A recent study by Yale University has found that isolating Ebola victims within four days of symptom onset could achieve disease elimination in Liberia. Setting out to determine how to best use scare resources to combat the Ebola outbreak overwhelming West Africa, and after analyzing the incidence and case fatality of the outbreak, the team concluded that the best hope for ending the spread of Ebola was isolation of Ebola victims very early in the progression of symptoms–although the time window suggested by the research was smaller than current time to hospital reporting in West Africa.
“The Ebola outbreak in Western Africa is spiraling out of control. The need to determine how to deploy scarce resources to end this crisis is urgent,” the authors framed the study.
The goal of the study was to “evaluate the contribution of disease progression and case fatality to transmission and to examine the potential for targeted interventions to eliminate the disease,” the researchers wrote.
The team used both clinical and epidemiological data–incidence and case fatality records–from the Liberian Ministry of Health and Social Welfare, and found that secondary infections occurred during the infectious period of an Ebola victim at an average rate of 1.73. That is, each infected person passed on Ebola to 1.73 healthy individuals.
Ebola victims who did not survive passed the disease on to 0.66 people, while nonsurvivors passed the disease on to 2.36 people. Survivors of Ebola, the study found, infected at least one healthy person in 32 percent of cases. Nonsurvivors infected at least one healthy person with a 67 percent probability rate.
“Consequently, nonsurvivors, who made up 63% (CI, 60% to 64%) of the population, were responsible for 86% (CI, 63% to 98%) of transmissions,” the researchers found.
Left alone, the disease would double every 20 days, the researchers calculated.
The conclusion reached by the team was that isolation of infected individuals offered a chance of eliminating the disease. Isolation of 75 percent of nonsurviving infected individuals within four days after symptoms began created a 74 percent chance of disease elimination, Adding isolation of all infected offered a marginal reduction beyond the 74 percent.
The researchers pointed out, however, that it was impossible to predict survival at the onset of symptoms, so isolation would have to be for all or most infected individuals who are in critical condition within four days of onset.
Further, the researchers noted that the current average period from symptom onset to hospitalization in Liberia was approximately 5 days–significantly beyond the requirements suggested by the study.
“These results underscore the importance of isolating the most severely ill patients with Ebola within the first few days of their symptomatic phase,” the researchers wrote.
The researchers also evaluated the effectiveness of self-quarantine–a pragmatic strategy in areas where there were not sufficient isolation units. Self-quarantine of 75 percent of all infected could eradicate Ebola with 78 percent probability.
Self-quarantine would require reducing contact by 60 percent, however, and this was found to be beyond the normal occurrence.
The researchers concluded that the assistance offered to address the Ebola outbreak “should be directed towards expanding the capacity of hospitalized case isolation.”
“Targeted isolation may offer the best hope of ending the Ebola epidemic.”
The report, “Effect of Ebola Progression on Transmission and Control in Liberia,” was authored by Dan Yamin, PhD; Shai Gertler; Martial L. Ndeffo-Mbah, PhD; Laura A. Skrip, MPH; Mosoka Fallah, PhD; Tolbert G. Nyenswah, MPH; Frederick L. Altice, MD, MA; and Alison P. Galvani, PhD, was published in Annals of Internal Medicine, and was funded primarily by the National Institute of Health.
By Andrew Stern
Photo: International Federation of Red Cross and Red Crescent Societies
Isolating Ebola Cases Best Chance of Eradicating Ebola - Report
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