Early transmission dynamics of Ebola virus disease (EVD) in Sierra Leone and Liberia, 2014. a) The cumulative number of confirmed and probable cases of EVD as a function of calendar time . Filled circles represent cases in Liberia, while unfilled triangles represent cases in Sierra Leone. The solid line shows the exponential growth fit to the incidence curve in Liberia. The dashed line is the exponential fit to the early phase in Sierra Leone (up to 8 July 2014), while the dotted line shows the exponential fit to the later phase in the same country. b) The relationship between the exponential growth rate and the corresponding reproduction number for EVD based on a Weibull distributed generation time with shape and scale parameters of 2.59 and 13.60, respectively. Arrows indicate the uncertainty range (95% confidence interval) of the exponential growth rate estimated from the corresponding epidemic data.