It is now painfully and woefully apparent the US is ensnared in a massive and rapid pandemic spread of Covid-19 infections. All 50 states are now officially affected, as West Virginia finally found and confirmed its first case.
As of this morning, the State Health Department website indicated that 80 tests had been conducted and none were positive. Other infections are already there and silently lurking. President Trump has done another disservice to all Americans with his casual and stupidly wrong statement earlier today that West Virginia was virus free and the Governor had kept it out, literally a couple of hours before the veil came down. As if.
As the toll of reported cases mounts frightfully quickly, one of the critical estimators of the speed and ultimate burden of disease is the epidemiological doubling time.
In simple terms: how long does it take for the total number of reported cases to double in number. At the beginning, the educated expert guess from experience in other countries was about 7 days. Early US numbers since March 1 have suggested this was too low an estimate, thus understating the speed at which the Wave is washing over America.
For the last two weeks the actual doubling time has been about 3 days, rather consistently.
Here is a simple tabular tool, a Mental Abacus if you will, so that for any given starting time, you can do a simple point and count to arrive at an approximate doubling time without an electronic calculator or fancy mathematics, useful as they are.
The data are derived from daily 9 PM snapshots from the magnificent John Hopkins Covid-19 Tracker, which everyone should consult.
Here is today’s updated Corona Mental Abacus Tracker. The data for today was taken from the 5 PM snapshot.
To find the approximate epidemic doubling time in the US, here’s what to do.
Find a cell such as Monday March 2. The cases reported were 102. Next move to the right to find the first cell with a cases reported number at least 2 times that in the first cell. In this case that would be Thursday March 5 with 233 cases. Then count the number of days after the first cell to the double cell. In this case it is 3 days later. The doubling time from March 1 was 3 days.
One more example to explain the procedure. Let’s find the US case doubling time after last Saturday March 14. The cell entry is 2,796 as shown in the Mental Abacus chart.
There is one trick. When you count cells to the RIGHT and reach the end of a week, go immediately to the next week UP and continue the count from the LEFTMOST entry. To continue this example, double 2,800 is 5,600 so the double cell is Tuesday March 17. So, the day count is also 3 days. The doubling time for US reported cases as of March14 is 3 days.
Actually, since the reported case number for this Tuesday is 5,894 which is about 5% more than double Saturday’s number, the actual case doubling time is just a bit less than 3 days. But for a visual inspection tool using elementary math and no fancy models or computer simulations, this estimate is both practical and accurate for public policy and communications work.
To further illustrate, take the doubling time from March 1. The reported cases were 87. Double that number is 180. Moving to the right along that week, the double cell is Thursday March 4 (233 cases). But 233 is really somewhat more than needed. However, the previous day’s total for Wednesday March 3 is too low at 158. So, the actual estimated doubling time is somewhere between 3-4 days.
With an index finger and some grade school math, you can track the US Covid-19 doubling time for all practical purposes.
There are very smart people with very fancy computer setups and detailed models that are essential for many critical public health purposes as we go forward. Like projecting how many hospital beds we will be short, and how many ventilators we will need that we don’t have today. They need to work harder and keep at it.
But these folks can never deliver their precise estimates each and every day without distracting from their jobs and their life saving mission.
What the rest of us don’t need right now is more excuses and delays from politicians or others fuzzing up the clear trends by claiming “no one knows” or “it’s too hard to figure out”, or “the best people tell me”. Here is the People’s Abacus. You can figure out how the epidemic is doubling daily in near real time for yourself.
And by extension whether the current social distancing and restrictions are helping a little, a bunch, or not much as the days go by.
Sort of a personal fact checker against Covid-19 Happy Talk
A sustained doubling time of 3 days without substantial reduction in the near term (next few weeks) should frighten the Bejeesus out of everyone. A doubling time of 3 days means that reported cases will quadruple every week. That is twice as bad a rate of spread as the early model estimates were using. Every doubling of US cases will take a worsening toll of illness, misery, and death among our fellow citizens.
We shall see together.
Protect Yourself
Be Responsible for the Sake of Those You Love and Others Too
Mitigate, Social Distance, and Shelter For 8 Weeks At Least
