Incubation periods impact the spatial predictability of cholera and Ebola outbreaks in Sierra Leone

Understanding how infectious diseases spread is critical for preventing and containing outbreaks. While advances have been made in forecasting epidemics, much is still unknown. Here we show that the incubation period, the time between exposure to a pathogen and onset of symptoms, is an important factor in predicting spatiotemporal spread of disease and provides one explanation for the different trajectories of recent Ebola and cholera outbreaks in Sierra Leone. We find that outbreaks of pathogens with longer incubation periods, such as Ebola, tend to have less predictable spread, whereas pathogens with shorter incubation periods, such as cholera, spread in a more predictable, wavelike pattern. These findings have implications for the scale and timing of reactive interventions, such as vaccination campaigns.