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.

Ebola cases exceed 1000 new cases per week

Based on World Health Organization  (WHO) data, in early September I projected that new Ebola cases would exceed 1000 cases per week by September 21, 2014 (link).  As of the most recent WHO update on September 26, 2014 ( with data current through September 23, 2014), the number of new cases exceeded 1000 in week number 39, starting on September 21. See graph below. 

WHO has not provided a more recent update of the Ebola cases counts. But given the multitude of media reports about many additional uncounted cases and deaths in several of these West African nations, the WHO numbers are probably very low and don't reflect the nature and severity of the Ebola outbreak that is evolving in West Africa.

Ebola infections continue to grow in West Africa

The Ebola epidemic in the three West African countries of Guinea, Liberia, and Sierra Leone continues to grow. As depicted in the graph below,  there have been erratic increases in the number of new Ebola cases in these counties since week number 20 (starting May 11, 2014).

The next graph below, based on the average number of new Ebola cases per week, indicates that the longer term statistical trend in the number of cases is continued exponential increase. The variability in case data from these three countries for week numbers 37 and 38 suggests that local public health officials in these countries can no longer accurately track and count Ebola cases.  Without international support there is no reason to expect that the infection rate will decline any time soon in these countries.

Graph notes: The data used in this graph are derived from World Health Organization and are current through September 16, 2014.  Only cases from the Ebola outbreak in Guinea, Liberia, and Sierra Leone are used in this graph.

H7N9 Cases in China Continue to Increase

On January 24^th,  I posted a graph plotting the growth rate of H7N9 cases in China. Based on the trend (link), I estimated that between 30-40 cases of H7N9 would be reported in the coming weeks. Using current data for onset dates (through February 4, 2014), an updated plot indicates a total of 39 H7N9 cases for both Week 4 and Week 5. More than 30 H7N9 cases (without onset dates) have already been reported for Week 6. If the number of cases continues to increase at an exponential rate, more than 100 people a week will be reported as H7N9 cases by Week 7 or Week 8.  If the rate continues at its current pace, China will be experiencing an H7N9 epidemic within the near future.

Current graph of H7N9 cases through Week 5.