Ebola Virus Disease in West Africa — The First 9 Months of the Epidemic and Forward Projections

Bruce Aylward, Philippe Barboza, Luke Bawo, Eric Bertherat, Pepe Bilivogui, Isobel Blake, Rick Brennan, Sylvie Briand, Jethro Magwati Chakauya, Kennedy Chitala, Roland M Conteh, Anne Cori, Alice Croisier, Jean-Marie Dangou, Boubacar Diallo, Christl A Donnelly, Christopher Dye, Tim Eckmanns, Neil M Ferguson, Pierre Formenty, Caroline Fuhrer, Keiji Fukuda, Tini Garske, Alex Gasasira, Stephen Gbanyan, Peter Graaff, Emmanuel Heleze, Amara Jambai, Thibaut Jombart, Francis Kasolo, Albert Mbule Kadiobo, Sakoba Keita, Daniel Kertesz, Moussa Koné, Chris Lane, Jered Markoff, Moses Massaquoi, Harriet Mills, John Mike Mulba, Emmanuel Musa, Joel Myhre, Abdusalam Nasidi, Eric Nilles, Pierre Nouvellet, Deo Nshimirimana, Isabelle Nuttall, Tolbert Nyenswah, Olushayo Olu, Scott Pendergast, William Perea, Jonathan Polonsky, Steven Riley, Olivier Ronveaux, Keita Sakoba, Ravi Santhana Gopala Krishnan, Mikiko Senga, Faisal Shuaib, Maria D Van Kerkhove, Rui Vaz, Niluka Wijekoon Kannangarage, Zabulon Yoti

Background On March 23, 2014, the World Health Organization (WHO) was notified of an outbreak of Ebola virus disease (EVD) in Guinea. On August 8, the WHO declared the epidemic to be a "public health emergency of international concern." Methods By September 14, 2014, a total of 4507 probable and confirmed cases, including 2296 deaths from EVD (Zaire species) had been reported from five countries in West Africa - Guinea, Liberia, Nigeria, Senegal, and Sierra Leone. We analyzed a detailed subset of data on 3343 confirmed and 667 probable Ebola cases collected in Guinea, Liberia, Nigeria, and Sierra Leone as of September 14. Results The majority of patients are 15 to 44 years of age (49.9% male), and we estimate that the case fatality rate is 70.8% (95% confidence interval [CI], 69 to 73) among persons with known clinical outcome of infection. The course of infection, including signs and symptoms, incubation period (11.4 days), and serial interval (15.3 days), is similar to that reported in previous outbreaks of EVD. On the basis of the initial periods of exponential growth, the estimated basic reproduction numbers (R0 ) are 1.71 (95% CI, 1.44 to 2.01) for Guinea, 1.83 (95% CI, 1.72 to 1.94) for Liberia, and 2.02 (95% CI, 1.79 to 2.26) for Sierra Leone. The estimated current reproduction numbers (R) are 1.81 (95% CI, 1.60 to 2.03) for Guinea, 1.51 (95% CI, 1.41 to 1.60) for Liberia, and 1.38 (95% CI, 1.27 to 1.51) for Sierra Leone; the corresponding doubling times are 15.7 days (95% CI, 12.9 to 20.3) for Guinea, 23.6 days (95% CI, 20.2 to 28.2) for Liberia, and 30.2 days (95% CI, 23.6 to 42.3) for Sierra Leone. Assuming no change in the control measures for this epidemic, by November 2, 2014, the cumulative reported numbers of confirmed and probable cases are predicted to be 5740 in Guinea, 9890 in Liberia, and 5000 in Sierra Leone, exceeding 20,000 in total. Conclusions These data indicate that without drastic improvements in control measures, the numbers of cases of and deaths from EVD are expected to continue increasing from hundreds to thousands per week in the coming months.