title: Assessment of the potential for international dissemination of Ebola virus via commercial air travel during the 2014 west African outbreak.
abstract: BACKGROUND
  The WHO declared the 2014 west African Ebola epidemic a public health emergency of international concern in view of its potential for further international spread. Decision makers worldwide are in need of empirical data to inform and implement emergency response measures. Our aim was to assess the potential for Ebola virus to spread across international borders via commercial air travel and assess the relative efficiency of exit versus entry screening of travellers at commercial airports.
  
  
  METHODS
  We analysed International Air Transport Association data for worldwide flight schedules between Sept 1, 2014, and Dec 31, 2014, and historic traveller flight itinerary data from 2013 to describe expected global population movements via commercial air travel out of Guinea, Liberia, and Sierra Leone. Coupled with Ebola virus surveillance data, we modelled the expected number of internationally exported Ebola virus infections, the potential effect of air travel restrictions, and the efficiency of airport-based traveller screening at international ports of entry and exit. We deemed individuals initiating travel from any domestic or international airport within these three countries to have possible exposure to Ebola virus. We deemed all other travellers to have no significant risk of exposure to Ebola virus.
  
  
  RESULTS
  Based on epidemic conditions and international flight restrictions to and from Guinea, Liberia, and Sierra Leone as of Sept 1, 2014 (reductions in passenger seats by 51% for Liberia, 66% for Guinea, and 85% for Sierra Leone), our model projects 2.8 travellers infected with Ebola virus departing the above three countries via commercial flights, on average, every month. 91,547 (64%) of all air travellers departing Guinea, Liberia, and Sierra Leone had expected destinations in low-income and lower-middle-income countries. Screening international travellers departing three airports would enable health assessments of all travellers at highest risk of exposure to Ebola virus infection.
  
  
  CONCLUSIONS
  Decision makers must carefully balance the potential harms from travel restrictions imposed on countries that have Ebola virus activity against any potential reductions in risk from Ebola virus importations. Exit screening of travellers at airports in Guinea, Liberia, and Sierra Leone would be the most efficient frontier at which to assess the health status of travellers at risk of Ebola virus exposure, however, this intervention might require international support to implement effectively.
  
  
  BACKGROUND
  Canadian Institutes of Health Research.
authors.affiliation: Department of Medicine, Division of Infectious Diseases, University of Toronto, Toronto, ON, Canada; Divisions of Internal Medicine and Infectious Diseases, University Health Network, Toronto, ON, Canada.
authors.forename: Isaac I
authors.initials: II
authors.lastname: Bogoch
authors.affiliation: Centre for Research on Inner City Health, Li Ka Shing Knowledge Institute, St Michael's Hospital, Toronto, ON, Canada.
authors.forename: Maria I
authors.initials: MI
authors.lastname: Creatore
authors.affiliation: Division of Global Migration and Quarantine, Centers for Disease Control and Prevention, Atlanta, GA, USA.
authors.forename: Martin S
authors.initials: MS
authors.lastname: Cetron
authors.affiliation: Center for Biomedical Informatics, Harvard Medical School, Boston, MA, USA; Children's Hospital Informatics Program, Boston Children's Hospital Boston, MA, USA.
authors.forename: John S
authors.initials: JS
authors.lastname: Brownstein
authors.affiliation: Quarantine and Border Health Services Branch, Division of Global Migration and Quarantine, Centers for Disease Control and Prevention, Atlanta, GA, USA.
authors.forename: Nicki
authors.initials: N
authors.lastname: Pesik
authors.affiliation: Centre for Research on Inner City Health, Li Ka Shing Knowledge Institute, St Michael's Hospital, Toronto, ON, Canada.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Miniota
authors.affiliation: Health Security Infrastructure Branch, Public Health Agency of Canada, Ottawa, ON, Canada.
authors.forename: Theresa
authors.initials: T
authors.lastname: Tam
authors.affiliation: Centre for Research on Inner City Health, Li Ka Shing Knowledge Institute, St Michael's Hospital, Toronto, ON, Canada.
authors.forename: Wei
authors.initials: W
authors.lastname: Hu
authors.affiliation: Centre for Research on Inner City Health, Li Ka Shing Knowledge Institute, St Michael's Hospital, Toronto, ON, Canada.
authors.forename: Adriano
authors.initials: A
authors.lastname: Nicolucci
authors.affiliation: Schulich School of Medicine & Dentistry, University of Western Ontario, London, ON, Canada.
authors.forename: Saad
authors.initials: S
authors.lastname: Ahmed
authors.affiliation: Centre for Research on Inner City Health, Li Ka Shing Knowledge Institute, St Michael's Hospital, Toronto, ON, Canada.
authors.forename: James W
authors.initials: JW
authors.lastname: Yoon
authors.affiliation: Centre for Research on Inner City Health, Li Ka Shing Knowledge Institute, St Michael's Hospital, Toronto, ON, Canada.
authors.forename: Isha
authors.initials: I
authors.lastname: Berry
authors.affiliation: Fogarty International Center, National Institutes of Health, Bethesda, MD, USA; Spatial Ecology and Epidemiology Group, Department of Zoology, University of Oxford, Oxford, UK.
authors.forename: Simon I
authors.initials: SI
authors.lastname: Hay
authors.affiliation: Children's Hospital Informatics Program, Boston Children's Hospital Boston, MA, USA; Department of Medicine, Faculty of Medicine, University of British Columbia, Vancouver, BC, Canada.
authors.forename: Aranka
authors.initials: A
authors.lastname: Anema
authors.affiliation: Fogarty International Center, National Institutes of Health, Bethesda, MD, USA; Department of Geography and Environment, University of Southampton, Southampton, UK; Flowminder Foundation, Stockholm, Sweden.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Tatem
authors.affiliation: Department of Medicine, Division of Infectious Diseases, University of Toronto, Toronto, ON, Canada.
authors.forename: Derek
authors.initials: D
authors.lastname: MacFadden
authors.affiliation: Centre for Research on Inner City Health, Li Ka Shing Knowledge Institute, St Michael's Hospital, Toronto, ON, Canada.
authors.forename: Matthew
authors.initials: M
authors.lastname: German
authors.affiliation: Department of Medicine, Division of Infectious Diseases, University of Toronto, Toronto, ON, Canada; Centre for Research on Inner City Health, Li Ka Shing Knowledge Institute, St Michael's Hospital, Toronto, ON, Canada. Electronic address: khank@smh.ca.
authors.forename: Kamran
authors.initials: K
authors.lastname: Khan
mesh_terms: D064870:Air Travel / Q000706:statistics & numerical data*; D004196:Disease Outbreaks; D029043:Ebolavirus / Q000472:pathogenicity*; D016701:Guinea / Q000453:epidemiology; D019142:Hemorrhagic Fever, Ebola / Q000453:epidemiology* / Q000635:transmission; D006801:Humans; D007988:Liberia / Q000453:epidemiology; D008403:Mass Screening / Q000592:standards*; D015233:Models, Statistical; D011634:Public Health; D012307:Risk Factors; D012807:Sierra Leone / Q000453:epidemiology