Estimating the basic reproductive ratio for the Ebola outbreak in Liberia and Sierra Leone

Abstract

BackgroundEbola virus disease has reemerged as a major public health crisis in Africa, with isolated cases also observed globally, during the current outbreak.MethodsTo estimate the basic reproductive ratio R0, which is a measure of the severity of the outbreak, we developed a SEIR (susceptible-exposed-infected-recovered) type deterministic model, and used data from the Centers for Disease Control and Prevention (CDC), for the Ebola outbreak in Liberia and Sierra Leone. Two different data sets are available: one with raw reported data and one with corrected data (as the CDC suspects under-reporting).ResultsUsing a deterministic ordinary differential equation transmission model for Ebola epidemic, the basic reproductive ratio R0 for Liberia resulted to be 1.757 and 1.9 for corrected and uncorrected case data, respectively. For Sierra Leone, R0 resulted to be 1.492 and 1.362 for corrected and uncorrected case data, respectively. In each of the two cases we considered, the estimate for the basic reproductive ratio was initially greater than unity leading to an epidemic outbreak.ConclusionWe obtained robust estimates for the value of R0 associated with the 2014 Ebola outbreak, and showed that there is close agreement between our estimates of R0. Analysis of our model also showed that effective isolation is required, with the contact rate in isolation less than one quarter of that for the infected non-isolated population, and that the fraction of high-risk individuals must be brought to less than 10% of the overall susceptible population, in order to bring the value of R0 to less than 1, and hence control the outbreak.Electronic supplementary materialThe online version of this article (doi:10.1186/s40249-015-0043-3) contains supplementary material, which is available to authorized users.

Spatiotemporal Transmission Dynamics of Recent Ebola Outbreak in Sierra Leone, West Africa: Impact of Control Measures

“…Furthermore, for the given parameter value in Table 3, the value of R 0 for the 2014 Ebola outbreak in Sierra Leone is R 0 = 1.64277. Although this estimate is lower than that reported by Althaus 11 and slightly greater than Khan et al, 32 it fits well with the recent outbreak scenario in Sierra Leone.…”

Transmission dynamics of Ebola virus disease and intervention effectiveness in Sierra Leone

“…The growing concern over the repeated emergence of EVD (7,8) has stimulated many studies on these outbreaks, in particular on the most recent one in West Africa, trying to understand the transmission mechanisms and the effectiveness of containment strategies (9)(10)(11)(12)(13)(14)(15)(16)(17)(18). These studies, however, either used limited data at an early stage of the epidemic or assessed a single influential factor.…”

Heterogeneity in District-Level Transmission of Ebola Virus Disease during the 2013-2015 Epidemic in West Africa

“…At national level, our approach was not comparable to results of other methods. Several mechanistic [6,10,14,[16][17][18][19][50][51][52] and phenomenological [15,34,53] The ecological analysis showed associations between R 0 and population-level factors linked to urbanisation and crowding. Analysis at the population-level is appropriate when the mechanism of action involves interactions between individuals, for example the potential for spread of an infection in densely populated areas [54].…”

“…A common approach to the estimation of R 0 consists of fitting mathematical transmission models to observed outbreak data. In the West African EVD epidemic, several mathematical modelling studies have described the variation in R 0 between [6,10,[14][15][16][17][18][19] and within [20][21][22][23][24][25] the three countries. Most studies found estimates of R 0 ranging between 1.5 and 2.5, agreeing with results from models of earlier outbreaks ranging from 1.4-4.7 (summarised in [26]).…”