FREETOWN, Sierra Leone (AP) — Health officials in Sierra Leone on Sunday confirmed an Ebola death less than a week after the country's last known patient was discharged from a hospital.

Samples from the body of a 67-year-old woman who died recently in Kambia district in the country's north came back positive for the deadly disease, said chief medical officer Dr. Brima Kargbo.

Last Monday, the last known Ebola patient was released from a hospital in Sierra Leone, a milestone that allowed the West African nation to begin a 42-day countdown toward being declared free of Ebola transmission.

Authorities were still trying to determine whether the woman in Kambia died before or after that countdown began, Kargbo said.

The National Ebola Response Center had deployed teams to conduct surveillance and trace people who were in contact with the woman, said OB Sisay, the center's director.

"We should not despair as we have been expecting this," Sisay said. "We need to stay focused and maintain our discipline."

The worst Ebola outbreak in history has killed nearly 4,000 people in Sierra Leone out of more than 13,500 confirmed, probable and suspected cases, according to the World Health Organization. More than 11,300 people have died in the outbreak, mostly in Guinea, Sierra Leone and Liberia.

A country must go 42 days — equal to two incubation periods of 21 days — without an Ebola case in order for WHO to declare it free of Ebola transmission. It's a benchmark that neighboring Liberia reached in May only to then experience a brief reappearance of cases.