Epidemiology of Ebola virus disease outbreak in West Africa, 2013-2014

Objective To understand the epidemiological characteristics of Ebola virus disease (EVD) in West Africa in 2014 and to provide scientific evidences for EVD prevention in China. Methods Descriptive epidemiological analysis was conducted on the EVD epidemic data published by World Health Organization. Results A total of 4985 EVD cases, including 2461 deaths, were reported in Guinea, Liberia, Sierra Leone, Nigeria and Senegal from December in 2013 to 13 September in 2014. The case fatality rate was 49%. Until now, 2 stages of epidemic have been observed, the first one was characterized by the outbreak in Guinea from December 2013 to April 2014; and the second one was from May to August in 2014 when the disease spread in Guinea, Liberia, and Sierra Leone. Except Nigeria, the other four countries bordered each other. The secondary transmission in Nigeria was caused by an EVD case imported from Liberian, and the secondary transmission reported by Senegal was caused by an EVD case from Guinean. As of September 13, nearly 300 health-care workers have been infected in the five countries (nearly 6% of total cases), in which more than 140 died. Genetic analysis indicates that the virus caused this outbreak is a separate clade of the Zaire ebolavirus (EBOV). Conclusion The public health emergency of Ebola virus disease (EVD) occurring in West Africa in 2014 is not only the largest outbreak since the Ebola virus was first discovered in 1976, but also the first report of EVD outbreak in West Africa. The outbreak might last for 6 to 9 months from now on.