This is a simple posting about what the doubling time of a virus means for our future expectations.
We can expect a 3 week or so doubling of cases of Ebola until such time as we gain control of the spread or develop an effective cure. That may take a while. So what happens until that point? How much worry and how much time?
So lets just list a set of “doubles” and realize that it is about 3 weeks between each set. We had our first (not flown in by a medical air ambulance) patient in Dallas. Now a couple of weeks later, our first home grown transmission (to his nurse, despite medical protective gear). So that is our first “double”, from 1 to 2.
2 4 8 16 32 64 128 256 512 1K (that '1k' is about 1000)
In weeks, that’s roughly 3 x 9 or 27. Call it about 1/2 a year. Just a while ago, Africa hit the 1000 patient mark, so we ought to expect that this all started about 1/2 a year ago. (Someone can test that if they like by looking up the index case and seeing how good the fit might be.) Now what happened after that 1000? Doubling continued. That same row can be repeated as 1000’s if desired.
2 4 8 16 32 64 128 256 512 1000x1000 (or One Million).
Now last news I heard had Africa at 4000 dead (and about 8000 infected). That puts them at about 3 x 12 weeks, or about 9 months into it. That is where we ought to be about next July… But where will THEY be by then? A whole lot worse. Now we can repeat that doubling as millions.
2 4 8 16 32 64 128 256 512 1000 Million (that Americans call Billions, and Brits don’t ;-)
OK, so the world ought to be about 12 steps on by then (next July). Counting from 8k now, we get about 32 Million. Doubling Time is a bitch…
For the USA, how long to that 256 (that is nearly the entire population)? As we are already at 2, counting forward is 9 to the end of the first line, then 10 on the next line, then another 8 on the last line. 27 x 3 weeks, or about 81 weeks. Call it 20 months, give or take, until everyone in the country is either exposed, sick, or dead. That is ALL the time you have to find ways to stop the transmission. One year, 8 months. With a wall around the country and no new imports.
Now the world as a whole is already at 8,000 so how long to, oh, 8 Billion? It is a 17 count to 1 Billion, then you repeat the line of doublings as Billions, and get another 3, So 20 x 3 weeks or 60 weeks. Call it about 15 months. One and 1/4 years. Tops.
Do I think that will happen? No.
Long before then folks will start stopping this disease. If not by modern medicine, by good old fashioned quarantines (that were used since they worked… without modern medicine). At some point air travel shuts down and lots of folks shelter in place and figure they will deal with the side effects of not going to work after they find out who is still alive….
But this exercise DOES put an upper bound on how long this can go without a fix. February of 2016, we run out of world to infect. This event will be measured in months, not years. That is the tyrany of doubling time. (Or exponential growth).
Again, though, I have to point out that before that actualy happens, the S curve nature of real growth will bite. We will run out of pilots willing to fly to infected places. We will run out of folks willing to congregate in airports (or factories, or…) and things will stop; even without a cure, fix, or change of “medical protocol”.
Me? I don’t plan to do anything different until we hit about 1000 patients in the USA. That’s about 1/2 a year out. Call it April 15, 2015 or so. A fitting date… That has odds of about 300,000 : 1 on me being too late, and those are OK odds with me. At that point, I cash a chunk of the 401K, buy an RV and a couple of acres out in the boonies, and pack my water purification kit, a load of bleach, and food; and go camping for a year or so…
I don’t expect that to happen, BTW. But it is nice to know when to start taking it seriously. IFF this isn’t ramping down / being quenched, by then, well…. That also lets you know how to evaluate the response of the WHO, CDC, and others. They have 6 months to get their shit together before the shit has hit the fan and you can’t get in front of it. That isn’t a lot of time. I hope they know how to figure doublings…