London's Royal Free Hospital says a Scottish nurse it is treating for Ebola is in critical condition.
The hospital said Saturday that Pauline Cafferkey's condition has deteriorated over the past two days.
Cafferkey had been volunteering on the anti-Ebola effort in Sierra Leone last month before she fell ill. She returned to Britain on December 28 and was diagnosed with the virus two days later.
Cafferkey was the first Ebola patient to be diagnosed in Britain. The Royal Free Hospital in August successfully treated British aid worker William Pooley with the experimental drug ZMapp, but the hospital said no ZMapp supplies were available by the time Cafferkey was diagnosed.
Health care officials said Cafferkey is being treated with blood plasma from an Ebola survivor and an experimental drug which it did not name.
Cafferkey's decline has been rapid. On December 31, her doctor said she was sitting up in bed, talking, and reading.