Random Analytics: Top 10 Ebola Outbreaks and West Africa

by Shane Granger

After a six month sabbatical I’m dipping my toe back into Random Analytics (and by default my passion for amateur epidemiology).

Last week the World Health Organisation released its latest Ebola Situation Report – 15 July 2015 which has demonstrated that although the disease has stopped it momentous attrition within West Africa it hasn’t entirely gone away. As we learnt from the initial outbreak in late 2013 one case can turn into many hundreds, then many thousands and finally some tens of thousands in a very short space of time.

The WHO notes:

There were 30 confirmed cases of Ebola virus disease (EVD) reported in the week to 12 July: 13 in Guinea, 3 in Liberia, and 14 in Sierra Leone. Although the total number of confirmed cases is the same as the previous week, there has been a shift in the foci of transmission. For the first time in several months, most cases were reported from Conakry and Freetown, the capitals of Guinea and Sierra Leone, respectively. All 9 of the cases reported from Conakry and all 10 of the cases reported from Freetown were either registered contacts of a previous case or have an established epidemiological link to a known chain of transmission. One of the 30 cases reported in the week to 12 July arose from a yet unknown source of infection. However, a substantial proportion of cases (7 of 30: 23%) continue to be identified as EVD-positive only after post-mortem testing. This suggests that although improvements to case investigation are increasing our understanding of chains of transmission, contact tracing, which aims to minimise transmission by identifying symptoms among contacts at the earliest stage of infection, is still a challenge in several areas.

As the following chart demonstrates the 2013-15 West African Ebola Zaire outbreak has eclipsed all previous Ebola events.

1 - Ebola_Top10Outbreaks_150717

Even as the disease has left the pages of most Western newspapers and television screens the scale of the event and the ongoing transmission is still frightening. Consider just these three data points:

  1. Based on current Case Numbers alone the West African outbreak is 65-times greater than the next largest outbreak (the Ebola Sudan outbreak in Uganda in 2000);
  2. The West African outbreak currently is 11-times greater than ALL previous outbreaks combined (total cases prior to the West African plus the 2014 DRC outbreak totalled 2470 while the current outbreak cases total 27,678);
  3. In the past week of reporting the total case count (30) was just under half of the 10th worst outbreak of Ebola recorded in Gabon back in 2001 and greater than the 13 of the 30 historical outbreaks/events across the world to date.

Not all of us have forgotten West Africa.


Data Sources

[1] WHO. Ebola Situation Report – 15 July 2015. Accessed 17 July 2015.