By William James and Andy Bruce
LONDON, Dec 30 (Reuters) - A health worker who has become the first person to be diagnosed with Ebola in Britain was being treated at a London hospital on Tuesday after contracting the disease in West Africa.
The woman arrived from Scotland at the Royal Free hospital, Britain's designated Ebola treatment center, in an ambulance accompanied by police vehicles, a Reuters witness said.
"The latest update we have on the condition of the patient is that she is doing as well as can be expected in the circumstances," Scottish First Minister Nicola Sturgeon said.
The Royal Free Hospital confirmed the patient was being treated for the Ebola virus, and named her as Pauline Cafferkey, a 39-year-old nurse with 16 years experience who normally works at a Scottish health center.
The London hospital's "High-level isolation unit" will allow doctors to treat Cafferkey while she lies in a plastic tent, limiting the scope for the disease, which is transmitted by contact with bodily fluids, to be passed to medical staff.
Officials said three other patients were being tested for Ebola in Britain.
One of them, who was described by Sturgeon as a "low probability" case in Scotland, has tested negative for the disease. The health service said the second possible case was in Cornwall, England, and details were not available on the third.
The World Health Organization said on Monday that the number of people infected by Ebola in the three West African countries worst affected by the outbreak - Sierra Leone, Liberia and Guinea - had passed 20,000, with more than 7,842 deaths so far.
Cafferkey, a National Health Service worker who had been working in West Africa with the charity Save the Children, flew from Sierra Leone to Glasgow late on Sunday on a British Airways flight via Casablanca in Morocco and London's Heathrow.
Health officials said she was screened for a high temperature with other returning health workers at Heathrow but showed no signs of fever. She requested further screening at the airport but six subsequent checks were within normal levels.
She was diagnosed with the virus on Monday after developing symptoms overnight and was initially treated at a Scottish hospital.
Local media said she had been working in the Kerry Town Ebola treatment center outside Sierra Leone's capital, Freetown.
A Reuters journalist who visited the center last week said it was a huge, pristine facility built by British army engineers, with around 80 beds and stringent cleansing procedures far superior to those of a nearby Sierra Leonean treatment center.
With paths laid with new gravel and whitewashed walls, the center even had a gazebo in the "red zone" for recovering patients to sit and chat. Child patients were given a cuddly toy on arrival. On discharge, the toys would have to stay inside the red zone, so each child was given a new, ebola-free toy.
At every doorway there was a barrel of disinfectant. Health workers preparing to enter the red zone all had spotters to check equipment as they changed into protective clothing.
Authorities said Cafferkey was diagnosed early, meaning the risk to others was extremely low, but they were investigating all possible contacts with her.
"I'm satisfied ... that the procedures, the protocols, the things that we've been practicing now for months and months have now kicked in," health minister Jeremy Hunt said.
Britain began screening passengers from West Africa for symptoms of Ebola in October. Hunt said then that he expected to see "a handful" of cases arriving in Britain.
Earlier this year the Royal Free hospital successfully treated another British aid worker, William Pooley, who was flown home after being diagnosed with the virus in Sierra Leone.
England's Chief Medical Officer Sally Davies said blood plasma donated by Pooley during his "recovery phase" could be used to help treat Cafferkey.
Around 200 people have been assessed or tested for the virus in recent months, Paul Cosford, Director for Health Protection at Public Health England, the government body handling Britain's response to Ebola, told the BBC. (Additional reporting by Neil Hall, Liisa Tuhkanen, Ruairidh Villar and Li-mei Hoang; Editing by Andrew Heavens/Dominic Evans/Susan Fenton/Giles Elgood/David Stamp)