A Journal of the Plague Year (4)


Image Credit: Imperial College, London (my old school!)

March 20th, 2020

As I write, Italy seems to be approaching a moment of truth. The case load for hospitals in the Lombardy region appears to be near critical. MIT Technology Review is running a website “Radio Corona” with excellent interviews with some of the leading medical minds—check it out.

I want to address a few points here that fellow scribes have raised which I think display faulty reasoning. And there is confusion about the absolute numbers, relative numbers, and the rate of change of numbers, each of which have different importance.

Point 1.

Much is made of the numbers of cases and deaths due to Covid-19 as compared to the standard flu that occurs every year. As Dalwhinnie points out (quoting the illustrious Professor Briggs):

• In Wuhan itself, the City of Doom, some 2,446 souls departed their fleshly existence earlier than expected. Google tells us the city has between 11 and 19 million, depending on whether you count the entire metro area as “the city”.
• The city had 49,995 cases. The case rate was 0.26% to 0.45%, depending on what China called “the city”. The total dead rate was 0.01% to 0.02%. The case dead rate was 4.9%.
• People fixate on that last number, forgetting you first have to get the bug before you can die from it. But everybody now seems to believe they’ll get it with certainty. Review Bayes Theorem & Coronavirus!

Nothing is wrong with these numbers or with the application of Bayes’ Theorem to the problem. However, it’s right only so far as it goes. The city had a total case rate of nearly 50,000 (0.5%) which doesn’t sound that bad, given a population of nearly 15 million. But this is only weeks AFTER a total shutdown of the city was instituted when even the Chinese leadership realized something big was happening. This is not what would have happened had that action not been taken. Witness Italy now and figure how far they were (are) behind the Chinese curve.

Further, this massive case load was IN ADDITION to the normal hospital case load of any city anywhere. And thousands of doctors and nurses do not miraculously appear overnight to care for them.

Moreover, it was only after the lockdown that (more than a week I think) the rate of increase of cases began to fall off. The effects of pushing down the value of R-naught, the base reproduction number, to below one led to this. Case numbers continued to rise due to the appearance of symptoms in those who were already infected prior to the lockdown.

Point 2.

Even if a health care system can cope with greatly increased numbers at various times, a tsunami of new cases can rapidly overwhelm even the best system. Despite the fact that the Chinese government was criminally negligent at the beginning, at some point something snapped in the leadership when they realized that this thing will not go away or be suppressed politically. It was then that mass action started. Europe, and especially Italy, did not follow this path and is paying the price.  (CIDRAP, the Center for Infectious Disease Research and Policy, at the University of Minnesota is an excellent source).

It is not only hospitals and the medical workers that are affected, all kinds of supply chains and manufacturing are affected, especially in the West. Or they will be. As I alluded to in my previous missive, it’s not the absolute numbers at any time that count, but the rate of increase and the transmissibility of the thing.

Point 3.

Testing— Of vital importance, not only for those who are becoming sick, but for the general population currently unaffected, but possibly infected. This latter group is the source of further spreading. Tracking contacts and quarantine is the way to stop that and South Korea has shown that this works.

When an antibody test is available (apparently quite soon, maybe in a few days), this will enable us to detect persons who have been exposed to the virus and developed antibodies but have never become sick. Knowing this can give us a much better idea of the number of people who have been infected but never displayed sickness and the number who become sick (the afflicted). This greatly affects assessment of the case fatality rate.

If the health care system becomes overwhelmed at any time, the case fatality rate will rise as many sick people will get no treatment at all. Check out the graph at the top for possible scenarios.

So that’s it for today. This will not go away in a few weeks, we’re all in for a bumpy ride.

Rebel Yell