Initial outbreak of new Ebola strain in Guinea

1. This investigation documents the initial phase of the Ebola outbreak in Guinea, with the initial case being a 2 year-old from Guéckédou prefecture.

2. The strain of Zaire ebolavirus isolated in the current outbreak is distinct from strains implicated in previous outbreaks in the Democratic Republic of Congo and Gabon.

3. As of September 2014, the current outbreak of Zaire ebolavirus has led to over 5,300 cases and over 2,600 deaths in sub-Saharan Africa.

Evidence Rating Level: 4 (Below Average)

Study Rundown: Ebola virus is a major public health concern in sub-Saharan Africa, as infection is associated with case-fatality rates between 30 to 90% depending on the species of the virus. Previous outbreaks had been limited in geographic scope and to several hundred cases at the most. In March 2014, the World Health Organization declared a large Ebola outbreak in Guinea. There have since been over 5,300 confirmed, probable, or suspected cases and over 2,600 deaths in Guinea, Liberia, Sierra Leone, Senegal, and Nigeria, more than all previous outbreaks combined. The duration and geographic spread of this Ebola outbreak is unprecedented, and WHO has since declared it an international emergency.

This study documents the initial phase of the outbreak in several prefectures of Guinea. Zaire ebolavirus (EBOV) was identified as the causative agent, though phylogenetic analysis showed this was distinct from previous strains causing outbreaks in the Democratic Republic of Congo and Gabon. The epidemiologic investigation traced the origins of the outbreak to a 2 year-old who died in Guéckédou prefecture on December 6, 2013.

Click to read the study in NEJM

Click to read an accompanying editorial in NEJM

Relevant Reading: Ebola haemorrhagic fever

In-Depth [epidemiologic investigation]: In March 2014, the Ministry of Health of Guinea was notified of an unknown disease causing numerous deaths in Guéckédou and Macenta prefectures. An epidemiologic investigation was launched by the Ministry of Health and Médecins sans Frontières days later. This study documented the initial phase of the EBOV outbreak.

Blood samples were drawn from 20 patients in Guéckédou, Macenta, and Kissidougou who presented with fever, diarrhea, vomiting, or hemorrhage. Using several reverse-transcriptase polymerase-chain-reaction (RT-PCR) assays, 15 of the 20 patients were confirmed to have EBOV. Three patients were identified as having high levels of EBOV RNA through RT-PCR, and these EBOV genomes were completely sequenced using conventional Sanger techniques (given GenBank accession numbers KJ660346, KJ660347, and KJ660348). The three sequences were 18,959 nucleotides in length and were identical apart from 6 polymorphisms. Phylogenetic analysis demonstrated that this Guinean EBOV occupied a separate, basal position within the EBOV clade.

Information regarding transmission chains was collected through reviewing hospital records, and interviewing patients with suspected EBOV, patient contacts, health authorities, and healthcare workers. The case-fatality rate of these initial cases was found to be 86%, as 12 of 14 patients with a known outcome died. The epidemiologic investigation determined that the suspected first case of the outbreak (S1) was a 2 year-old who died in Guéckédou on December 6, 2013, and that patient S14 was a healthcare worker from Guéckédou who may have triggered the spread to Macenta and other nearby prefectures in February 2014.

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