Real-Time Assessment of the International Spreading Risk Associated with the 2014 West African Ebola Outbreak

A. Pastore y Piontti, Q. Zhang, M. F. C. Gomes, L. Rossi, C. Poletto, V. Colizza, D.L. Chao, I. Longing, M.E. Halloran and A. Vespignani.
Mathematical and Statistical Modeling for Emerging and Re-emerging Infectious Diseases
Springer, G. Chowell and J.M. Hyman (eds), pp 39-56 (2016)
July 28, 2016


Background: The  2014 West African Ebola Outbreak is so far the largest and deadliest recorded  in history. The affected countries, Sierra Leone, Guinea, Liberia, and  Nigeria, have been struggling to contain and to mitigate the outbreak. The  ongoing rise in confirmed and suspected cases, 2615 as of 20 August 2014, is  considered to increase the risk of international dissemination, especially  because the epidemic is now affecting cities with major commercial airports.  Method: We use the Global Epidemic and Mobility Model to generate stochastic,  individual based simulations of epidemic spread worldwide, yielding, among  other measures, the incidence and seeding events at a daily resolution for  3,362 subpopulations in 220 countries. The mobility model integrates daily  airline passenger traffic worldwide and the disease model includes the  community, hospital, and burial transmission dynamic. We use a multimodel  inference approach calibrated on data from 6 July to the date of 9 August  2014. The estimates obtained were used to generate a 3-month ensemble  forecast that provides quantitative estimates of the local transmission of  Ebola virus disease in West Africa and the probability of international  spread if the containment measures are not successful at curtailing the  outbreak. Results: We model the short-term growth rate of the disease in the  affected West African countries and estimate the basic reproductive number to  be in the range 1.5 − 2.0 (interval at the 1/10 relative likelihood). We  simulated the international spreading of the outbreak and provide the  estimate for the probability of Ebola virus disease case importation in  countries across the world. Results indicate that the short-term (3 and 6  weeks) probability of international spread outside the African region is  small, but not negligible. The extension of the outbreak is more likely  occurring in African countries, increasing the risk of international  dissemination on a longer time scale.

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