People like numbers. Even people who don't like math like numbers. They're simple things that we can relate to, to put everything in perspective. 3 is less than 4, 4 billion is more than 4 million, $5,000,000 is a lot of money, 200 miles is a few hours of driving. They're immobile--etched in stone--and usually don't need to be critically analyzed. Numbers can be used IN critical analysis (they usually should be) and you can analyze the factors/causes that generate the numbers, but unless you're a number theorist you usually you don't need to analyze the number itself.
So these are easy things for the mass media--nationally and internationally (numbers are universal, of course) to serve to the public in easily-consumed ways that will encourage them to watch their news reports, and to repeat these reports to others who will, in turn, also watch said news reports. They encapsulate information in easily digestible packets that we can eat up, without thinking about them too much--if at all.
We're seeing a lot of this with Ebola. It's an infectious disease, something that falls within the science of epidemiology, and is thus subject to a whole mess of numbers that make something extraordinarily complex a bit easier to understand. However the ways in which these numbers are wantonly tossed around, to a public that doesn't really understand their significance, can be a real problem.
So what are some numbers that we've been hearing about Ebola--that many of us have memorized at this point? Here's some of the more popular examples:
1.4 MILLION (a CDC "projection" of Ebola cases by Jan. 20)
10,000 cases PER WEEK (a World Health Organization warning a few days ago of a possible impending increase in cases)
3-4 week DOUBLING TIME (this in context of the world's introduction to the "exponential" function)
R0 = 2 (i.e. one person may be expected to infect 2 others)
2.5 (factor by which actual cases may exceed WHO's recorded likely cases)
Now--none of these are inherently incorrect. After all, they've all been put out there by leading organizations. But a public eager for simple metrics usually doesn't critically analyze where these numbers come from, either. So it's easy to latch on to the big, frightening onces, and become terrified.
So below the fold I'll mention a bit about these numbers, and direct you to a model (not THE model, but a similar one) from which such numbers may arise, and mention a couple reasons why we can perhaps allow ourselves a bit of optimism.
Over the fold....
First, the numbers: I'll sum these up quickly.
1.4 Million: This was a CDC projection, from September (I believe) on what an exponential increase in Ebola cases could yield without any intervention, by Jan. 20. It anticipates rapidly degraded services, zero intervention, complete collapse in health care services and in general social infrastructure more generally. It disregards Cuban doctors, Chinese experimental drugs, U.S. troops/treatment centers, etc. It suggests that, by Dec. 20 (or so) we'd be at around 700,000 cases. I'm not sure if these numbers are based on documented cases or if they include unknown cases (which could, as above, be some 2.5X the known cases) but even if we include that factor then we still have around 20-25,000 cases in W. Africa to date, accounting for unknown cases. These case counts suggest that we won't be within orders of magnitude of that complete worst-case-scenario number.
But in any case, the CDC never said "We'll have 1.4 million cases by Jan. 20". They said "If the world completely turns its back and we let everything collapse, we could hit that number. So anyone still citing that metric can really stop--it's old, fortunately unrealized, and unhelpful at this point.
10,000 cases per week
This was WHO's warning a few days ago--and I believe they said 5-10,000 cases per week (of course the media will report the top number). This I believe reflects reported cases and does NOT take the 2.5x factor into account, but it, again, is based again on worst-case scenarios of no increased intervention. This was effectively part of an appeal for more help, a caution of what COULD happen if the International Community doesn't "step up". (they are--but still not fast enough).
From late August through mid September we were seeing increases of about 600-700 cases a week. This has increased to around 900 from Mid-Sept. through mid-October. So although reported cases are indeed increasing (as expected), it would seem that increased intervention is slowing down that increase. That suggests that WHO's cautionary high-end estimate of 5-10,000 cases per week is very, very unlikely to develop based on current trajectories. My guess is that, since we are dealing with an exponential curve (even though our intervention seems to be influencing/lowering that exponent), we will see weekly increases. Perhaps by late November we will indeed have 2,000 additional cases a week. But I don't see any way that this particular worst-case-scenario projection is going to come to pass within 2 months.
That doesn't mean such an increase won't happen later..
But there will be more time for preparation, distribution of resources, etc.
3-4 week doubling time
This is a commonly cited metric, and it was accurate awhile ago. In August/early September we WERE seeing around a 3-4 week doubling time--we were at around 3,700 known cases at the beginning of September, increasing at perhaps 700 cases a week (I believe the Sept. 16-24 week may have seen in increase of around 950). But this hasn't been constant the last few weeks. For example, at the beginning of October we were at around 7,500 cases (up to 8011 on Oct. 5) and now we're at about 9,500 (9190 as of Oct. 14).
So that suggests that the end of October will not have double the caseload as the end of September (current projections put it somewhere around 11-12,000 by Oct. 31)
So while this is, of course, terrible for W. Africa, it is NOT a 3-4 week doubling time--at least right now. It was, earlier, but it seems like we've been having some impact.
Now, a caveat here: these estimates are based on WHO documented cases (likely/probable--of which lab-tested results are only about 60% of this) As health-care gets overloaded, we may expect to see lapses in the testing. But it's in indicator of possible progress...I'm not an epidemiologist so I can't offer too many specifics. But I'll talk about this a bit more below.
Now, a couple more numbers:
R0 = 2, and the 2.5 factor--I can't comment specifically on what the R nought actually is estimated at at the moment--although I think I recalls seeing that for the Ebola virus it tends to be around 1.5-2, so each person could be expected to infect 1.5-2 additional persons, on average.
Now, I've seen some people somewhat breathlessly say "But R nought is actually 2 HERE IN THE U.S.!!! We're doomed!!" Well, yes, that's technically true (the R value--not the doom). Of course that takes a single data point into account, a person who happened to infect two of the people who would be mostly likely to be directly involved with bodily fluids at peak virulence of the disease--and who, as we now know, were not well trained or protected, this isn't paritcularly shocking. If 6 people on the Cleveland plane get Ebola, then we'll have other things to talk about. But that's extraordinarily, exceedingly unlikely. If it WERE likely, I think we'd have had a horrible epidemic of Ebola in Lagos by now. But even there--the cases were, as I understand it, primarily health care workers--perhaps one or two other people. And the fact that as yet there are no symptoms from Duncan's family. Which all goes to confirm what the CDC/WHO have been telling us--that Ebola is really NOT very easy to catch.
As for the 2.5 factor, that actual infections are 250% of what's actually been reported, that's certainly plausible and wouldn't surprise me. And it certainly increases all of the numbers I mentioned above--but not by orders of magnitude.
But I don't have any additional data on that.
***********************
Models, the WHO, and some signs of progress
Ok, so there's some insight on the numbers. Now take a look at this fantastic model by Columbia University Here
You can look at the graphs (based on WHO probable/likely cases) or a data table, for each country, or all three--Liberia, S.L. and Guinea. You can also select for "No change", "Degraded" or "improved" scenarios to see how that affects predicted infections.
For the "no change" option--meaning that resources continue as they have for a while, the model predicts that there could have been around 18,000 cases by Oct. 12--instead we have around 9,200. Extrapolating through the end of november, the same scenario (no change) predicts some 25,000 cases (this may be based on recently updated changes in the model based on current resources, that's why it's not higher--but I"m not sure). However our current rates of increase--even if they jump a bit, put us at around 20,000 or less by the end of November--not the 25-30,000 that a "no change" model would predict.
However, the bad news is that if we had been following the "Improved" model, we should be a bit over 7,000 now: instead we're at well over 9,000, and by the end of November an "improved model" would have us at 14,000 cases, whereas it looks like we'll be closer to 20,000.
However, if the whole damn system collapsed completely and we experienced rapid degradation, then we could have expected over 100,000 cases by end of November.
The bottom line is that the numbers suggest that global investment is having some effect, but NOT YET ENOUGH. We're consistently riding the line between the "no change" and 'Improved" models--which is not good enough. Also, reports are suggesting that conditions are actually deteriorating in Guinea--but that they may be improving in Liberia (although because of the high case-load it's hard to tell for certain) and remain somewhat constant in S.L. Some of the outbreak hotspots are seeing possible declines--but transmission within the capitals continues at a fast pace.
So it's really hard to say exactly what's going on--just that we're having some effect but have an extraordinary amount still to do.
Now, some additional thoughts:
********************
Borders and Movement
There's been a lot of discussion about closing borders, restricting flights--and I'll admit I've gone back and forth on this, in part because I've seen the way that we in the U.S. really botched our first case. Now, FOX/Drudge/etc. have been crowing about how "Even African countries are shutting their borders!!!!'
Like the numbers, this is inherently true, but Fox/Drudge (as expected) aren't telling the full story. The countries that are closing their borders are also resource impaired, they are (in many case) right next door to outbreak-riddled areas, the borders are often very porous, so they have an enormous amount to lose if unaccounted refugees move into their countries. It would be easy for a similar outbreak to develop in, say, Cote D'Ivoire or the Gambia. It's understandable, and these border closings have indeed had an effect. The facts that a.) the disease still hasn't spread b.) that Senegal and Nigeria mobilized resources extremely effectively, and c.)there are more resources in place in the region, is encouraging.
So African border closings do seem to have been a good move.
Here, though the situation is very different. Although the African caseload has increased, it is not by orders of magnitude (6,000 in september, 9,000 now are comparable numbers) There has only been a single [known] person--Mr. Duncan, who slipped through the monitoring cracks and sadly didn't receive the treatment he could have. We didn't see Ebola flareups everywhere in the world in September. There may be a few other cases now--but it seems that we can expect a trickle rather than a flood. Practically all cases treated outside of Africa were diagnosed IN AFRICA and flown elsewhere for treatment--exceptions being Duncan and the 3 transmissions as a result of poor practice in Spansh and American hospitals. Despite problems in the U.S. and Spain, so-called "first world" countries generally seem to have a handle on this. The U.S. too--we've handled Ebola before and we have I believe 6 or 7 patients here now who are in recovery. If these patients make it (and I hope to god they do--it's looking promising), that suggests that treatment in our and European hospitals is increasing the survival rate--still high, but perhaps 25-30% rather than 70. So despite the mistakes, lots of positive outlooks for treatment outside of Africa.
Now, as i mentioned above, if we get a few cases from the Cleveland flight, we'll have to rethink things--particularly about probability of transmission--but right now things are generally encouraging.
Elsewhere, there is a reasonable fear of transmission in overly crowded, largely poverty-stricken cities like Calcutta, or Karachi, or (again) Lagos, or any other large city in an underdeveloped region. Political instability doesn't help either (e.g. Congo, Nigeria, Mali at times) That's true--and it's something the WHO is certainly watching out for. But we are far more aware than we were a few months ago, and that should be a good thing.
So ultimately, while concern and most definitely warranted, and a good motivator in places like West Africa, there are encouraging signs even for the region, and definitely encouraging signs that most areas of the global community will be able to put out any small Ebola fires that do pop up.
1:02 PM PT: Commenter InclusiveHeart makes a worthwhile point:
Hopefully, we are going to avoid that January 20 1.4 million mark by working to stop the epidemic in West Africa. However, I am very glad that the CDC published that prediction at the time because few in the world were taking what was going on in West Africa when it was released. It served its purpose.
And today we're seeing this again today with Oxfam saying that this could be "the disaster of our time". So there is definitely strong language being used---and it's a powerful motivating factor. Message being "act NOW, or we've got a monumental problem on our hands".
This is good messaging--encouraging help where it's needed. Contrast this with the U.S. media messaging which is manipulating these numbers to make you think that you--YES YOU could die. "CDC SAID 1.4 MILLION--CLOSE BORDERS FROM AFRICANS AND ISIS WITH EBOLA NOW BEFORE THEY TEAM UP WITH MEXICAN DRUG LORDS TO DIRTY-BOMB THE COUNTRY!!"
That's not what CDC, or the WHO, or OXFAM wants from their warnings--they're tryihng to get help for West Africa which is desperately needed.
1:24 PM PT: 2nd update: Although the weekly increase has been hovering at under 1,000 (which is lower than it could have been and is potentially a good thing), remember that the while the increase in infections is exponential, the increase in resources is NOT. So even if we're seeing an increase that's become almost linear for a few weeks--we're hardly out of the woods--because the resources required to take care of a each additional 1,000 patients is enormous--and infections happen faster than recoveries (or, unfortunately, deaths). So we can expect the curves to bounce around a lot and it's imperative to keep them under control.