An epidemic of Ebola virus disease (EVD), the most widespread in history, is ongoing in some West African countries.[13][14] It has caused significant mortality, with a reported case fatality rate (CFR) of about 71%.[15][16] It began in Guinea in March 2014 and then spread to Liberia and Sierra Leone.[16] A small outbreak of twenty cases occurred in Nigeria, and one case occurred in Senegal. The latter two countries were declared disease-free on 20 October 2014 after a 42 day waiting period.[8][17][18] Secondary infections of medical workers have occurred in the United States and Spain[19][20] but have not spread further. One case has been identified in Mali[21][22] with as yet no reports of further cases of infection. In August an independent outbreak began in the Democratic Republic of the Congo unconnected to the main epidemic.