Heterogeneities in the case fatality ratio in the West African Ebola outbreak 2013–2016

Abstract

The 2013–2016 Ebola outbreak in West Africa is the largest on record with 28 616 confirmed, probable and suspected cases and 11 310 deaths officially recorded by 10 June 2016, the true burden probably considerably higher. The case fatality ratio (CFR: proportion of cases that are fatal) is a key indicator of disease severity useful for gauging the appropriate public health response and for evaluating treatment benefits, if estimated accurately. We analysed individual-level clinical outcome data from Guinea, Liberia and Sierra Leone officially reported to the World Health Organization. The overall mean CFR was 62.9% (95% CI: 61.9% to 64.0%) among confirmed cases with recorded clinical outcomes. Age was the most important modifier of survival probabilities, but country, stage of the epidemic and whether patients were hospitalized also played roles. We developed a statistical analysis to detect outliers in CFR between districts of residence and treatment centres (TCs), adjusting for known factors influencing survival and identified eight districts and three TCs with a CFR significantly different from the average. From the current dataset, we cannot determine whether the observed variation in CFR seen by district or treatment centre reflects real differences in survival, related to the quality of care or other factors or was caused by differences in reporting practices or case ascertainment.This article is part of the themed issue ‘The 2013–2016 West African Ebola epidemic: data, decision-making and disease control’.

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“…The high mobility of the population across borders and closer proximity to urban centers, even when living remotely, will probably have increased transmission frequency in the three heavily affected countries (Coltart et al, 2017; WHO Ebola Response Team et al, 2016). Higher survival rates of patients and virus persistence in convalescents may have further increased the chances for transmission (Garske et al, 2017; Sissoko et al, 2017a, 2017b). These are only a few examples of many more that should be considered and investigated.…”

Delayed recognition of Ebola virus disease is associated with longer and larger outbreaks

“…Although some experts had maintained that EVD was a perennial threat of significant public health concern [16], it had largely come to be regarded as a minimal threat that was confined to remote populations and of very limited outbreak potential, insignificant in comparison to other infectious diseases [17,18]. Ultimately, however, approximately 30,000 cases were reported during the west Africa outbreak [19] ( Figure 4B)two orders of magnitude greater than any preceding outbreak and over 20 times the total of all previously known casesand at 888 days in duration it was nearly four times longer than any previous outbreak (Figures 1 and 4A). EVD patients from the outbreak eventually reached 15 different countries spanning three continents as part of transmission chains or for medical treatment (Table 1), with Guinea, Liberia, and Sierra Leone at the epicenter.…”

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“…Some heterogeneity in severity and transmissibility could be identified (e.g. by age and viraemia [7,10,116,125,[130][131][132]), but other types of heterogeneity could not be assessed. For example, it was not possible to compare the CFR between hospitalized and non-hospitalized cases, because of biases in the way cases were recorded in the line-list [28].…”