Epidemiology of Ebola Virus Disease in the Western Area Region of Sierra Leone, 2014–2015

Margaret Lamunu, Olushayo Oluseun Olu, James Bangura, Zabulon Yoti, Thomas Takpau Samba, David Kabba Kargbo, Foday Mohamed Dafae, Muhammad Ali Raja, Noah Sempira, Michael Lyazi Ivan, Aarti Sing, Fredson Kurti-George, Negusu Worku, Pamela Mitula, Louisa Ganda, Robert Samupindi, Roland Conteh, Kande-Bure Kamara, Beatrice Muraguri, Michael Kposowa, Joseph Charles, Malimbo Mugaga, Christopher Dye, Anshu Banerjee, Pierre Formenty, Brima Kargbo, Raymond Bruce Aylward

Western Area (WA) of Sierra Leone including the capital, Freetown, experienced an unprecedented outbreak of Ebola from 2014 to 2015. At the onset of the epidemic, there was little information about the epidemiology, transmission dynamics, and risk factors in urban settings as previous outbreaks were limited to rural/semi-rural settings. This study, therefore, aimed to describe the epidemiology of the outbreak and the factors which had most impact on the transmission of the epidemic and whether there were different drivers from those previously described in rural settings. We conducted a descriptive epidemiology study in WA, Sierra Leone using secondary data from the National Ebola outbreak database. We also reviewed the Ebola situation reports, response strategy documents, and other useful documents. A total of 4,955 Ebola cases were identified between June 2014 and November 2015, although there were reports of cases occurring in WA toward end of May. All wards were affected, and Waterloo Area I (Ward 330), the capital city of Western Area Rural District, recorded the highest numbers of cases (580) and deaths (236). Majority of cases (63.4%) and deaths (66.8%) were in WA Urban District (WAU); 44 cases were imported from other provinces. Only 20% of cases had a history of contact with an Ebola case, and more than 30% were death alerts. Equal numbers of males and females were infected, and very few cases (3.2%) were health workers. Overall, transmission was through contact with infected individuals, and intense transmission occurred at the community level. In WAU, transmission was mostly between neighbors and among inhabitants of shared accommodations. The drivers of transmission included high population movement to and from WA, overcrowding, fear and lack of trust in the response, and negative community behaviors. Transmission was mostly through contact and with limited transmission through sex and breast milk. The unprecedented outbreak in WA was attributed to delayed detection, inadequate preparedness and response, intense population movements, overcrowding, and unresponsive communities. Anticipation, strengthening preparedness for early detection, and swift and effective response remains critical in mitigating a potential urban explosion of similar future outbreaks.