Ebola outbreak projected to exceed 20,000 cases by November

1. The outbreak of Ebola has been declared a public health emergency by the World Health Organization.

2. This study reports on data collected in the first 9 months of the outbreak, and suggests that the case-fatality rate in patients with definitive outcomes is 70.8%.

3. The outbreak continues to expand, and is expected to involve more than 20,000 reported cases by early-November 2014.

Evidence Rating Level: 2 (Good)

Study Rundown: The current outbreak of Ebola virus disease (EVD) started in December 2013 in Guinea, and has since spread to Liberia, Nigeria, Senegal, and Sierra Leone. The World Health Organization (WHO) was notified of the worsening outbreak in March 2014, and subsequently declared it a “public health emergency of international concern” on August 8, 2014. As of September 20, 2014, there were 5,843 confirmed, probable, or suspected cases with 2,803 deaths attributed to the current outbreak. It is known that the magnitude of the outbreak is larger than what is captured in official statistics, as many infections and deaths are not documented. Despite widespread efforts to control the outbreak, the number of cases and deaths from EVD continues to rise at a rapid pace.

The purpose of this study is to describe the clinical and epidemiological characteristics of the outbreak in its first 9 months, and to project further spread if control measures are not improved. Based on patients with definitive outcomes, it was calculated that the case-fatality rate was 70.8% (95%CI 68.6-72.8%). Modeling of the spread of infection suggests that the outbreak is still expanding. At current rates of spread and with no change in control efforts, it is estimated that the reported case load will exceed 20,000 by early-November 2014, with the true case load being significantly higher.

Click to read the study, published today in NEJM

Click to read an accompanying editorial, published today in NEJM

Relevant Reading: Ebola haemorrhagic fever

In-Depth [epidemiologic investigation]: Clinical and demographic data were collected using a standard case investigation form, and this was supplemented by information from informal case reports, diagnostic laboratories, and burial records.

This study reports on a total of 4,507 confirmed and probable cases of EVD reported to WHO from December 30, 2013 to September 14, 2014. Notably, 718 confirmed or probable cases and 289 deaths were reported in the most recent week alone. The median age of patients with EVD was 32 years, and the majority of patients were between 15 and 44 years of age (60.8%). The most common symptoms reported were fever (87.1%), fatigue (76.4%), loss of appetite (64.5%), vomiting (67.6%), and diarrhea (65.6%). Hemorrhagic symptoms were rarely reported (<1 to 5.7% of patients), though unexplained bleeding was more common (18.0%).

Case-fatality estimates were challenging to estimate, given that many cases did not have definitive recorded outcomes. In patients with definitive outcomes, case-fatality was calculated to be 70.8% (95%CI 68.6-72.8%), which was consistent among Guinea, Liberia, and Sierra Leone. Significant risk factors for death included age ≥45 years (OR 2.47; 95%CI 1.79-3.46), diarrhea (OR 1.42; 1.06-1.89), and unexplained bleeding (OR 1.83; 95%CI 1.20-2.90), amongst others.

Based on quantification of the spread of infection, it was found that the current outbreak is still expanding, with doubling times of 15.7 days in Guinea, 23.6 days in Liberia, and 30.2 days in Sierra Leone. At the current rates of expansion and with no change in efforts to limit further spread, it is estimated that there will be more than 20,000 cases by November 2, 2014.

Image: PD/CDC

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