Measuring the impact of Ebola control measures in Sierra Leone

Abstract

Between September 2014 and February 2015, the number of Ebola virus disease (EVD) cases reported in Sierra Leone declined in many districts. During this period, a major international response was put in place, with thousands of treatment beds introduced alongside other infection control measures. However, assessing the impact of the response is challenging, as several factors could have influenced the decline in infections, including behavior changes and other community interventions. We developed a mathematical model of EVD transmission, and measured how transmission changed over time in the 12 districts of Sierra Leone with sustained transmission between June 2014 and February 2015. We used the model to estimate how many cases were averted as a result of the introduction of additional treatment beds in each area. Examining epidemic dynamics at the district level, we estimated that 56,600 (95% credible interval: 48,300–84,500) Ebola cases (both reported and unreported) were averted in Sierra Leone up to February 2, 2015 as a direct result of additional treatment beds being introduced. We also found that if beds had been introduced 1 month earlier, a further 12,500 cases could have been averted. Our results suggest the unprecedented local and international response led to a substantial decline in EVD transmission during 2014–2015. In particular, the introduction of beds had a direct impact on reducing EVD cases in Sierra Leone, although the effect varied considerably between districts.

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

“…Due to the lack of data about the implementation of interventions in individual chiefdoms, we were unable to differentiate the effects of each kind of intervention. The number of beds in healthcare facilities has been used as a surrogate for the intervention intensity (18). The number of beds was closely related to, but may not fully capture, the overall intervention intensity.…”

“…Our findings have deepened the understanding of the transmission dynamics of EVD and provided key information for future modeling efforts in forecasting future epidemics and establishing intervention strategies. studies have attempted to capture the spatial component in the epidemic data (18,19). In addition, efforts to quantify the transmissibility of EVD in households, an important transmission venue for many contagious diseases, have been hindered by lack of data.…”

“…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.…”

After Ebola in West Africa — Unpredictable Risks, Preventable Epidemics

“…Mathematical modeling [19][20][21][22] has been used to investigate what reduction in transmission, achieved by what means, would have been necessary to explain the epidemics in Guinea, Liberia, and Sierra Leone. All these modeling analyses show, as expected, that admitting patients to Ebola treatment centers and shortening the delay before hospitalization could have played a large part in slowing the increase and accelerating the decline in case incidence.…”

“…In line with the differing rates of decline in incidence, bed capacity was scaled up first in Liberia, then in Sierra Leone, and eventually in Guinea (see the Supplementary Appendix). 22 Empirical evidence of the effect of rapid patient isolation and hospitalization comes from investigations of a series of small outbreaks in Liberia. [23][24][25][26][27] Twelve outbreaks were included in a study of the Rapid Isolation and Treatment of Ebola (RITE) strategy, applied between July and November 2014.…”