A patient in has tested positive for the virus, health officials said Friday, more than two weeks after the last known case in the country had been discharged from the hospital.
The news deflated optimism that , one of the three West African countries hit by the epidemic that has killed more than 10,000 people since it began a year ago, would soon be officially declared free of the virus.
The patient, a 44-year-old woman from the Caldwell area near Monrovia, the capital, first developed symptoms around March 15, said Dr. Moses Massaquoi, leader of the Clinton Health Access Initiative in Liberia and national case manager of the Ebola response.
Health officials said it was unclear how the woman, a food seller, had been infected. She had not been on a monitoring list for possible exposure and she said she had not traveled outside Liberia. The Information Ministry issued a statement saying “initial suspicion is that it may be the result of possible sexual intercourse with an Ebola survivor.”
While that is only speculative, researchers have found evidence that Ebola may persist in semen for up to three months after recovery, and abstinence is recommended.
In part for this reason, the World Health Organization intends to release new guidelines for when an Ebola epidemic ends, a W.H.O. official said.
To be declared Ebola-free, countries must wait 42 days from when the last patient tests negative for a second time. The new guidelines would recommend “heightened surveillance” for an additional 90 days, to take into account the potential for sexual transmission and hidden transmission chains.
Two Liberian triage nurses employed by the International Rescue Committee, an American relief agency, recognized the patient’s symptoms when she arrived at Monrovia’s Redemption Hospital on Thursday, Liz Hamann, the agency’s project leader, said from Monrovia.
Acting on a well-rehearsed protocol, the nurses summoned a team from an adjacent Ebola isolation center run by Doctors Without Borders, who arrived in protective gear and took the patient for testing. The initial results came back positive on Friday. “We were all a little blindsided,” Ms. Hamann said.
Dr. David Nabarro, the United Nations secretary general’s special envoy on Ebola, was informed of the new case while traveling in Italy. He expressed disappointment but not surprise.
“We will have unfortunately some periods in which our hopes are dashed at this stage in the outbreak,” he said in a telephone interview. “That’s just the way it is. That’s why we’re going to have to keep going without any kind of letup until the very end.”
New cases have declined sharply since last fall, when hundreds were becoming infected every week in Liberia, Guinea and Sierra Leone. Liberia has made the most progress.
On March 5, what was thought to have been Liberia’s last patient was discharged, a celebratory moment.“We knew something like this could possibly happen, so we have all the necessary setup in place to address it,” Dr. Massaquoi said. Still, he said, “today has not been a good day for us.”
Liberia’s comeback has been considered a model of community organizing, which raised public awareness of the risks of transmission through physical contact and unsafe burials. Dr. Bruce Aylward, the World Health Organization’s top Ebola official, described the nurses who first suspected the new Liberia case as heroes.
“They may have protected the whole country by finding the needle in the haystack,” he said in a phone interview. “It was because they were searching that haystack for the needle.”