The WHO released another report on the status of Ebola in West Africa yesterday. In addition to updating the interactive visualization I created ~2 months ago, I also wanted to bring the charts I posted last week up to speed. As y’all may notice when comparing the 6.19.14 and 6.24.14 fatality figures (below), it appears as if the CFR has dropped ~8% (while the lab-confirmation rate has climbed a bit). This dip in mortality likely has very little to do with improved care-taking; in fact, MSF announced yesterday that it has “reached the limit of what it can do to fight the deadly outbreak“. Instead, the fluctuation we’re seeing right now with CFR (and lab-confirmation rates, for that matter) is due to the following reasons:
1. There exists a lag between when suspected or probable Ebola cases are added to the total tally and when their laboratory results are reported. (This is in part due to the fact that Ebola samples can only be handled in BSL-4 labs.)
2. For many fatal cases, there also exists a second lag between when they are first added to the total tally (soon after they seek treatment for Ebola-like symptoms) and when they die. (This is true for most infectious disease outbreaks; a true CFR statement is hard to establish until the observation period of the disease in question has subsided for all cases tallied. For Ebola, this means that Guinea, Liberia & Sierra Leone need to be free of new cases for ~21 days before the CFR can be calculated with confidence.)
So, what this all means is that both rates – case-fatality and lab-confirmation – will oscillate until the outbreak itself comes to a close. Until then, I’ll update the following charts with regularity to stay on top of the situation as it continues to develop.
Note: Of the outbreaks listed, Zaire ebolavirus [EBOV] is considered to be the causative agent of those denoted with an asterisk.
Historical Data Sources:
 World Health Organization. Ebola haemorrhagic fever in Zaire, 1976. Report of an International Convention. Bulletin of the World Health Organization. 1978;56(2):271-293.
 World Health Organization. Ebola haemorrhagic fever in Sudan, 1976. Report of a WHO/International Study Team. Bulletin of the World Health Organization. 1978;56(2):247-270.
 Heymann DL, Weisfeld JS, Webb PA, et al. Ebola hemorrhagic fever: Tandala, Zaire, 1977-1978. Journal of Infectious Diseases. 1980;142(3):372-376.
 Baron RC, McCormick JB, and Zubeir OA. Ebola virus disease in southern Sudan: hospital dissemination and intrafamilial spread. Bulletin of the World Health Organization. 1983;61(6):997-1003.
 Georges AJ, Leroy EM, Renaud AA, et al. Ebola hemorrhagic fever outbreaks in Gabon, 1994-1997: epidemiologic and health control issues. Journal of Infectious Diseases. 1999;179:S65-75.
 Le Guenno B, Formenty P, Wyers M, et al. Isolation and partial characterisation of a new strain of Ebola virus. Lancet. 1995;345:1271-1274.
 Khan AS, Tshioko FK, Heymann DL, et al. The Reemergence of Ebola Hemorrhagic Fever, Democratic Republic of the Congo, 1995. Journal of Infectious Diseases. 1999;179:S76-S86.
 World Health Organization. Ebola haemorrhagic fever – South Africa. Weekly Epidemiological Record. 1996;71(47):359.
 Okware SI, Omaswa FG, Zaramba S, et al. An outbreak of Ebola in Uganda. Tropical Medicine and International Health. 2002;7(12):1068-1075.
 World Health Organization. Outbreak(s) of Ebola haemorrhagic fever, Congo and Gabon, October 2001- July 2002. Weekly Epidemiological Report. 2003;78(26):223-225.
 Formenty P, Libama F, Epelboin A, et al. Outbreak of Ebola hemorrhagic fever in the Republic of the Congo, 2003: a new strategy? Medecine Tropicale (Marseille). 2003;63(3):291-295.
 World Health Organization. Ebola haemorrhagic fever in the Republic of the Congo – Update 6. Weekly Epidemiological Record. 6 January 2004.
 World Health Organization. Outbreak of Ebola haemorrhagic fever in Yambio, south Sudan, April-June 2004. Weekly Epidemiological Record. 2005;80(43):370-375.
 MacNeil A, Farnon EC, Morgan OW, et al. Filovirus Outbreak Detection and Surveillance: Lessons from Bundibugyo. Journal of Infectious Diseases. 2011;204:S761-S767.
 World Health Organization. End of the Ebola Outbreak in the Democratic Republic of the Congo. Global Alert and Response. 17 Febuary 2009.
 Shoemaker T, MacNeil A, Balinandi S, et al. Reemerging Sudan Ebola Virus Disease in Uganda, 2011. Emerging Infectious Diseases. 2012;18(9):1480-1483.
 Albarino CG, Shoemaker T, Khristova ML, et al. Genomic analysis of filoviruses associated with four viral hemorrhagic fever outbreaks in Uganda and the Democratic Republic of the Congo in 2012. Virology. 2013;442(2):97-100.