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Analyzing Ebola – Is it spreading at exponential rate?


We examine how fast Ebola actually spreads in West Africa, and find a very different situation in Liberia, Guinea, and Sierra Leone. Unfortunately, recently it does spread exponentially.



By Gregory Piatetsky, @kdnuggets, Oct 4, 2014.

Ebola is a major global health threat in 2014, but how quickly does it spread? Various news organizations report that the number of cases is increasing exponentially, but there were only a few thousand cases (not millions like for flu), so I decided to investigate from primary data.

I found reports from
 
and extracted data for the 3 most affected countries - Guinea, Liberia, and Sierra Leone.

Of course, the reported numbers should be considered only a lower approximation, since reporting on Ebola is very difficult. The heroic health care workers in West Africa, who collect the data on the ground, face not only the disease (many have already died) but also attacks from scared villagers who think the health care workers spread Ebola. CDC estimates that for every case reported in publicly available case counts, an additional 1.5 cases are not recorded.

More advanced and geographic analysis is possible, as well as looking at lagged time series (since Ebola typically takes about 3 weeks to fully manifest itself), but even our initial analysis is quite illuminating.

First, we see that the disease progression is markedly different in the 3 affected countries.

Ebola cases in West Africa, as of Oct 1, 2014

Fig 1. Total Ebola cases in West Africa, as of Oct 1, 2014

Ebola is clearly spreading the fastest in Liberia, where the number of cases has doubled in about last 25 days. In Sierra Leone, it took about 28 days.

In Guinea, where according to WHO, Ebola started in Dec 2013, we see the earliest cases. However, it seems that the growth rate is slowest there. In fact there was no growth in reported cases in Guinea during July 2-20, with the number of cases stuck at ~ 410, although perhaps this was due to faulty reporting. The growth in reported Ebola cases has resumed in late July, but slower than in the other 2 countries. Still the number of cases has doubled in the last 43 days.

Next graph shows the total number of deaths. Liberia is much harder hit than others.

Ebola cases in West Africa, as of Oct 1, 2014

Fig 2. Total Ebola deaths in West Africa, as of Oct 1, 2014

Finally, we look at the death rate, which again is markedly different - highest in Guinea, lowest in Sierra Leone. One hopeful sign is that % of death in Sierra Leone seems to be decreasing.

Ebola deaths in West Africa, as of Oct 1, 2014

Fig 3. Total Ebola deaths in West Africa, as of Oct 1, 2014

Here is the data in the table form.

Date Guinea
Cases
Guinea
deaths
Liberia
cases
Liberia
deaths
Sierra Leone
cases
Sierra Leone
deaths
1-Oct1199739383420692437623
28-Sep1157710369619982304622
23-Sep1074648354818302021605
21-Sep1022635328016771940597
19-Sep1008632302215781813593
14-Sep942601271014591673562
13-Sep936595240712961620562
7-Sep861557208111371424524
5-Sep812517187110891261491
25-Aug64843013786941026422
20-Aug6074061082624910392
18-Aug579396972576907374
16-Aug543394834466848365
13-Aug519380786413810348
11-Aug510377670355783334
9-Aug506373599323730315
6-Aug495367554294717298
1-Aug485358468255646273
30-Jul472346391227574252
27-Jul460339329156533233
23-Jul427319249129525224
20-Jul415314224127454219
17-Jul410310196116442206
12-Jul406304172105386192
8-Jul40930914288337142
6-Jul40830713184305127
2-Jul41230511575252101
30-Jun4133031076523999
20-Jun390270513415869
16-Jun39826433249749
10-Jun376241131111719
8-Jun372236897
3-Jun344215817
30-May291193506
27-May281186145
21-May258174
10-May233157
3-May231155
29-Apr221146
20-Apr208136
16-Apr197122
10-Apr157101
5-Apr15195
1-Apr12783
31-Mar12280
30-Mar11270
27-Mar10366
25-Mar8660
24-Mar8659