An estimated half of Ebola virus disease outbreaks have gone undetected since it was discovered in 1976, according to research published in PLOS Neglected Tropical Diseases. Although these tend to affect fewer than five patients, the study, led by Emma Glennon at Cambridge University, highlights the need for improved detection and rapid response, in order that outbreaks of Ebola and other public health threats are detected early and consistently.

The authors used three independent datasets from the 2013-16 Ebola outbreak in West Africa: in a district of Sierra Leone, in the city of Conakry in Guinea, and throughout the whole region whole region of the outbreak. Taking the properties of person-to person disease transmission, the team simulated realistic outbreak size distributions and compared them to reported outbreak sizes. Their median estimates suggest that at least half of Ebola outbreaks have gone undetected and this could represent well over 100 patient cases. The research also found that an individual patient's probability of detection is dependent on the size of the cluster of cases, with less than 10% chance of detecting a single-case event.

This is the first study to quantitatively estimate the number of undetected Ebola outbreaks and makes the case for greater investment in primary health care and local surveillance. Most undetected cases are handled locally, where core health infrastructure often lacks basic provisions for infectious disease diagnosis and control. Supporting public health and sanitation infrastructure in areas where outbreaks occur could prevent small outbreaks growing into larger events. Increasing local capacity to accurately diagnose and treat Ebola and other infectious diseases has the potential to improve surveillance and increase early detection of all outbreaks.