Effect of Ebola Progression on Transmission and Control in Liberia

Abstract

Background The Ebola outbreak that is sweeping across West Africa is the largest, most volatile, and deadliest Ebola epidemic ever recorded. Liberia is the most profoundly affected country, with more than 3500 infections and 2000 deaths recorded in the past 3 months. Objective To evaluate the contribution of disease progression and case fatality on transmission and to examine the potential for targeted interventions to eliminate the disease. Design Stochastic transmission model that integrates epidemiologic and clinical data on incidence and case fatality, daily viral load among survivors and nonsurvivors evaluated on the basis of the 2000–2001 outbreak in Uganda, and primary data on contacts of patients with Ebola in Liberia. Setting Montserrado County, Liberia, July to September 2014. Measurements Ebola incidence and case-fatality records from 2014 Liberian Ministry of Health and Social Welfare. Results The average number of secondary infections generated throughout the entire infectious period of a single infected case, R, was estimated as 1.73 (95% CI, 1.66 to 1.83). There was substantial stratification between survivors (RSurvivors), for whom the estimate was 0.66 (CI, 0.10 to 1.69), and nonsurvivors (RNonsurvivors), for whom the estimate was 2.36 (CI, 1.72 to 2.80). The nonsurvivors had the highest risk for transmitting the virus later in the course of disease progression. Consequently, the isolation of 75% of infected individuals in critical condition within 4 days from symptom onset has a high chance of eliminating the disease. Limitation Projections are based on the initial dynamics of the epidemic, which may change as the outbreak and interventions evolve. Conclusion These results underscore the importance of isolating the most severely ill patients with Ebola within the first few days of their symptomatic phase. Primary Funding Source National Institutes of Health.

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.…”

Ebola virus disease outbreak in Nigeria: lessons to learn

“…Third, we assumed that EVD cases are equally infectious throughout their infectious period. However, transmissibility could increase with disease progression due to higher viral loads (Yamin et al, 2014). This could explain the sudden increase in cases during the second week as most of these were probably infected shortly before the index case died.…”

Retrospective Analysis of the 2014–2015 Ebola Epidemic in Liberia

“…Behavioral response to an epidemic, particularly one of such a deadly disease as Ebola, can significantly impact transmission. [15][16][17] In the general community, heightened awareness about Ebola may have spurred behavioral changes that reduce an individual's exposure risk, for example, limiting direct contact (e.g., handshaking) and improved sanitation (e.g., handwashing). 16 Widespread public awareness may be the result of personal observations of Ebola victims, word-of-mouth and targeted public health campaigns.…”