A dead patient in Sierra Leone has tested positive for Ebola, an official said Friday, just a day after the World Health Organization declared the outbreak over in West Africa. Ebola has killed more than 11,300 people, mostly in West Africa, since it emerged at the end of 2013.

Two tests on a 22-year-old woman who died earlier this month in Sierra Leone tested positive for the deadly virus. The tests were carried out by British health organization Public Health England in Tonkolili district, east of the capital Freetown, Reuters reported, citing the spokesman for the Health Ministry. Authorities reportedly said that they were trying to trace people the deceased was in contact with.

On Thursday, Liberia was declared Ebola-free after no new cases were found in 42 days. Last year, Guinea and Sierra Leone — two other hardest-hit nations — were declared free of Ebola.

Liberia was declared free of the Ebola virus twice last year — in May and September — but each time a new case emerged.