Health authorities quarantined hundreds of people in northernSierra Leone on Monday after a 16-year-old girl died of Ebola in an apparent case of sexual transmission, the first confirmed death from the virus in the district for nearly six months. Sierra Leone celebrated last month when it discharged the last remaining Ebola patient from its treatment centres. But since then a new spate of cases has erupted, leaving two dead and five people in treatment. The worst outbreak of Ebola on record has killed more than 11,000 people in Sierra Leone, Guinea and neighbouringLiberia since it began in December 2013. Liberia was declared Ebola-free this month but growing evidence that the virus may survive longer than previously thought in sperm has raised fears of fresh outbreaks. The teenage girl, Kadiatu Thullah, died on Sunday at theInternational Medical Corps Ebola treatment unit, authorities said.

Emmanuel Conteh, head of the Ebola Response Centre for the district of Bombali in northern Sierra Leone, said that some 690 people in the village of Robuya where Kadiatu lived would be isolated for three weeks. "Seven of her primary contacts have been taken to the Ebola treatment unit," he told Reuters. Three patients who came into contact with the girl at another health facility have also been taken to the treatment unit. Conteh said health workers were investigating how the teenager got infected, since she had not travelled outside the village in years. Initial suspicions are that she had sex with an Ebola survivor. "We are baffled by that possibility because the survivor in question was discharged in March, way beyond the 90-day period within which sexual transmission is said to be possible," Conteh said.