Liberian officials were investigating Saturday how the country's latest Ebola patient became infected, after weeks with no cases of the disease in the country.
Liberia has seen the most deaths in the Ebola outbreak, with more than 4,200 of the more than 10,000 dead across West Africa.
Since Liberia discharged its last case on March 5, it was counting down the 42 days that a country must wait in order to be declared Ebola-free. But on Friday, officials said a new patient tested positive.
In a worrying sign, she doesn't seem to be linked to any of the people on an Ebola contacts list and said she has not traveled recently to the neighboring infected countries of Sierra Leone and Guinea, said Dr. Francis Kateh, acting head of the Liberia Ebola Case Management Team.
Kateh said authorities were considering the possibility that she had a visitor from outside Liberia who infected her or that she had sex with a survivor. The Ebola virus can be found in the semen of survivors for up to three months, and health authorities recommend that survivors abstain from sex during that period.
"The key thing is, if there is any transmission out there, how can we break this transmission?" he asked.
President Ellen Johnson Sirleaf is calling the investigation team every half-hour or so to check in, Kateh said.
Authorities are still compiling a list of people who came into contact with the patient, said Elizabeth Hamann of the International Rescue Committee, which is helping to manage the hospital where the woman first sought care. Contacts of people who are sick with Ebola must be monitored for symptoms.
Although hopes were high that Liberia had beaten Ebola, officials know that until neighboring Sierra Leone and Guinea also stamp out the disease, Liberia will remain at risk.