The first cases of Ebola disease were reported in Zaire (now known as the Democratic Republic of the Congo [DRC]) in 1976. There were 318 cases and 280 deaths, an 88% case fatality rate.[24]Report of an International Commission. Ebola haemorrhagic fever in Zaire, 1976. Bull World Health Organ. 1978;56(2):271-93.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2395567/pdf/bullwho00439-0113.pdf
http://www.ncbi.nlm.nih.gov/pubmed/307456?tool=bestpractice.com
Transmission in this outbreak was traced back to the use of contaminated needles in an outpatient clinic at Yambuku Mission Hospital. Since then, frequent outbreaks have occurred in Central and Western Africa.[25]Peterson AT, Bauer JT, Mills JN. Ecologic and geographic distribution of filovirus disease. Emerg Infect Dis. 2004 Jan;10(1):40-7.
https://wwwnc.cdc.gov/eid/article/10/01/03-0125_article
http://www.ncbi.nlm.nih.gov/pubmed/15078595?tool=bestpractice.com
The most common species responsible for outbreaks is the Ebola virus (Orthoebolavirus zairense), the second most common species being the Sudan virus (Orthoebolavirus sudanense).
The Ebola virus was responsible for the outbreak that started in West Africa in 2014 and finished in 2016. It was first reported in March 2014, and is the largest outbreak since the virus was first discovered in 1976. Genetic sequencing has shown that the virus isolated from infected patients in the 2014 outbreak is 97% similar to the virus that first emerged in 1976.[26]Centers for Disease Control and Prevention. 2014: CDC laboratories produce first genomic sequence of Liberian Ebola. Mar 2019 [internet publication].
https://archive.cdc.gov/#/details?url=https://www.cdc.gov/amd/whats-new/ebola.html
It has also been responsible for smaller outbreaks in the DRC since then. The virus has a reported case fatality rate of up to 90% in previous outbreaks.[4]Leroy EM, Gonzalez JP, Baize S. Ebola and Marburg haemorrhagic fever viruses: major scientific advances, but a relatively minor public health threat for Africa. Clin Microbiol Infect. 2011 Jul;17(7):964-76.
https://onlinelibrary.wiley.com/doi/10.1111/j.1469-0691.2011.03535.x/full
http://www.ncbi.nlm.nih.gov/pubmed/21722250?tool=bestpractice.com
Direct comparison of case fatality rates between different treatment centers and outbreaks should be interpreted with caution as many variables can introduce bias and skew even large cohort data. The case fatality rate during the 2014 outbreak was up to 64.3% in hospital admissions, falling to 31.5% in some treatment centers in West Africa, and around 20% in patients managed outside West Africa.[18]WHO Ebola Response Team. Ebola virus disease in West Africa: the first 9 months of the epidemic and forward projections. N Engl J Med. 2014 Oct 16;371(16):1481-95.
https://www.nejm.org/doi/full/10.1056/NEJMoa1411100#t=article
http://www.ncbi.nlm.nih.gov/pubmed/25244186?tool=bestpractice.com
[27]Ansumana R, Jacobsen KH, Idris M, et al. Ebola in Freetown area, Sierra Leone - a case study of 581 patients. N Engl J Med. 2015 Feb 5;372(6):587-8.
https://www.nejm.org/doi/full/10.1056/NEJMc1413685
http://www.ncbi.nlm.nih.gov/pubmed/25539447?tool=bestpractice.com
[28]New York Times. How many Ebola patients have been treated outside of Africa? January 2015 [internet publication].
https://www.nytimes.com/interactive/2014/07/31/world/africa/ebola-virus-outbreak-qa.html
In contrast to this, the Sudan virus has a lower case fatality rate of 39% to 65% in previous outbreaks, with the largest outbreak occurring in 2000 in Uganda (425 cases).[4]Leroy EM, Gonzalez JP, Baize S. Ebola and Marburg haemorrhagic fever viruses: major scientific advances, but a relatively minor public health threat for Africa. Clin Microbiol Infect. 2011 Jul;17(7):964-76.
https://onlinelibrary.wiley.com/doi/10.1111/j.1469-0691.2011.03535.x/full
http://www.ncbi.nlm.nih.gov/pubmed/21722250?tool=bestpractice.com
[29]World Health Organization. Disease outbreak news. Ebola disease caused by Sudan ebolavirus – Uganda. January 2023 [internet publication].
https://www.who.int/emergencies/disease-outbreak-news/item/2023-DON433
There has only been one outbreak caused by Bundibugyo virus (Orthoebolavirus bundibugyoense): in 2007 in western Uganda, and this outbreak had a case fatality rate of 25%.[6]Roddy P, Howard N, Van Kerkhove MD, et al. Clinical manifestations and case management of Ebola haemorrhagic fever caused by a newly identified virus strain, Bundibugyo, Uganda, 2007-2008. PLoS One. 2012 Dec 28;7(12):e52986.
https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0052986
http://www.ncbi.nlm.nih.gov/pubmed/23285243?tool=bestpractice.com
Recent outbreaks
2022: an outbreak in Uganda started on September 20, 2022 and was declared over on January 11, 2023, with a total of 142 confirmed cases and 55 deaths (case fatality rate 39%). This was the first outbreak caused by the Sudan virus in Uganda since 2012.[29]World Health Organization. Disease outbreak news. Ebola disease caused by Sudan ebolavirus – Uganda. January 2023 [internet publication].
https://www.who.int/emergencies/disease-outbreak-news/item/2023-DON433
2022: one case was reported in the DRC on August 21, 2022 in the North Kivu province. The case, a 46-year old woman, died after being hospitalized for 23 days for symptoms thought to be related to her known comorbidities.[30]World Health Organization. Disease outbreak news: Ebola virus disease - Democratic Republic of the Congo. Aug 2022 [internet publication].
https://www.who.int/emergencies/disease-outbreak-news/item/2022-DON404
No additional confirmed or probable cases were identified, and the outbreak was declared over on September 27, 2022.
2022: the fourteenth outbreak in the DRC started on April 23, 2022 in the Équateur province and was declared over on July 4, 2022, with a total of 5 cases and 5 deaths (case fatality rate 100%). It was the third outbreak in the province in the last four years.[31]World Health Organization. Ebola virus disease - Democratic Republic of the Congo. Jul 2022 [internet publication].
https://www.who.int/emergencies/disease-outbreak-news/item/2022-DON398
2021: the thirteenth outbreak in the DRC started on October 8, 2021 in the North Kivu province and was declared over on December 16, 2021, with a total of 11 cases and 9 deaths (case fatality rate 82%).[32]World Health Organization. Disease outbreak news. Ebola virus disease – Democratic Republic of the Congo. Dec 2021 [internet publication].
https://www.who.int/emergencies/disease-outbreak-news/item/2021-DON351
2021: a small outbreak was reported in Guinea on February 14, 2021 and was declared over on June 19, 2021, with a total of 23 cases and 12 deaths (case fatality rate 52%). This was the first outbreak in Guinea since the 2014-2016 West Africa outbreak.[33]World Health Organization. Disease outbreak news. Ebola virus disease – Guinea. Jun 2021 [internet publication].
https://www.who.int/emergencies/disease-outbreak-news/item/2021-DON328
2021: the twelfth outbreak in the DRC started on February 7, 2021 in the North Kivu province and was declared over on May 3, 2021, with a total of 12 cases and 6 deaths (case fatality rate 50%).[34]World Health Organization. Disease Outbreak News. Ebola - Democratic Republic of the Congo. May 2021 [internet publication].
https://www.who.int/emergencies/disease-outbreak-news/item/2021-DON325
2020: the eleventh outbreak in the DRC started on June 1, 2020 in the Équateur province and was declared over on November 18, 2020, with a total of 130 cases and 55 deaths (case fatality rate 42%).[35]World Health Organization. Disease outbreak news: Ebola virus disease - Democratic Republic of the Congo. Nov 2020 [internet publication].
https://www.who.int/emergencies/disease-outbreak-news/item/ebola-virus-disease-democratic-republic-of-the-congo-draft
2018-2020: the world’s second largest outbreak in the north Kivu and Ituri provinces of the DRC in 2018 was declared over on June 25, 2020, with a total of 3481 cases and 2299 deaths (case fatality rate 66%).[36]World Health Organization. Ebola health update: north Kivu/Ituri, DRC, 2018-2020. Jul 2020 [internet publication].
https://www.who.int/emergencies/situations/Ebola-2019-drc-
2018: small outbreak in the DRC with 54 cases and 33 deaths (case fatality rate 61%).[3]World Health Organization. Ebola virus disease fact sheet. Apr 2023 [internet publication].
https://www.who.int/news-room/fact-sheets/detail/ebola-virus-disease
2014-2016: the world’s largest outbreak started in the DRC in 2014 and finished in 2016, with over 28,000 cases and 11,000 deaths (case fatality rate 46%).[3]World Health Organization. Ebola virus disease fact sheet. Apr 2023 [internet publication].
https://www.who.int/news-room/fact-sheets/detail/ebola-virus-disease
The WHO declares an outbreak is over when no confirmed or probable cases are detected for a period of 42 days (i.e., twice the maximum incubation period) since the last potential exposure to the last case occurred; however, WHO recommends heightened surveillance and response activities during the 42-day period and for at least 6 months after.[37]World Health Organization. WHO recommended criteria for declaring the end of the Ebola virus disease. Mar 2020 [internet publication].
https://www.who.int/publications/m/item/who-recommended-criteria-for-declaring-the-end-of-the-ebola-virus-disease-outbreak
CDC: ebola outbreak history
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UK Health Security Agency: ebola and Marburg haemorrhagic fevers - outbreaks and case locations
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