The outbreak is likely on a scale larger than realized, says WHO, and attributes that to various factors including keeping infected family members at home to die, denial of infection and fear that medical quarantine will be lethal to ill family members.
"As Ebola has no cure, some believe infected loved ones will be more comfortable dying at home."
In rural villages in particular, locals do not notify health officials when a resident dies from Ebola symptoms, leading to an underestimate of the real number of cases.
Many medical facilities are overwhelmed and ill-equipped to handle the enormity of need.
In Liberia, WHO also noted a new phenomenon of "an invisible caseload of patients who are not being detected by the surveillance system" but show up at alarmingly high rates whenever a new treatment facility is opened.
WHO cited another issue affecting the accurate reporting of Ebola cases. In some villages WHO has termed "shadow zones," there are rumored Ebola cases "that cannot be investigated because of community resistance or lack of adequate staff and vehicles."
WHO said its epidemiologists in Sierra Leone and Liberia are working with Doctors without Borders and the CDC and other agencies in order to produce more accurate estimates of infection from Ebola.
As of Wednesday, WHO had recorded 2,615 cases of confirmed, possible and suspected Ebola in Guinea, Liberia, Nigeria and Sierra Leone, including 1,427 deaths.