Crunching the numbers

The one problem with being a scientist for many years is that you can take the scientist out of science but you can’t take science out of the scientist. It’s in their nature. When I left research science, I didn’t cease to be a scientist.

I still have a scientists instincts, motivations, thoughts and ideas. I cannot leave a piece of data alone without thinking of alternative analyses or different ways of looking at the same. Like all scientists, when I look at data I think “what if…”.

Like so many others I have watched this unfolding catastrophe with a kind of morbid fascination. The same fascination that prevents you from averting your gaze from a car crash. And the numbers emerging from the WHO and elsewhere (Johns Hopkins is a very good page) are fascinating in their insights into each national response to the pandemic. The data are, to use President Trump’s comically inappropriate adjective “beautiful”.

But you have to know how to think about the data. The raw numbers themselves are a code and it’s up to the scientists to decode the information. Let me give you an example.

Take the UK for instance (not that anybody would bother). 8000 cases of coronavirus more or less. 400 dead more or less. On the face of it that amounts to a 5% death rate for the condition. The number of dead divided by the number of cases. 5% is an awfully high figure even for this virus so can it be accurate? Other countries publish much lower kill rates. How can this be?

It comes down to testing. Covid-19 is not the only illness to present with a dry cough. Nor is it the only illness characterised by fever, aches and pains. And it wouldn’t be the first lung infection to mature into pneumonia. So a patient presenting with any or many of these symptoms could well have Covid-19. It’s a fair bet.

But it’s exactly that – a bet and not a certainty. The only way to be sure that it is Covid-19 is to test. Without the certainty of a test result, it is no more than a backed hunch. So it’s clear that you have to test in order to have a firm diagnosis, the correct treatment plan and the appropriate recording of outcome whether good or bad. Individuals need to be traced and tracked through the entire sequence of diagnosis to treatment to outcome.

In the UK, although things are changing rapidly, patients are mostly tested when they present in hospital. Many of these patients will be transferred to intensive care where their outcome will be documented. Not surprisingly, these are very sick people. Many die. So our testing programme in the UK is, until recently, focused on those who present as hospital and are therefore already very sick and thus more likely to die.

In order to get a true picture of the mortality of Covid 19, we need to know how many people in the country either have had the illness or currently have it in a very mild form. We have been told throughout that, say, 4 out of every 5 people who contract the illness will not find themselves hospitalised. We don’t have those numbers because, until recently, it was not part of the testing programme.

Yet these data are critical to our understanding of how the disease spreads and how ultimately it may be defeated. Without this information we are applying controls and measures of uncertain value. Why? Because we can’t assess their efficacy without a knowledge of the whole population. As it stands, all we have is this 5% mortality in the UK. If it turns out that four out of every five recover in their own homes, then we are in reality looking at a 1% rate. Much more plausible.

Don’t get me wrong – an illness which kills 1% of the country’s population, particularly the old and wise, is cataclysmic by any standard. A 5% kill rate on the other hand is apocalyptic.

We also need to be careful of comparing data over different time frames. The number of people diagnosed is straightforward and up-to-date. But the number of the dead does not have the same temporal consonance. Going back to the figures for a moment – 8000 diagnosed, 400 dead – we are looking at different time points. To put it bluntly, most people do not die immediately after being clerked. Patients may be treated for a week, two weeks perhaps, before they die. In this case, the 400 dead should not perhaps be compared with the current 8000 diagnosed but with the figure a week ago. Looking at the date of this way paints a more bleak picture. On this basis, the kill rate is much higher.

Let’s also factor in health service resources. The death rate obviously bears a relationship to the provision of ventilators and staff to operate them correctly. If the number of intensive care beds needed falls below those available, then patients are in with a good chance. If on the other hand the number of beds needed exceeds those available, the outcomes are inevitably going to be worse. In Italy, demand outstrips availability manyfold and doctors are having to triage the arrivals. Triage, most often applied in the battlefield context but then this is a battlefield, means dividing patients broadly speaking into three categories – those that will most likely survive without ventilating, those that will most likely occupy a ventilator and then die and finally those where there is a realistic chance of improving the outcome by treatment. Only the last category will have access to a ventilator. And the doctors in Italy have found themselves having to make those choices.

When the health service resources are inadequate, the death rate rises dramatically. And this is why when there’s been so much talk about “flattening the curve”. I have seen illustrations with graphs, memes and buckets of water. They all illustrate the principle well, that of keeping demand below supply by flattening out the number of cases per week. And on the face of it it looks reasonably optimistic until you factor in the harsh reality of numbers and acknowledged that even the best estimates put demand way above supply. Our health service already cannot cope and we haven’t even begun this battle yet.

Much is said where we are on the curve relative to Italy. Italy has become the tragic illustration of what happens when you don’t get it right. Complacency for perhaps two weeks when the condition wasn’t taken seriously as led to the present viral holocaust. In turn, other governments have learned or ignored the lessons of Italy. Only time will tell.

That is why social distancing, self isolation or whatever we want to call it needs to be taken seriously. Because this is where everyone of us can make a difference. If we become ill, we may need an intensive care bed. And if we are occupying it, somebody else isn’t. By becoming ill, we are in essence depriving another person of life-saving treatment. So when the Prime Minister talks about everybody doing their bit, this is what he means. We have to stay well so that others can stay alive. It’s that simple. For every one of us that stays out of hospital, somebody who needs to will be able to. This is what flattening the curve is all about. Because if we don’t, the alternative is unthinkable.