Abstract
The Ebola epidemic in West Africa 2013-2015 was the largest ever observed and almost 30,000 persons were infected. Mathematical modelling studies showed considerable variation in the epidemic growth between the three hardest-hit countries Guinea, Liberia and Sierra Leone. Moreover, case numbers differed substantially at subnational level. These observations suggested that the risk of infection and the magnitude of transmission differed not only between but also within the affected countries. These circumstances prompted me to investigate the spatial distribution, the incidence and the transmissibility of Ebola in Guinea, Liberia and Sierra Leone at a district-level. For this purpose, I implemented a mixed effects model to estimate local initial transmission as measured by R0. The mixed model approach yielded plausible estimates and confirmed the notion of spatial heterogeneity. This finding raised some questions about drivers of disease transmission at a population level. Thus in a second step, I used an ecological study design to identify demographic risk factors associated with an increased spread of Ebola. Specifically, I quantified the velocity of the epidemic wave and risk factors associated with geographical spread from the origin as well as risk factors for local transmission using various regression models. The analysis showed that large-scale and small-scale crowding may have played an important role during this epidemic and that these factors may have facilitated the spread of Ebola.
Fabienne Krauer, MSc
Institute of Social and Preventive Medicine (ISPM), University of Bern, Switzerland