Keep on Keeping On - Day 24

The outbreak of SARS-CoV-2 (the coronavirus) continues. It's a pandemic, which means, of course, that it now is just about everywhere.

As I've said a few times now, I am an epidemiologist, which means that my work focuses on public health. I've spent most of my professional life creating and abstracting information from models.

The president last week warned Americans that the coming days were going to be very difficult, and that admonition has not been wrong.

The news, while terrible, is not completely bleak.

I am following a number of analytical sources each day, trying my best to understand the evolution of the crisis. Two in particular are, I find useful.

The first - the COVID Tracking Project - is provided by a group of journalists, initially led by Robinson Meyer and Alexis Madrigal at The Atlantic. It tracks state-by-state reported statistics on total tests done, how many are positive, how many are negative, how many tests remain to be resolved (results confirmed and reported), how many patients are hospitalized, and how many people have died.

The former are critical from an epidemiology perspective, as we get a feel for the cumulative impact, and importantly, the day over day change. We hear a lot about "bending the curve." For this, the rate of change is a key metric; at least as much as the cumulative impact. The cumulative impact details the past - something we cannot change. The rate of change is more immediate, and can be impacted by choices that we make today.

The latter is important because tracking hospitalization gives us a much deeper view into how the disease is actually manifesting. As is now well-known, about half or so of people who get infected are either totally without symptoms, or have mild to moderate symptoms. They don't require hospital, and overwhelmingly will recover. For these people, COVID-19 will be an unpleasant experience. It won't be a fatal one. The more severe cases - ones that require hospitalization, or worse, ICU admission - are the ones that really drive the magnitude of the fear. These are virtually all of the patients who will die. They are the ones who will compete for resources.

I recommend to bookmark and check their data each day.

The second is a project run by the Institute for Health Metrics and Evaluation (IHME), a research centre at the University of Washington in Seattle. As an aside, I know, personally, more than one person at the University of Washington Department of Biostatistics, and it is one of the best in the world.

This team uses reported data on infections, mortality (death), hospital admissions, ICU admission, and ventilator demand to model the trajectory of disease. Data at one point were updated nearly daily. Updates now are regular, but not quite at the level.

This is one of the models the US government looks at when making decisions on resource planning, and it is the one that Dr Deborah Birx often refers to in the daily press briefings.

Like the COVIDtracking group, the IHME estimate, on a state by state basis, current predicted hospital loads and mortality. But they go a level deeper - projections are made on admissions to ICU and itubations (need for mechanical ventilation). The latter two are critical to understand the ability for our health care systems to meet life-saving demands of the infected population.

Predictions on mortality are also offered.

You can go to the site and see how your state is "doing" with respect to mortality and demand vs. resource needs.

Initially, the model predicted that mortality in the US would grow, slowly at first, then rapidly (a classic exponential growth model) until mid to late April, plateauing, and then falling until about June. When the statistical dust settled, it forecast around 100,000 deaths in the country, with a range of 75,000 to 250,000.

Those are terrible numbers.

About 95% of the country is now under direction to observe "social distancing" - an awkward phrase that really just means "separate yourself, physically, by about six feet from other people." It means to stay home unless essential - going to the grocery store, for example. And it means being vigilant about hand washing.

The results are starting to come in.

Friday, the predicted mortality of the US from this forecast model was about 95,000.

Monday, when updates were available, that number had fallen to 81,000.

The latest news this morning puts the estimated number at just over 60,000.

That's a lot of people. But it's a third less than the initial estimates.

Actions taken by people are starting to show results. The mortality curve is flattening. Here is how it looks as of today:

The coloured range should get your attention - this is a band of uncertainty (remember; these are mathematical models). The current situation has a range of about 40,000 to as much as 130,000 dead. The total mortality could turn out to be 130,000, even given where we are now.

These are, it's worth noting, models. As Dr Fauci noted, models have utility, but data are better. Statistician George Box famously quipped that all models are wrong, but some are useful. For me, this model is quite useful.

You'll also note that the line is solid until today - this is the historical data. The dotted line are projections. If that solid line trends back up, projected mortality is going to go up even more.

I re-iterate the point I've made a dozen times.

HOW this plays out is up to you. It's your choice. It's your future.

The final narrative is ours - whether it's a scary and terrible chapter, or a catastrophe.

These data are a hopeful sign. But they also should be a warning.

Stay home.