Pauline Cafferkey, the U.K. nurse who was diagnosed with Ebola after returning home from Sierra Leone, was discharged from a London hospital nine months ago after she was thought to have made a full recovery.

The 39 year-old, however, is back in London's Royal Free Hospital's isolation unit due to a rare relapse of the virus. Doctors said that Cafferkey suffers from late complications of her previous Ebola infection.

In a statement released on Wednesday, Oct. 14, the hospital said that Cafferkey's condition has worsened and that she is now critically ill. Her family said that she fell ill on Oct. 5 but was initially advised by a doctor to return home.

Cafferkey was eventually admitted to Queen Elizabeth University Hospital in Glasgow, Scotland, where she lives, the following day as her condition worsened. She was later flown by military plane to receive treatment in London.

Experts said that Cafferkey's situation is unprecedented in medical terms. Molecular virology professor Jonathan Ball, from the University of Nottingham, said that while they are aware that the hemorrhagic disease can linger for many month after a patient appears cleared of visible symptoms and that the debilitating effects of Ebola can last for a long time, there has been no known case of a patient suffering from life-threatening complications months after recovery from the disease.

"But this is frankly staggering," Ball said. "I am not aware from the scientific literature of a case where Ebola has been associated with what we can only assume as life-threatening complications after someone has initially recovered, and certainly not so many months after."

National Health Service for Greater Glasgow and Clyde director of public health Emilia Crighton said that the risk of Cafferkey passing on the disease to anyone else was deemed "very low."

"In line with normal procedures in cases such as this, we have identified a small number of close contacts of Pauline's that we will be following up [with] as a precaution," Crighton said.

Nathalie MacDermott, from the Imperial College London, said that the nurse's condition was not anticipated and it is unlikely that something could have been done to prevent the reoccurrence of the virus.

She said that it is difficult to know if an earlier intervention may have changed Cafferkey's current condition because the medical community is still learning about the potential long-term effects of the disease and how to manage its complications and secondary effects.

On Sept. 28, Cafferkey was honored for her humanitarian work fighting Ebola in Sierra Leone at The Daily MIrror's Pride of Britain awards.