Fallacies and Fatality Rates

Politicians and the media have become our public health advisors and experts in 2020. This has been incredibly painful to watch. So much so that I have not looked at a newspaper or turned on the television in months. Public health appears to have folded to pressure from ill informed sources instead of following existing evidence. Pandemic plans were in place. Mass panic and collective pressure saw them abandoned with few exceptions as ill conceived experimental ideas such as strict curfews, mask mandates, cancelling all travel, closing borders and closing most businesses for indefinite periods replaced evidence based practice. The consequences are most severe in the world’s poorest communities and lives have not been saved, but expended.

Covid has taught me many things. Oneday not long ago I listened as a young and very enthusiastic doctor informed our team of the case fatality rate of Covid-19, claiming with an air of excitement that it was somewhere between 4% and 13%. Disturbed by such blatant fallacy I raised my hand and said US CDC have only recently estimated the infection fatality rate to be around 0.65%? She dismissed me with “that is definitely wrong” before continuing her presentation. It felt like a staged display of medical technocracy, with no questions or challenges tolerated.

It was also a clear example of the phenomenon known in science as “extension neglect”, where the size of the sample is ignored. With most cases of Covid having no or few symptoms, the number of infected people is many more than those who present for testing, particularly in places with high infection rates. The total number of infected people is the true denominator where you divide the number who died by the total number infected, for a fatality rate. Calculating a fatality rate using only those tested in a disease like this ignores the true denominator, ensuring a falsely high rate. This is unavoidable at the beginning of a new epidemic. For example, if you know of only two cases and one of them has died, your case fatality rate is 50%. When you learn of a third case who survives, this rate drops to 33.3%. This leads to the well known phenomenon of fatality rate reduction as an epidemic progresses. As the number of unknown cases (infections without symptoms) grows, the fatality rate also decreases and it becomes incorrect to only include those tested for a disease as your denominator. This is a complicated mathematical process but the picture below demonstrates it in a basic way.

The official fatality rates being headlined in Australia seem to be based on this fallacy of extension neglect. Without any discussion of the complexities relating to fatality rates, using crude numbers gives a falsely high impression of how dangerous a disease seems to be.

Another concern is the issue of the testing itself. PCR testing looks for pieces of viral RNA (genetic material). This can be RNA detected within the cell of viable virus as per this picture.

However it can also be remnants of RNA lingering after viral destruction, meaning that the infection may have resolved but the test remains positive. PCR positive results can linger for many weeks after an infection has resolved, meaning that having a PCR positive test does not automatically mean that the tested person is infectious. Mike Hearn discusses the problems associated with PCR testing in two recent blogs: Pseudo-epidemics and Pseudo-epidemics Part II. I also enjoyed his challenge to Epidemiology practices as they have played out in 2020: Is Epidemiology Useful?

Added to the imperfections of PCR testing is the issue of repeat testing. The disease reporting system must have a way of ensuring that multiple positive results from one person are not counted repeatedly in the case numbers as they represent a single case, regardless of how many positive test results they may receive. Criticisms of reporting systems in places like Spain suggest that many tests from a single case are being counted as multiple cases. I suspect this is unlikely to occur in Australia where we have an established, robust disease surveillance reporting system in place.

The following thread in Twitter this morning makes an easy, comprehensive read worth sharing. Attributed to Abir Ballan.

1. In March, WHO said: 80% of infections are mild or asymptomatic… (not more dangerous than other respiratory viruses).. This was concluded from the cases they were seeing in primary care and hospitals. Many more cases never reach the hospital because they are too mild.

2.Cases of a respiratory infectious disease are always a small percentage of real infections. To calculate total illness of the flu, they use a multiplier of hospitalizations https://www.cdc.gov/flu/about/burden/how-cdc-estimates.htm

3.C19 is the 7th coronavirus and cross-immunity is a known scientific fact. Why did the world speculate otherwise for this virus, I don’t know.

4.Since not everyone in the world will get it (pre-existing immunity), taking a phone and punching in the CFR of 3.4% by the world population was the craziest thing I saw.

5.CFR is never a good measure of the lethality of a disease. It declines as the epidemic progresses and the denominator gets larger. It was used to scare people who don’t know this.

6.Dr Fauci -believe it or not- said “ the overall clinical consequences of Covid-19 may ultimately be more akin to those of a severe seasonal influenza (which has a case fatality rate of approximately 0.1%)” on March 26, 2020. https://www.nejm.org/doi/full/10.1056/NEJMe2002387

7.Dr Bhattacharya estimated the IFR @ 0.17% end of April. No body stopped and changed direction. https://www.medrxiv.org/content/10.1101/2020.04.14.20062463v2.full.pdf

8.Viruses don’t disappear until there are no susceptibles= herd immunity. It’s a scientific fact.

9.Locking down whole cities was the craziest thing to do even back in March, with the little information we had, we knew enough.

10. Damaging the economy has serious consequences among them lost lives and livelihoods, mental illness and weakened healthcare systems. How did governments allow themselves to overlook this???!!

11.Small strategies could’ve been implemented to reduce spread: protect those at risk -only- as much as possible, work from home if u can, distant learning for university students, skip closed crowded places (nightclubs and pubs), skip crowded events (concerts),…don’t shake hands, wash hands, stay home when sick,. This applies to when the pandemic was here, not now. When you use small strategies you can add and subtract as needed.

12. We don’t have a vaccine for any other coronavirus so it’s better not to count on an imaginary silver bullet. Hopefully, we’ll get a safe and effective one that has been tested diligently to be suitable for the population at-risk and not for the healthy and young.

Vaccinating those not at serious risk is called overmedicalization. The risk of the a vaccine (as in any other medication) is higher than the benefit of not getting C19.

Anybody with a public health background who didn’t speak up back in March is too risk averse.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s