“Pump and circumstance” in the days of Coronavirus
If you walk along Broadwick Street in London (UK), will pass a lovely traditional British pub on the corner with Lexington Street. The pub is not called the ‘King’s Arms’ or the ‘Black Bull’ or one of the many iconic pub names. It is called the ‘John Snow’ pub. That’s unusual. Even Charles Dickens doesn’t have a pub named after him in London (although we know the pubs that he frequented). So, who was John Snow and why the pub name?
If you stand outside the pub, there is a red plaque on the kerb and a shiny, black, hand-cranked water pump nearby. This water pump marks the creation of one of the most powerful tools in medicine: epidemiology. Epidemiology is a branch of quantitative medical science that deals with the incidence, distribution, and control of disease in a population. Its underlying hypothesis is that you can understand disease and how to tackle it using only mathematical predictions. John Snow was the doctor who proved that you could do this. It has remarkable parallels to our coronavirus pandemic and Snow described all this in 1854 in relation to an outbreak of cholera.
Snow, against all common wisdom, postulated that a transmissible factor (we now know it was a bacterium: Vibrio cholerae) was being passed through the population. When he mapped the geography of the outbreak, he was able to identify the epicentre from which cholera was radiating. When he went to this ‘bullseye’, he found a common water pump used by the local residents. He speculated that this was the source of the cholera outbreak and the disease was spreading in a circle from the pump. His solution, admittedly experimental, was to remove the handle of the pump temporarily. Soon thereafter, the cholera epidemic subsided. Although only a small enclave of London was involved, over 600 people died of cholera, before it was brought under control.
A beautiful side-story to this was that workers at the local brewery never developed cholera. This was probably because they drank beer, which is boiled with hops and would have killed the bacteria. Also hops contain natural antibiotics. These were fortunate outliers to his geospatial model of infection. Nevertheless, Snow was able to confirm his hypothesis about disease transmission through water. This occurred seven years before Louis Pasteur proposed the germ theory of disease transmission. Snow achieved his ground-breaking discovery using conceptual mathematical principles, but the practical outcome was undeniable. Find the source, block transmission physically and count the numbers afflicted, which went down dramatically.
As I write, the Johns Hopkins website reports a total of 439,000 people confirmed infected with 19,700 deaths due to Coronavirus complications. This looks like a very scary statistic (~4.5% risk of death). It is much less than this in practice, because there are probably millions of unconfirmed/untested occurrences. Imperial College, London estimates that the risk of death is 0.5%-1% of actual infections. These odds are much better, but still pretty sobering. The Draconian measures taken by most responsible governments are essential if we are to turn the curve from exponential growth to exponential decay. There is evidence that we can do this coming from China, S.Korea and possibly from Peru. Most countries are still showing exponential increases. The countries that stick to the protocols resolutely will see improvements in the next 2-3 weeks. We won’t be out of the woods by any means, but stabilization allows us to act cautiously and rationally, if our leaders are following sound science and acting on epidemiological models. Predictive mathematics are just as important as healthy behaviour right now. They have proven to be remarkably accurate overall.
Viruses aren’t clever. They are just biological machines that have one "objective": to reproduce themselves. Humans are clever. We are capable of doing an end-run on the inexorable reproductive cycle of a virus.
The principles here are not very much distant from Snow’s original idea. True it is a virus, not a bacterium. Secondly, you don’t have to go to the pump (or in this case the Wuhan live animal market) to get the disease. It is passed on person-to-person. However, mathematically this can be incorporated into Snow’s original methodology. Isolating the pump is virtually the same as isolating the person. It isn’t forever, it’s a temporary measure, but if it is done cleanly and with fastidious detail, it will work. There is nowhere for the virus to go.
Today, we are all potentially a Broadwick Street pump. We don’t know for sure who is a ‘pump’ and who isn’t, but we all know what we have to do. Turn off the possible pumps for sufficient time for this to work. It will work. It is working and we now see a trickle of positive results. The academic mathematical models are believable and reliable. They predict short-term pain for long-term gain.
Once we have vanquished this, we will all be able to meet down the pub again and drink to John Snow and his academic progeny. For now, let’s remember that Snow had to endure hundreds of naysayers who disbelieved him, including important civic figures. We have the same, but we must insist that we all, including our friends and neighbours, adapt to this very tough period. For us, it is really no more onerous than it was for East Londoners in 1854, who had to walk many blocks for alternative sources of water. There is nothing new under the sun (Ecclesiastes 1:9).
When it is all over, you may hug a mathematician, preferably in the pub.