A new study finds that a small number of people, referred to as 'superspreaders,' may have been responsible for nearly two-thirds of Ebola cases during the 2014-2015 epidemic in West Africa.

Although superspreaders have been previously thought to play a small role in the transmission of Ebola, this study allowed scientists to better understand and measure how superspreaders fueled the epidemic.

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The researchers analyzed community-based data collected around Freetown, the capital of Sierra Leone. These data included GPS locations of 200 dead bodies that tested positive for Ebola, as well as the age, sex, time of burial, and symptom onset time, as reported retrospectively by next of kin. This data allowed the scientists to focus on the cases of people who weren't hospitalized, and who were not detected through formal surveillance methods.

Age was found to be a key demographic for superspreading. Specifically, children younger than 15 and adults ages 40 to 55, co-author of the study Benjamin Dalziel, told the Washington Post.

While this is an important finding, the researchers note that further work needs to be done to link factors such as age to viruses and the diseases caused by them. Additionally, this may allow for interventions to be developed targeted at smaller groups, rather than dealing with a large population.

The research was led by Princeton University and reported this week in Proceedings of the National Academy of Sciences.

Ebola is a virus that has symptoms including fever, headache, muscle pain, chills, and sometimes internal bleeding which leads to vomiting and coughing blood. The 2014 West African outbreak was the largest Ebola outbreak in history and two in five people who got Ebola during this time died, according to the Centers for Disease Control and Prevention.

This is not the first time superspreaders have been identified in the spread of infectious disease, the study notes. Other notable cases include the Middle East respiratory syndrome (MERS) outbreak starting in 2012, the severe acute respiratory syndrome, or SARS, pandemic in 2003, the measles outbreak in Finland in 1989, and the spread of Typhoid fever by the infamous “Typhoid Mary” in New York City in the early 1900s.

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