A recent study published in Proceedings of the National Academy of Sciences has found that the majority of infections during the 2014-2015 Ebola outbreak in West Africa were due to superspreaders, people who transmit an infectious agent to disproportionately more people than others with the same infection. Researchers at Princeton University and Oregon State University analyzed the timing and location of 200 community burials during the outbreak in the urban areas around Freetown, the capital of Sierra Leone. They used a model to reconstruct the web of transmissions and found that approximately 61% of cases could be traced back to just 3% of the people infected. This pattern was also found in Guinea and Liberia.
Superspreaders tended to be children under the age of 15 and adults over 45. It is thought that this association was due to younger and older individuals being more likely to be cared for by others. In addition, older people were more likely to be in charge of organizing large funerals, during which transmission often occurred since Ebola spreads primarily through contact with bodily fluids. Transmission was more likely to occur at the local community level rather than in health care facilities. A better understanding of factors associated with superspreading can help inform methods of controlling outbreaks.
Lau MSY, Dalziel BD, Funk S, et al. "Spatial and temporal dynamics of superspreading events in the 2014-2015 West Africa Ebola epidemic." PNAS. 2017. doi: 10.1073/pnas.1614595114
Sun LH. "Disease 'superspreaders' accounted for nearly two-thirds of Ebola cases, study finds." The Washington Post. 2017. https://www.washingtonpost.com/news/to-your-health/wp/2017/02/13/disease-superspreaders-accounted-for-nearly-two-thirds-of-ebola-cases-study-finds/?utm_term=.bbac463b23d2