Determinants of Transmission Risk during the Late Stage of the West African Ebola Epidemic

Alexis Robert, William Edmunds, Conall H. Watson, Ana Maria Henao-Restrepo, Pierre Stéphane Gsell, Elizabeth Williamson, Ira M. Longini, Keïta Sakoba, Adam J. Kucharski, Alhassane Touré, Sévérine Danmadji Nadlaou, Boubacar Diallo, Mamamdou Saidou Barry, Thierno Oumar Fofana, Louceny Camara, Ibrahima Lansana Kaba, Lansana Sylla, Mohamed Lamine Diaby, Ousmane Soumah, Abdourahime DialloAmadou Niare, Abdourahmane Diallo, Rosalind M. Eggo

Research output: Contribution to journalArticlepeer-review


Understanding risk factors for Ebola transmission is key for effective prediction and design of interventions. We used data on 860 cases in 129 chains of transmission from the latter half of the 2013-2016 Ebola epidemic in Guinea. Using negative binomial regression, we determined characteristics associated with the number of secondary cases resulting from each infected individual. We found that attending an Ebola treatment unit was associated with a 38% decrease in secondary cases (incidence rate ratio (IRR) = 0.62, 95% confidence interval (CI): 0.38, 0.99) among individuals that did not survive. Unsafe burial was associated with a higher number of secondary cases (IRR = 1.82, 95% CI: 1.10, 3.02). The average number of secondary cases was higher for the first generation of a transmission chain (mean = 1.77) compared with subsequent generations (mean = 0.70). Children were least likely to transmit (IRR = 0.35, 95% CI: 0.21, 0.57) compared with adults, whereas older adults were associated with higher numbers of secondary cases. Men were less likely to transmit than women (IRR = 0.71, 95% CI: 0.55, 0.93). This detailed surveillance data set provided an invaluable insight into transmission routes and risks. Our analysis highlights the key role that age, receiving treatment, and safe burial played in the spread of EVD.

Original languageEnglish
Pages (from-to)1319-1327
Number of pages9
JournalAmerican Journal of Epidemiology
Issue number7
Publication statusPublished - 1 Jul 2019
Externally publishedYes


  • Ebola
  • Guinea
  • multiple imputation
  • regression analysis
  • risk factors


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