias and/or reporting/recall issues.

Ct Values vs Infectiousness

Time to rethink mass PCR Testing?

Net-net, this builds on the strong case to apply much greater scrutiny to the usefulness of PCR testing as a community testing tool outside of the epidemic period (i.e. post Mat 2020).

🤔 Combine this with the gene knockouts we have seen due to mutations and variants, the lowering community prevalence as we draw to the end of winter, and WHO’s acknowledgement to retest weak positives… and the case of PCR Community testing is fading quickly.

🏥 PCR Testing has utility within a hospital setting, where expert labs are leveraged to assess aetiology of severe COVID-suspected patients – be it community acquired or hospital acquired infection.

❌ But as a proactive screening and surveillance tool that directly effects public policy…. not so much.

P.S. ONS have released a huge Infection Survey report where they break down many details, including what they have seen in regards to Ct values and positivity rates PER TESTABLE GENE. Once I have time, I’ll work through this and will provide some of the highlights.




Eurosuveillance paper listed below, including the Corman-Drosten Report Challenge piece.


The Original Facebook Post

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One thought on “PCR Ct values and Infectiousness correlations

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  1. Hi Steve Katasi, thank you very much for this, it very much confirms the impressions that I have formed that this virus has a very short life-cycle!, this also appears in the current sudden changes in the reported infections and deaths in the UK!, it is now very clear that most of the people that become infected, then ill and then die do so within a very short period!, roughly between seven to fourteen days of symptom onset.
    This would fit very nicely with the concept that the disease progresses very rapidly and if the immune system does not kick in and overcome the virus the patient dies quite quickly. There is of course a lot of attention devoted to the small number of long term sufferers but it would seem that most of them are suffering from the side-effects of the infection and their other problems!, the virus is no longer involved and they are not infectious!.
    While this body of evidence is still building it is not possible to come to any definite conclusions other than the probable timeline for transmission and illness excludes any chance that the lockdown measures have had a significant impact on infections!and the PCR testing has been no real help!. Cheers, Richard.

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