A third patient in Britain has contracted a new SARS-like virus, becoming the second confirmed British case in a week and showing the deadly infection is being spread from person to person, health officials said on Wednesday.

The latest case, in a man from the same family as another patient, brings the worldwide number of confirmed infections with the new virus - known as novel coronavirus, or NCoV - to 11.Of those, five have died. Most of the infected lived or had recently been in the Middle East. Three have been diagnosed in Britain.NCoV was identified when the World Health Organisation (WHO) issued an international alert in September 2012 saying a virus previously unknown in humans had infected a Qatari man who had recently been in Saudi Arabia.

The virus belongs to the same family as SARS, or Severe Acute Respiratory Syndrome - a coronavirus that emerged in China in 2002 and killed about a tenth of the 8,000 people it infected worldwide. Symptoms common to both viruses include severe respiratory illness, fever, coughing and breathing difficulties.Britain's Health Protection Agency (HPA) said the latest patient, who is a UK resident and does not have any recent travel history, is in intensive care at a hospital in central England.

"Confirmed novel coronavirus infection in a person without travel history to the Middle East suggests that person-to-person transmission has occurred, and that it occurred in the UK," said John Watson, the HPA's head of respiratory diseases.He said the new case was a family member in close contact with another British case confirmed on Monday and who may have been at greater risk because of underlying health conditions.The WHO said although this latest case shows evidence of person-to-person transmission, it still believes "the risk of sustained person-to-person transmission appears to be very low".

RISK VERY LOW, BUT VIRUSES CAN MUTATE

Coronaviruses are typically spread like other respiratory infections such as flu, travelling in airborne droplets when an infected person coughs or sneezes.Yet since NCoV was identified in September, evidence of person-to-person transmission has been limited.Watson said the fact it probably had taken place in the latest two cases in Britain gave no reason for increased alarm."If novel coronavirus were more infectious, we would have expected to have seen a larger number of cases than we have seen since the first case was reported three months ago.

Tom Wilkinson, a senior lecturer in respiratory medicine at Britain's University of Southampton, said that if NCoV turned out to be like the previous SARS outbreak, it may prove quite slow to spread from one human to another."But it's early days to make any definite statements because viruses can change and mutate very rapidly, so what is right today may be wrong tomorrow," he told Reuters.Based on the current situation, the WHO said all member states should continue surveillance for severe acute respiratory infections and investigate any unusual patterns.

"Testing for the new coronavirus should be considered in patients with unexplained pneumonias, or in patients with unexplained severe, progressive or complicated respiratory illness not responding to treatment," it said in a statement.The WHO said on Monday that the confirmation of a new British case did not alter its risk assessment but "does indicate that the virus is persistent".The British patient confirmed on Monday had recently travelled to Saudi Arabia and Pakistan, and is in intensive care in a separate British hospital, the HPA said.

Among the 11 laboratory confirmed cases to date, five are in Saudi Arabia, with three deaths; two are in Jordan, where both patients died; three are in Britain, where all three are receiving treatment; and one was in Germany in a patient from Qatar who had since been discharged from medical care.The WHO said at this stage there is no need for travel or trade restrictions, or for special screening at border points.