"Long before it's in the papers"
January 27, 2015


Study: isolating only “likely non-survivors” can stop Ebola

Oct. 27, 2014
Courtesy of the American College of Physicians
and World Science staff

I­so­lat­ing the sick­est Ebola pa­tients with­in four days of symp­tom on­set would elim­i­nate the Ebola ep­i­dem­ic in Li­be­ria, ac­cord­ing to a newly pub­lished mod­el­ing stu­dy.

Ac­cord­ing to the stu­dy, iso­lat­ing only “likely non-sur­vivors” would be enough, be­cause they are the most con­ta­gious group. The study is pub­lished Oct. 28 online in the jour­nal An­nals of In­ter­nal Med­i­cine.

West Af­ri­ca is suf­fer­ing the larg­est and dead­li­est Ebola ep­i­dem­ic ev­er recorded. Li­be­ria has been es­pe­cially hard-hit with more than 3,500 in­fec­tions and 2,000 deaths in the past three months. About 70 per­cent of Ebola pa­tients die in West Af­ri­ca, al­though ex­perts at­trib­ute the high mor­tal­ity rate partly to lack of mod­ern med­i­cal care in the ar­ea.

In the stu­dy, Ka­ren N. Peart of Yale Uni­vers­ity and col­leagues de­vel­oped a mod­el known as random-trans­mis­sion to see how dis­ease pro­gres­sion and case fa­tal­ity af­fect trans­mis­sion, and the ef­fects of pa­tient isola­t­ion. They found that the risk for trans­mit­ting Ebola de­pends on the vi­ral load, or amount of vi­rus­es, in an in­fected per­son, and the num­ber of peo­ple with which he or she in­ter­acts.

Dis­tin­guish­ing be­tween sur­vivors and non-sur­vivors is im­por­tant, they said, be­cause sur­vivors tend to achieve peak vi­ral load about four days af­ter symp­toms de­vel­op; then vi­ral load de­clines. But in non-sur­vivors, with more sev­ere symp­toms, vi­ral load is 100 times high­er than that of sur­vivors through­out in­fec­tion and does­n’t de­cline af­ter peak.

The sur­vivors were found to have a 32 per­cent prob­a­bil­ity of in­fect­ing at least one oth­er per­son. Non-sur­vivors have more than twice the prob­a­bil­ity of in­fect­ing some­one else—67 per­cent, the study found.

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Isolating the sickest Ebola patients within four days of symptom onset would eliminate the Ebola epidemic in Liberia, according to a newly published modeling study. According to the study, isolating only “likely non-survivors” would be enough, because they are the most contagious group. The study is being published in the journal Annals of Internal Medicine. West Africa is suffering the largest and deadliest Ebola epidemic ever recorded. Liberia has been especially hard-hit with more than 3,500 infections and 2,000 deaths in the past three months. About 70 percent of Ebola patients die in West Africa, although experts attribute the high mortality rate partly to lack of modern medical care in the area. In the study, Karen N. Peart of Yale University and colleagues developed a model known as random-transmission to see how disease progression and case fatality affect transmission, and the effects of patient isolation. They found that the risk for transmitting Ebola depends on the viral load, or amount of viruses, in an infected person, and the number of people with which he or she interacts. Distinguishing between survivors and non-survivors is important, they said, because survivors tend to achieve peak viral load about four days after symptoms develop; then viral load declines. The survivors were found to have a 32 percent probability of infecting at least one other person. But in non-survivors, with more severe symptoms, viral load is 100 times higher than that of survivors throughout infection and doesn’t decline after peak. They also have more than twice the probability of infecting someone else—67 percent, the study found.