A fourth American who contracted Ebola in West Africa is expected to arrive in the US for care on Tuesday and will be treated at a hospital where two other aid workers recovered from the disease.
Emory University Hospital in Atlanta says the patient will be treated there but hasn't released any other information.
However, the World Health Organisation says one of its doctors who has been working in an Ebola treatment centre in Sierra Leone has tested positive for the disease.
It says the doctor is in a stable condition in Freetown and will be evacuated.
Last month, two aid workers who contracted Ebola while working in Liberia were treated successfully at Emory.
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A third patient, 51-year-old American doctor Rick Sacra, remains in a stable condition in a Nebraska facility, but his recovery remains uncertain.
