Comparing WHO and CDC Projections of Ebola Cases in the Future

Through October  12, 2014, the World Health Organization  (WHO) has reported more than  8900 cases of Ebola since this epidemic began  (link).  The outbreak is currently out of control in three countries in West Africa, Guinea, Liberia, and Sierra Leone.  The graph below depicts the timeline of the growth of the  cumulative number of total cases reported by  each of these countries.  

 

The overall cumulative Ebola case total time series can be fitted to an exponential growth curve to project the total number of cases going into the future. The WHO data indicate that by January  2015 there will be almost 45,000 Ebola cases as shown in the graph below.

 

There is no doubt now that this outbreak will not be contained in West Africa by the end of December.  How many future cases of Ebola will there be is difficult to predict. WHO has noted on several occasions that the officially reported numbers under represent the actual number of cases and deaths in these countries.

On the other hand,  The US Center for Disease Control  (CDC) has projected cases counts ranging from 550,000 to 1.4 million cases in Sierra Leone and Liberia by mid January 2015 (link).  The CDC adjusted  existing case counts by a factor of 2.5 according to their model (as of August 28, 2014).  The graph below compares the differential growth rates based on current WHO data and the estimated case count by the CDC.  According to the CDC estimates, there are now at least 22,000 Ebola cases in West Africa compared to the 8900 reported by WHO.

The graph indicates the clear disparity in the different estimates by these two health agencies of the future case count of Ebola.  As we edge closer to the end of 2014 we will have a better idea of which projection is more accurate.