Abstract
BackgroundFor the 2013–2016 Ebola epidemic in West Africa, the largest Ebola virus disease (EVD) epidemic to date, we aim to analyse the patient mix in detail to characterise key sources of spatiotemporal heterogeneity in the case fatality ratios (CFR). MethodsWe applied a non-parametric Boosted Regression Trees (BRT) imputation approach for patients with missing survival outcomes and adjusted for model imperfection. Semivariogram analysis and kriging were used to investigate spatiotemporal heterogeneities. ResultsCFR estimates varied significantly between districts and over time over the course of the epidemic. BRT modelling accounted for most of the spatiotemporal variation and interactions in CFR, but moderate spatial autocorrelation remained for distances up to approximately 90 km. Combining district-level CFR estimates and kriged district-level residuals provided the best linear unbiased predicted map of CFR accounting for the both explained and unexplained spatial variation. Temporal autocorrelation was not observed in the district-level residuals from the BRT estimates. ConclusionsThis study provides new insight into the epidemiology of the 2013–2016 West African Ebola epidemic with a view of informing future public health contingency planning, resource allocation and impact assessment. The analytical framework developed in this analysis, coupled with key domain knowledge, could be deployed in real time to support the response to ongoing and future outbreaks.
Highlights
Ebola virus disease (EVD) is associated with a very high fatality, with 10,884 deaths reported for the West African epidemic (Qin et al, 2015, Van Kerkhove et al, 2015)
Robust case fatality ratios (CFR) estimates for entire epidemics and subgroups inform the situational awareness during ongoing outbreaks, but are essential for future public health contingency planning, resource allocation and for evaluating the impact of interventions subsequently implemented during outbreaks (Garske et al, 2017)
In Sierra Leone, the predicted CFR adjusted for imputation was highest in a few districts from Freetown in the West Urban area to Kono to the east of the country, and the predicted CFR adjusted for imputation was lowest in Kailahun
Summary
Ebola virus disease (EVD) is associated with a very high fatality, with 10,884 deaths (among 26,277 cases) reported for the West African epidemic (Qin et al, 2015, Van Kerkhove et al, 2015). A strong case has been made that simple spatiotemporal characterisations of such heterogeneities available in real time could have enhanced the national and global response as the West African epidemic unfolded (Koch, 2015). For the 2013–2016 Ebola epidemic in West Africa, the largest Ebola virus disease (EVD) epidemic to date, we aim to analyse the patient mix in detail to characterise key sources of spatiotemporal heterogeneity in the case fatality ratios (CFR). Conclusions: This study provides new insight into the epidemiology of the 2013–2016 West African Ebola epidemic with a view of informing future public health contingency planning, resource allocation and impact assessment.
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