title: Heterogeneities in the case fatality ratio in the West African Ebola outbreak 2013-2016.
abstract: The 2013-2016 Ebola outbreak in West Africa is the largest on record with 28 616 confirmed, probable and suspected cases and 11 310 deaths officially recorded by 10 June 2016, the true burden probably considerably higher. The case fatality ratio (CFR: proportion of cases that are fatal) is a key indicator of disease severity useful for gauging the appropriate public health response and for evaluating treatment benefits, if estimated accurately. We analysed individual-level clinical outcome data from Guinea, Liberia and Sierra Leone officially reported to the World Health Organization. The overall mean CFR was 62.9% (95% CI: 61.9% to 64.0%) among confirmed cases with recorded clinical outcomes. Age was the most important modifier of survival probabilities, but country, stage of the epidemic and whether patients were hospitalized also played roles. We developed a statistical analysis to detect outliers in CFR between districts of residence and treatment centres (TCs), adjusting for known factors influencing survival and identified eight districts and three TCs with a CFR significantly different from the average. From the current dataset, we cannot determine whether the observed variation in CFR seen by district or treatment centre reflects real differences in survival, related to the quality of care or other factors or was caused by differences in reporting practices or case ascertainment.This article is part of the themed issue 'The 2013-2016 West African Ebola epidemic: data, decision-making and disease control'.
authors.affiliation: MRC Centre for Outbreak Analysis and Modelling, Department of Infectious Disease Epidemiology, Imperial College London, London W2 1PG, UK.
authors.forename: Tini
authors.identifier: http://orcid.org/0000-0002-8952-4710
authors.initials: T
authors.lastname: Garske
authors.affiliation: MRC Centre for Outbreak Analysis and Modelling, Department of Infectious Disease Epidemiology, Imperial College London, London W2 1PG, UK.
authors.forename: Anne
authors.identifier: http://orcid.org/0000-0002-8443-9162
authors.initials: A
authors.lastname: Cori
authors.affiliation: WHO, 1211 Geneva, Switzerland.
authors.forename: Archchun
authors.initials: A
authors.lastname: Ariyarajah
authors.affiliation: MRC Centre for Outbreak Analysis and Modelling, Department of Infectious Disease Epidemiology, Imperial College London, London W2 1PG, UK.
authors.forename: Isobel M
authors.initials: IM
authors.lastname: Blake
authors.affiliation: MRC Centre for Outbreak Analysis and Modelling, Department of Infectious Disease Epidemiology, Imperial College London, London W2 1PG, UK.
authors.forename: Ilaria
authors.initials: I
authors.lastname: Dorigatti
authors.affiliation: WHO, 1211 Geneva, Switzerland.|Robert Koch Institute, 13302 Berlin, Germany.
authors.forename: Tim
authors.initials: T
authors.lastname: Eckmanns
authors.affiliation: MRC Centre for Outbreak Analysis and Modelling, Department of Infectious Disease Epidemiology, Imperial College London, London W2 1PG, UK.|Big Data Institute, University of Oxford, Oxford OX3 7LF, UK.
authors.forename: Christophe
authors.initials: C
authors.lastname: Fraser
authors.affiliation: MRC Centre for Outbreak Analysis and Modelling, Department of Infectious Disease Epidemiology, Imperial College London, London W2 1PG, UK.
authors.forename: Wes
authors.initials: W
authors.lastname: Hinsley
authors.affiliation: MRC Centre for Outbreak Analysis and Modelling, Department of Infectious Disease Epidemiology, Imperial College London, London W2 1PG, UK.
authors.forename: Thibaut
authors.initials: T
authors.lastname: Jombart
authors.affiliation: MRC Integrative Epidemiology Unit, University of Bristol, Bristol BS8 2BN, UK.
authors.forename: Harriet L
authors.initials: HL
authors.lastname: Mills
authors.affiliation: MRC Centre for Outbreak Analysis and Modelling, Department of Infectious Disease Epidemiology, Imperial College London, London W2 1PG, UK.
authors.forename: Gemma
authors.identifier: http://orcid.org/0000-0001-5723-5028
authors.initials: G
authors.lastname: Nedjati-Gilani
authors.affiliation: WHO, 1211 Geneva, Switzerland.
authors.forename: Emily
authors.initials: E
authors.lastname: Newton
authors.affiliation: MRC Centre for Outbreak Analysis and Modelling, Department of Infectious Disease Epidemiology, Imperial College London, London W2 1PG, UK.
authors.forename: Pierre
authors.initials: P
authors.lastname: Nouvellet
authors.affiliation: WHO, 1211 Geneva, Switzerland.
authors.forename: Devin
authors.initials: D
authors.lastname: Perkins
authors.affiliation: MRC Centre for Outbreak Analysis and Modelling, Department of Infectious Disease Epidemiology, Imperial College London, London W2 1PG, UK.
authors.forename: Steven
authors.initials: S
authors.lastname: Riley
authors.affiliation: WHO, 1211 Geneva, Switzerland.
authors.forename: Dirk
authors.initials: D
authors.lastname: Schumacher
authors.affiliation: WHO, 1211 Geneva, Switzerland.
authors.forename: Anita
authors.initials: A
authors.lastname: Shah
authors.affiliation: MRC Centre for Outbreak Analysis and Modelling, Department of Infectious Disease Epidemiology, Imperial College London, London W2 1PG, UK.|Center for Global Health Research and Education, Institut Pasteur, Paris 75015, France.
authors.forename: Maria D
authors.initials: MD
authors.lastname: Van Kerkhove
authors.affiliation: WHO, 1211 Geneva, Switzerland.
authors.forename: Christopher
authors.initials: C
authors.lastname: Dye
authors.affiliation: MRC Centre for Outbreak Analysis and Modelling, Department of Infectious Disease Epidemiology, Imperial College London, London W2 1PG, UK.
authors.forename: Neil M
authors.initials: NM
authors.lastname: Ferguson
authors.affiliation: MRC Centre for Outbreak Analysis and Modelling, Department of Infectious Disease Epidemiology, Imperial College London, London W2 1PG, UK c.donnelly@imperial.ac.uk.
authors.forename: Christl A
authors.identifier: http://orcid.org/0000-0002-0195-2463
authors.initials: CA
authors.lastname: Donnelly
mesh_terms: D058872:Epidemics / Q000706:statistics & numerical data*; D016701:Guinea / Q000453:epidemiology; D019142:Hemorrhagic Fever, Ebola / Q000453:epidemiology* / Q000401:mortality; D006801:Humans; D007988:Liberia / Q000453:epidemiology; D009026:Mortality; D011634:Public Health / Q000706:statistics & numerical data; D012807:Sierra Leone / Q000453:epidemiology; D014944:World Health Organization
keywords: Ebola virus disease; case fatality ratio; mortality; outlier detection; severity; spatial heterogeneity