The researchers used data from 699 patients with confirmed EVD in Guinea between March 2014 and February 2015 to model the association between viraemia and case fatality ratio (CFR). They found the CFR for patients with low, intermediate, and high viraemia was 21%, 53%, and 81%, respectively. When the average viremia increased tenfold in July 2014, CFR increased as well, by 14%.
By knowing the relationship between viraemia and CFR, researchers will be able to more accurately assess the efficacy of treatments for EVD in nonrandomized trials, and by stratifying participants by viremia group researchers will be able to reduce the sample size needed for randomized trials by 25%.
Use of Viremia to Evaluate the Baseline Case Fatality Ratio of Ebola Virus Disease and Inform Treatment Studies: A Retrospective Cohort Study. (2015) PLoS Med 12 (12): e1001908. doi: 10.1371/journal.pmed.1001908
The case fatality ratio (CFR) of Ebola virus disease (EVD) can vary over time and space for reasons that are not fully understood. This makes it difficult to define the baseline CFRs needed to evaluate treatments in the absence of randomized controls. Here, we investigate whether viremia in EVD patients may be used to evaluate baseline EVD CFRs. Viremia in EVD patients was a strong predictor of death that partly explained variations in CFR in the study population. This study provides baseline CFRs by viremia group, which allow appropriate adjustment when estimating efficacy in treatment studies. In randomized controlled trials, stratifying analysis on viremia groups could reduce sample size require- ments by 25%. We hypothesize that monitoring the viremia of hospitalized patients may inform the ability of surveillance systems to detect EVD patients from the different severity strata.