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Epidemiological update: outbreak of Ebola virus disease in West Africa

10 Oct 2014

​Event background information

Chronology of events – key dates

22 March 2014: the Guinea Ministry of Health notified WHO about a rapidly evolving outbreak of EVD [1]. The first cases occurred in December 2013. The outbreak is caused by a clade of Zaïre ebolavirus that is related but distinct from the viruses that have been isolated from previous outbreaks in central Africa, and clearly distinct from the Taï Forest ebolavirus that was isolated in Côte d’Ivoire from 1994–1995 [2-4]. The first cases were reported from south-eastern Guinea and the capital Conakry.

May 2014: the first cases were reported from Sierra Leone and Liberia [5,6] to where the disease is assumed to have spread through the movement of infected people over land borders.

End of July 2014: a symptomatic case travelled by air to Lagos, Nigeria, where he infected a number of healthcare workers and airport contacts before his condition was recognised to be EVD.

8 August 2014: WHO declared the outbreak a Public Health Event of International Concern (PHEIC) [7] and confirmed on 22 September that the 2014 Ebola outbreak in West Africa continued to constitute a Public Health Emergency of International Concern.

29 August 2014: the Ministry of Health in Senegal reported a confirmed imported case of EVD in a 21-year-old male native of Guinea.

18 September 2014: the United Nations Security Council recognised the EVD outbreak as a 'threat to international peace and security' and unanimously adopted a resolution on the establishment of an UN-wide initiative which focuses assets of all relevant UN agencies to tackle the crisis [8].

23 September 2014: A study published by the WHO Ebola response team forecasted more than 20 000 cases (5740 in Guinea, 9890 in Liberia, and 5000 in Sierra Leone) by the beginning of November 2014 [9]. The same study estimated the doubling time of the epidemic at 15.7 days in Guinea, 23.6 days in Liberia, and 30.2 days in Sierra Leone.

30 September 2014: the US Centers for Disease Control and Prevention (CDC) announced the first imported case in US of Ebola linked to the current outbreak in West Africa.

3 October 2014: In Senegal, all contacts of the imported EVD case have completed a 21-day follow-up period. No local transmission of EVD has been reported in Senegal.

6 October 2014: The Spanish authorities reported a confirmed case of Ebola virus disease (EVD) of a healthcare worker who participated in the treatment in Spain of the second Spanish patient with Ebola infection repatriated to Spain.

Epidemiological update

Situation in West Africa

Since December 2013 and as of 5 October 2014, 8 032 cases of EVD, including 3 865 deaths, have been reported by WHO (Figure 1) [10].

The distribution of EVD cases by affected countries is as follows and is presented in figure 1:

  • Guinea: 1 298 cases and 768 deaths as of 5 October 2014;
  • Liberia: 3 924 cases and 2 210 deaths as of 4 October 2014;
  • Sierra Leone: 2 789 cases and 879 deaths as of 5 October 2014;
  • Nigeria: 20 cases and 8 deaths, with last confirmed case in Lagos on 5 September 2014 (30 days as of 5 October 2014) and in Rivers State on first September 2014 (34 days as of 5 October);
  • Senegal: 1 case, no deaths, confirmed on 28 August 2014 (38 days as of 5 October). All contacts have completed 21 days of follow-up.
 
Figure 1. Distribution of cases of EVD by week of reporting in Guinea, Sierra Leone, Liberia, Nigeria and Senegal, weeks 48/2013 to 41/2014, n=8 032*

* The bar for week 41/2014 does not represent a complete week. The solid green line represents the trends based on five week moving average plotted on the fifth week of the moving average window. The figure includes one imported case in Senegal.
 
The WHO Ebola response team showed that the current EVD cases present a similar course of infection, signs and symptoms when compared to previous outbreaks of EVD [9]. The incubation period was estimated to be 11.4 days with serial interval of 15.3 days.
 
The case-fatality rate estimated among 4 010 cases with known clinical outcome in Guinea, Liberia and Sierra Leone was 70.8% (95% CI: 68.6–72.8%) with no noticeable difference between the countries.
 
 
Situation in Guinea, Sierra Leone and Liberia
 
Guinea, Liberia and Sierra Leone are experiencing widespread intense transmission as per WHO categorisation [10]. The outbreak is still evolving in these three countries (Figures 2 and 3). Officially reported figures are believed to be underestimates [9]. The Guinean prefecture of Lola located in the Nzérékoré Region and bordering Ivory Coast was added to the list of affected areas on 2 October 2014 with 9 suspected cases reported, including 2 cases confirmed by the Guinean Ministry of Health.

Figure 2. Distribution of cases of EVD by week of reporting in the three countries with widespread and intense transmission as of week 41 2014, n= 8 011*
 

* The bar for week 41/2014 does not represent a complete calendar week. Source: Data are based on official information  reported by Ministries of Health up to the end of 5 October for Guinea and Sierra Leone, and 4 October for Liberia. [10]


Figure 3. Distribution of cases of EVD by week of reporting in Guinea, Sierra Leone, Liberia and Nigeria (as of week 40/2014)


Source: Data from ministry of health reports (probable and confirmed cases).
 
Situation in Nigeria
 
As of 3 October 2014, 20 cases, including eight deaths have been notified. The date of the last confirmed case in Lagos was on 5 September 2014 and in Rivers State on 1 September 2014 [11]. All 891 identified contacts in Nigeria have completed the 21-day follow-up (362 contacts in Lagos, 529 contacts in Port Harcourt) [10].
 
Situation among healthcare workers in West Africa
 
As of 5 October 2014, WHO reported 401 healthcare workers infected with EVD of which 232 died [10]. Table 2 details the distribution of cases and deaths among healthcare workers in the four affected countries.
 
Table 1. Number of Ebola cases and deaths in healthcare workers (HCW) in West Africa
 
Country
HCW cases
(% of reported cases)
HCW deaths
(% of reported deaths)
Guinea
 73 (5.6)
38 (4.9)
Sierra Leone
 129 (4.6)
95 (10.8)
Liberia
188 (4.8)
94 (4.3)
Nigeria
11 (55.0)
11 (55.0)
Total
401 (5.0)
232 (6.0)
Source: data are based on official information reported by Ministries of Health as of 5 October for Guinea and Sierra Leone and 4 October for Liberia. [10]
 
Situation outside of West Africa
 
United States of America
 
On 30 September 2014, the US CDC announced the first imported case of EVD linked to the current outbreak in West Africa. The individual who had recently arrived from Liberia was diagnosed in Dallas, Texas. This person is not a healthcare worker and was visiting relatives in the USA. He is reported to have had a high risk exposure in Liberia prior to travelling. He was reported to be asymptomatic when leaving West Africa and remained asymptomatic while travelling and upon arrival in the USA on 20 September. He developed symptoms around 24 September, sought medical care on 26 September and was hospitalised and isolated on 28 September 2014. He died on 8 October 2014.
 
The US health authorities are investigating contact persons who may be at risk of infection from this patient. This excludes people that were on the same commercial airlines as the person was asymptomatic while travelling from Liberia to the USA. The person reported developing symptoms only several days after the flights and therefore was not contagious during that period. 
 
As of 7 October 2014, the US CDC reports that the investigation of 10 contact persons with definite exposure to the case and 38 persons with possible exposure is ongoing. It is reported for daily monitoring to be made with contacts for up to 21 days after exposure to the case to check for fever and other symptoms [12]. 
 
Spain
 
On 6 October, Spanish authorities reported a confirmed case of EVD in a healthcare worker who participated in the medical care of the second Spanish patient repatriated to Spain with Ebola infection. The medically evacuated patient arrived in Spain on 22 September and died on 25 September. Yet, the infected healthcare worker represents the first transmission of Ebola infection outside of west Africa region Union [13]. 
 
The healthcare worker is a woman working in La Paz-Carlos III hospital in Madrid. She reportedly developed fever the night of the 29 September. According to the Spanish Ministry of Health, she participated in the medical care of the repatriated patient and was wearing appropriate personal protection equipment. She was admitted to La Paz-Carlos III Hospital on 6 October and is under strict isolation [14].
 
The Spanish authorities have initiated contact tracing and, as of 9 October, 58 contacts of which five are considered as high-risk contacts, are being monitored. Quarantine has been established or is under assessment for high risk contacts.
 
Preliminary results of the investigation point to an incident during the removal of the personal protection equipment (PPE) on 24 September as the mode of transmission.
 
Medical evacuations from EVD-affected countries
 
Fourteen of Ebola virus infected individuals have been evacuated from the EVD-affected countries (Table 2, Figure 4).
 
Table 2. Medical evacuation from EVD-affected countries up to 08 October 2014
 

Date of evacuation

(in 2014)

Evacuated from

Evacuated to

Profession

Status

Confirmed

Citizenship

02 August 2014

Liberia

Atlanta (USA)

Healthcare worker

Discharged

Yes

US

05 August 2014

Liberia

Atlanta (USA)

Healthcare worker

Discharged

Yes

US

06 August 2014

 Liberia

Madrid (Spain)

Healthcare worker

Death

Yes

Spanish

24 August 2014

Sierra Leone

London (United Kingdom)

Healthcare worker

Stable

Yes

British

27 August 2014

Sierra Leone

Hamburg (Germany)

Epidemiologist

Recovered

Yes

Senegalese

04 September 2014

Monrovia, Liberia

Omaha, Nebraska (USA)

Physician (obstetrician)

stable

Yes

US

09 September 2014

Kenema, Sierra Leone

Atlanta, Georgia (USA)

Physician

stable

Yes

US

14 September 2014

Sierra Leone

Leiden (The Netherlands)

Healthcare worker

Discharged

No

Dutch

14 September 2014

Sierra Leone

Leiden (The Netherlands)

Healthcare worker

Discharged

No

Dutch

19 September 2014

Liberia

Paris (France)

Healthcare worker

Discharged

Yes

French

22 September 2014

Sierra Leone

Madrid (Spain)

Healthcare worker

Serious condition

upon evacuation

Yes

Spanish

22 September 2014

Sierra Leone

Lausanne (Switzerland)

Healthcare worker

Admitted

Unknown

Non-Swiss

28 September 2014

Sierra Leone

Maryland (USA)

Healthcare worker

Admitted

Unknown

US

02 October 2014

Sierra Leone

Frankfurt (Germany)

Healthcare worker

stable

Yes

Uganda

02 October 2014

Liberia

(USA)

Cameraman

Stable

Yes

US

06 October 2014

Sierra Leone

Oslo (Norway)

Healthcare worker

not known

Yes

Norway

08 October 2014

Liberia

Leipzig (Germany)

Laboratory worker

not known

Yes

Sudan


 
Figure 4. Medical evacuation from EVD-affected countries, as of 8 October 2014
 
 
 

Download the data:

 
The following data are available to download as .csv files. 
 
 
  • EVD epicurve data
    Cumulative number of cases and deaths for the five West African countries with reported EVD cases (Liberia, Guinea, Sierra Leone, Nigeria, Senegal). Source: WHO
  • EVD map data
    Cumulative number of cases and deaths at subnational level of the five West African countries with reported EVD cases (Liberia, Guinea, Sierra Leone, Nigeria, Senegal). Source: National situation report
    For those weeks without reported data, the most recent figures were used as best estimate of the number of case).


References
1. World Health Organization. Ebola virus disease in Guinea [Internet]. Geneva: WHO; 2014 Mar 23 [cited 2014 Oct 8]. Available from: http://www.who.int/csr/don/2014_03_23_ebola/en/.

2. World Health Organization. Ebola virus disease - Fact sheet No103. [Internet]. Geneva: WHO; 2014 [updated 2014 Sep; cited 2014 Oct 8]. Available from: http://www.who.int/mediacentre/factsheets/fs103/en/.
3. Baize S, Pannetier D, Oestereich L, Rieger T, Koivogui L, al. e. Emergence of Zaire Ebola Virus Disease in Guinea. N Engl J Med [Internet]. 2014 Apr 16. Available from: http://www.nejm.org/doi/full/10.1056/NEJMoa1404505.
4. Muyembe-Tamfum JJ, Mulangu S, Masumu J, Kayembe JM, Kemp A, Paweska JT. Ebola virus outbreaks in Africa: past and present. Onderstepoort J Vet Res. 2012;79(2):451.
5. Centers for Disease Control and Prevention. Ebola in Liberia [Internet]. Atlanta: CDC; 2014 [cited 2014 Aug 26]. Available from: http://wwwnc.cdc.gov/travel/notices/alert/ebola-liberia.
6. Centers for Disease Control and Prevention. Ebola in Sierra Leone [Internet]. Atlanta: CDC; 2014 [cited 2014 Sep 30]. Available from: http://wwwnc.cdc.gov/travel/notices/alert/ebola-sierra-leone.
7. World Health Organization. WHO statement on the meeting of the International Health Regulations Emergency Committee regarding the 2014 Ebola outbreak in West Africa [Internet]. Geneva: WHO; 2014 [cited 2014 Aug 29]. Available from: http://who.int/mediacentre/news/statements/2014/ebola-20140808/en/.
8. United Nations Security Council. Resolution 2177 (2014). Adopted by the Security Council at its 7268th meeting on 18 September 2014 [Internet]: UN; 2014 [cited 2014 Oct 8]. Available from: http://www.ifrc.org/docs/IDRL/UN%20SC%20Res.pdf.
9. WHO Ebola Response Team. Ebola Virus Disease in West Africa — The First 9 Months of the Epidemic and Forward Projections. N Eng J Med [Internet]. 2014 Sep 23 [cited 2014 Sep 30]. Available from: http://www.nejm.org/doi/full/10.1056/NEJMoa1411100.
10. World Health Organization. Ebola response roadmap situation report. 8 October 2014. [Internet]. Geneva: WHO; 2014. Available from: http://apps.who.int/iris/bitstream/10665/136020/1/roadmapsitrep_8Oct2014_eng.pdf?ua=1.
11. World Health Organization. Ebola response roadmap situation report. 3 October 2014 [Internet]. Geneva: WHO; 2014. Available from: http://apps.who.int/iris/bitstream/10665/135765/1/roadmapupdate3oct14_eng.pdf?ua=1.
12. Centers for Disease Control and Prevention. First Imported Case of Ebola Diagnosed in the United States [Internet]. Atlanta: CDC; 2014 [cited 2014 Oct 8]. Available from: http://www.cdc.gov/vhf/ebola/outbreaks/2014-west-africa/united-states-imported-case.html#ebola-contact-tracing.
13. Ministerio de Sanidad Servicios Sociales e Igualdad. Diagnosticado un caso secundario de contagio por virus Ébola [press release in Spanish] [Internet]. 2014 [cited 2014 Oct 6]. Available from: http://www.msssi.gob.es/gabinete/notasPrensa.do?id=3427.
14. Ministerio de Sanidad Servicios Sociales e Igualdad. Sanidad y la Comunidad de Madrid constituyen una Comisión de coordinación para realizar el seguimiento del virus Ébola [press release in Spanish] [Internet]. 2014 [cited 2014 Oct 7]. Available from: http://www.msssi.gob.es/gabinete/notasPrensa.do?id=3428
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