Decreased Ebola Transmission after Rapid Response to Outbreaks in Remote Areas, Liberia, 2014

Abstract

We measured the reproduction number before and after interventions were implemented to reduce Ebola transmission in 9 outbreaks in Liberia during 2014. We evaluated risk factors for secondary cases and the association between patient admission to an Ebola treatment unit (ETU) and survival. The reproduction number declined 94% from 1.7 (95% CI 1.1-2.6) to 0.1 (95% CI 0.02-0.6) after interventions began. The risk for secondary infections was 90% lower for patients admitted to an ETU (risk ratio 0.1, 95% CI 0.04-0.3) than for those who died in the community. The case-fatality rate was 68% (95% CI 60-74), and ETU admission was associated with a 50% reduction in death (hazard ratio 0.5, 95% CI 0.4-0.8). Isolation and treatment of Ebola patients had the dual benefit of interrupting community transmission and improving survival.

Keywords: Ebola; Ebolavirus Zaire; Liberia; basic reproduction number; case-fatality rate; disease outbreaks; epidemics; epidemiology; patient isolation; survival; viruses.

Figure 1

Communities in remote rural areas where Ebola virus disease outbreaks occurred, Liberia, August–December 2014. Size of red dot indicates number of cases.

Figure 2

Distribution of Ebola virus disease case-patients by number of secondary cases generated and admission to an Ebola treatment unit (ETU) in remote rural areas of Liberia, August–December 2014.

Figure 3

Number of Ebola virus disease secondary cases generated by case-patients, by time from symptom onset to start of interventions, in remote rural areas of Liberia, August–December 2014. Black circles indicate cases that occurred before the start of interventions (day 0); white circles indicate cases that occurred after interventions started.

Figure 4

Case-fatality rates for Ebola virus disease, by case-patient admission to an Ebola treatment unit (ETU) and month of symptom onset, in remote rural areas of Liberia, August–December 2014. Dashed lines indicate case-patients admitted to ETU; solid lines indicate patients not admitted to ETU. Error bars indicate 95% CIs.

Figure 5

Case-fatality rates for Ebola virus disease, by case-patient age group, in remote rural areas of Liberia, August–December 2014. Error bars indicate 95% CIs.

Figure 6

Kaplan-Meier survival curves comparing survival by admission to an Ebola treatment unit (ETU) in remote rural areas of Liberia, August–December 2014. Dashed lines indicate 95% CIs.