At least half and as many as 83 percent of all Ebola outbreaks in West Africa go unreported, according to a study published in PLOS Neglected Tropical Diseases.
To conduct the study, researchers analyzed three data sets on the distribution of secondary Ebola infections from outbreaks in three geographic areas: all of West Africa, the Western Area district of Sierra Leone, and the city of Conakry in Guinea. They found at least half of all outbreaks have gone unreported since Ebola's discovery in 1976, representing over 100 cases.
The study also found single cases are more likely to be detected when part of a larger outbreak. Ebola has a low reported rate of transmission, and single cases often occur without infecting anyone else. Yet early detection of these individual cases can prove crucial to outbreak prevention.
"These findings highlight the importance of primary healthcare and local case management to detect and contain undetected early stage outbreaks at source," the study said.
Over 1,400 people have died in the Congo's current outbreak, which has now spread to Uganda.