title: Characterizing risk of Ebola transmission based on frequency and type of case-contact exposures.
abstract: During the initial months of the 2013-2016 Ebola epidemic, rapid geographical dissemination and intense transmission challenged response efforts across West Africa. Contextual behaviours associated with increased risk of exposure included travel to high-transmission settings, caring for sick and preparing the deceased for traditional funerals. Although such behaviours are widespread in West Africa, high-transmission pockets were observed. Superspreading and clustering are typical phenomena in infectious disease outbreaks, as a relatively small number of transmission chains are often responsible for the majority of events. Determining the characteristics of contacts at greatest risk of developing disease and of cases with greatest transmission potential could therefore help curb propagation of infection. Our analysis of contact tracing data from Montserrado County, Liberia, suggested that the probability of transmission was 4.5 times higher for individuals who were reported as having contact with multiple cases. The probability of individuals developing disease was not significantly associated with age or sex of their source case but was higher when they were in the same household as the infectious case. Surveillance efforts for rapidly identifying symptomatic individuals and effectively messaged campaigns encouraging household members to bring the sick to designated treatment centres without administration of home care could mitigate transmission.This article is part of the themed issue 'The 2013-2016 West African Ebola epidemic: data, decision-making and disease control'.
authors.affiliation: Center for Infectious Disease Modeling and Analysis, Yale School of Public Health, New Haven, CT 06510, USA laura.skrip@yale.edu.
authors.forename: Laura A
authors.identifier: http://orcid.org/0000-0002-7952-0660
authors.initials: LA
authors.lastname: Skrip
authors.affiliation: Ministry of Health, Congo Town, Tubman Blvd, Monrovia, Liberia.|A.M. Dogliotti College of Medicine, University of Liberia, Tubman Blvd, Monrovia, Liberia.|National Institute of Allergy and Infectious Diseases, PREVAIL-III Study, JFK Hospital, Tubman Blvd, Monrovia, Liberia.
authors.forename: Mosoka P
authors.initials: MP
authors.lastname: Fallah
authors.affiliation: Department of Biostatistics, Yale School of Public Health, New Haven, CT 06510, USA.
authors.forename: Stephen G
authors.initials: SG
authors.lastname: Gaffney
authors.affiliation: Biostatistics Unit, The Gertner Institute for Epidemiology and Health Policy Research, Ramat Gan 52621, Israel.
authors.forename: Rami
authors.initials: R
authors.lastname: Yaari
authors.affiliation: Department of Industrial Engineering, Tel Aviv University, Tel Aviv 6997801, Israel.
authors.forename: Dan
authors.initials: D
authors.lastname: Yamin
authors.affiliation: Biostatistics Unit, The Gertner Institute for Epidemiology and Health Policy Research, Ramat Gan 52621, Israel.|Department of Epidemiology and Preventive Medicine, The Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv 6997801, Israel.
authors.forename: Amit
authors.initials: A
authors.lastname: Huppert
authors.affiliation: Ministry of Health, Congo Town, Tubman Blvd, Monrovia, Liberia.
authors.forename: Luke
authors.initials: L
authors.lastname: Bawo
authors.affiliation: Ministry of Health, Congo Town, Tubman Blvd, Monrovia, Liberia.
authors.forename: Tolbert
authors.initials: T
authors.lastname: Nyenswah
authors.affiliation: Center for Infectious Disease Modeling and Analysis, Yale School of Public Health, New Haven, CT 06510, USA.|A.M. Dogliotti College of Medicine, University of Liberia, Tubman Blvd, Monrovia, Liberia.
authors.forename: Alison P
authors.initials: AP
authors.lastname: Galvani
mesh_terms: D016358:Contact Tracing; D019142:Hemorrhagic Fever, Ebola / Q000635:transmission* / Q000821:virology; D006801:Humans; D007988:Liberia; D008962:Models, Theoretical; D012306:Risk
keywords: Ebola virus disease; West Africa; contact tracing; infectious disease transmission; targeted intervention