• EPIDEMICS
• Epidemiological methods
• EPIDEMIOLOGY

The duration and characteristics of the current devastating and unprecedented Ebola epidemic highlight the need for global public health surveillance to establish preparedness mechanisms for future outbreaks. Since the discovery of the virus in 1976, at least 25 Ebola outbreaks have been recorded, on average occurring every 1.5 years with case fatality rate (CFR) between 30% and 90%.1 ,2 The largest interval between two outbreaks is 15 years, that is, from the 1979 outbreak in Sudan due to the Sudan Ebola virus and the subsequent 1994 outbreak in Gabon caused by the Zaire Ebola virus.

Remarkably, only six previous outbreaks generated >100 deaths but the approximately 11 222 deaths (as of 30 June 2015) in the ongoing epidemic is already more than seven times the number of deaths reported for all previous outbreaks combined, which is estimated to be about 1580 deaths.3 ,4 Obviously, the present epidemic is the longest, largest and most complex Ebola outbreak since the virus was first discovered about 40 years ago. The outbreak started in December 2013 in Guinea,2 spread across land borders to Sierra Leone and Liberia, and then subsequently, by some infected persons, to seven other countries (Mali, Nigeria, Senegal, Spain, the UK, Germany and the USA). In some of these countries, individuals were only diagnosed as Ebola virus disease (EVD) cases after their arrival (eg, the USA), while other countries received known patients for treatment (eg, Spain). However, in these countries, the disease was rapidly contained, thanks to improved healthcare facilities, timely patient isolation and treatment. Meanwhile, the outbreak in Guinea, Liberia and Sierra Leone continued on …