Health experts continue to investigate how a man contracted a potentially fatal Sars-like virus.
The 49-year-old, from Qatar, is being treated at an intensive care unit in a London hospital after becoming infected with a new type of coronavirus, said the World Health Organisation (WHO).
Coronaviruses cause most common colds but can also cause Sars (severe acute respiratory syndrome). In 2003, hundreds of people died after a Sars outbreak in Asia.
The patient, who was suffering from acute respiratory syndrome and renal failure, was admitted to an intensive care unit in Doha, Qatar, on September 7. He was transferred to the UK by air ambulance on September 11.
Before he became ill he had travelled to Saudi Arabia, a WHO spokesman said.
The Health Protection Agency (HPA) said the man has contracted a "new virus" which has only been identified in one other case. That patient, a 60-year-old from Saudi Arabia, died as a result of the virus. A HPA spokeswoman said preliminary inquires had found no contact between the two patients.
Professor John Watson, head of the respiratory diseases department at the HPA, said: "In the light of the severity of the illness that has been identified in the two confirmed cases, immediate steps have been taken to ensure that people who have been in contact with the UK case have not been infected, and there is no evidence to suggest that they have.
"As we are aware of only two cases worldwide and there is no specific evidence of ongoing transmission, at present there is no specific advice for the public or returning travellers to take but we will share any further advice with the public as soon as more information becomes available."
A WHO spokesman added: "WHO is currently in the process of obtaining further information to determine the public health implications of these two confirmed cases."
Professor Peter Openshaw, director of the Centre for Respiratory Infection at Imperial College London, said: "For now, we need to be watchful - any evidence of human-to-human transmission causing severe disease would be very worrying and would raise the spectre of a new Sars-like outbreak."