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Ebola is a rare virus that causes a disease with a high fatality rate. The most recent Ebola epidemic began in the African country of Guinea in December 2013. As of January 2016, over 11,000 deaths had been reported, mainly in West Africa.

Disease detectives

Many different kinds of health professionals have helped deal with the Ebola crisis. The doctors and nurses who work directly with patients are probably the first ones who spring to mind. But epidemiologists also have a key role to play in understanding Ebola and helping prevent the disease.

Epidemiologists are detectives who collect and analyze data related to diseases and other health conditions. They use this data to identify patterns, causes, and effects. Simply put, an epidemiologist is someone that studies epidemics.

Did you know? Patient Zero refers to the first victim of an epidemic. The patient zero of recent Ebola outbreak in Western Africa was likely Emile Ouanmouno, who may have been infected by a bat.

Fatality rate, reproduction number, prevalence, and incidence

For example, one common term used in epidemiology is the case fatality rate. It describes the proportion of deaths within a specific group of cases. The average case fatality rate for Ebola is around 50%. This means that 5 out of 10 people infected with Ebola die from it. In previous outbreaks of the disease, fatality rates have ranged from 25% to 90%.

Another metric used by epidemiologists is the reproduction number. It refers to the average number of people a typical infected person will pass the disease on to. If this number is greater than 1, then you can expect the number of cases to grow over time as the infection spreads through a population.

One estimate from 2015 put the reproduction number for Ebola in Liberia at 1.51. That means that each person infected with Ebola would pass the disease on to an average of 1.51 other people. During the same period, other researchers estimated the reproduction number to be 1.76 in Liberia and 1.49 in Sierra Leone. Keep in mind many of these statistics are estimates, and the numbers tend to change depending on the source of the data.

Two other important epidemiological concepts are prevalence and incidence. The prevalence of Ebola refers to the number of people who have Ebola at any given time. The incidence of Ebola refers to the number of new cases diagnosed over a specific time period, such as a year. In 2015, the prevalence of Ebola in Liberia and Sierra Leone was estimated at 0.049%. In February of that year, Guinea reported a sharp increase in the incidence of Ebola, with 65 new cases confirmed in one week, compared to 39 the week before.

Did you know? As of December 2015, there are no licensed Ebola vaccines. Two potential vaccines are being tested.

Epidemiologists studying Ebola calculate statistics like these using data gathered from healthcare workers and hospitals. More importantly, they can use the statistics to predict the spread of the disease and help authorities decide where resources are needed most.

Epidemiologists face many challenges during an event like an Ebola outbreak. They have to act fast to prevent the spread of the disease and try to figure out where the virus will most likely go next. Epidemiologists need to have a strong understanding of research methods and statistics. They also need to be excellent communicators as they often work with industry, policymakers, and healthcare workers.

Learn More!

Scientific publications on the Ebola virus:

Estimating the basic reproductive ratio for the Ebola outbreak in Liberia and Sierra Leone (2015)
A. Khan, M. Naveed, M. Dur-e-Ahmad & M. Imran, Infectious Diseases of Poverty 4

Estimating the Reproduction Number of Ebola Virus (EBOV) During the 2014 Outbreak in West Africa (2014)
C. L. Althaus, PLoS Currents 6

News articles on the Ebola outbreak in West Africa:

Latest Ebola outbreak over in Liberia; West Africa is at zero, but new flare-ups are likely to occur (2016)
World Health Organization

2014 Ebola outbreak in West Africa (2016)
Centers for Disease Control and Prevention

Ebola outbreak: 1st case with 2-year-old boy linked to bats (2014)
CBC News

What is the Ebola virus’s survival rate? And other key questions about the epidemic (2014)
S. Novack, S. Baker, D. Volz, National Journal

Measuring the impact of Ebola: Will it reach 1.4 million? (2014)
J. Michaud & J. Kates, The Henry J. Kaiser Family Foundation

Alvin Li

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