FREETOWN, Sierra Leone -- A woman who died this week in Sierra Leone tested positive for Ebola, officials said Friday, a setback for the region that comes only a day after the World Health Organization had declared the epidemic over.
WHO had warned Thursday that new Ebola cases were possible even after the virus' spread was halted in Liberia, Sierra Leone and Guinea -- the three West African nations hardest hit by the epidemic that left more than 11,300 people dead.
Already 10 other flare-ups have taken place in areas where the spread of Ebola was thought to have ended, raising new questions about WHO procedures in assessing whether an epidemic was really over.
The U.N. health agency said Friday that Sierra Leone's government was moving rapidly to contain the new threat, but it was not immediately clear how the 22-year-old woman who died may have contracted Ebola -- all known transmission chains in that country were halted in November.
Francis Langoba Kellie, a spokesman for Sierra Leone's Office of National Security, said on the radio that the woman had come from the country's Northern Kambia District and had gone to the Northern Tonkolili District for medical care.
Authorities are tracing her contacts and have dispatched teams to the area to investigate how she might have contracted the deadly virus and if she might have infected others. Certain areas will be quarantined, he said, without elaborating.
Dr. Bruce Aylward, who heads WHO's Ebola response efforts, said the woman was not buried safely because local health workers had not identified her as a suspected Ebola case. That raises the possibility there could be a wider Ebola outbreak.
"The world now is acutely aware that yes, this risk does continue," Aylward said. He called the announcement of Sierra Leone's latest case on Friday "unfortunate timing."
WHO declared the latest Ebola outbreak over in Liberia on Thursday after no new cases emerged there during a 42-day waiting period. That benchmark had already been met in both Guinea and Sierra Leone.
Aylward said WHO was not reconsidering its 42-day waiting period despite the repeated re-emergence of new cases after Ebola outbreaks had been announced as over in countries.
"(Sierra Leone's) level of preparedness and response capabilities are very high and there is no cause for concern," said Kellie. "We encourage the public to continue to practice the hygiene regulations which were in force during the period while Ebola was raging and the emergency regulations are still in force."
Ebola is spread through direct contact with the bodily fluids of people who are sick or the bodies of the dead.
WHO says flare-up cases, such as in Liberia, "are likely the result of the virus persisting in survivors even after recovery." Of particular concern is that Ebola can stay in the semen of some male survivors up to a year later. The WHO said Thursday that Ebola can "in rare instances, be transmitted to intimate partners." Ebola can also jump to humans from animals like monkeys and bats.
WHO declares Ebola transmission over when a country goes through two incubation periods -- 21 days each -- without a new case emerging. Countries are then placed on a 90-day heightened surveillance. Sierra Leone was first declared Ebola-free on Nov. 7, after nearly 4,000 people had died from the virus there.
