The Health Protection Agency has confirmed another UK case of the Sars-like coronavirus, this time in Birmingham.
The HPA said a relative of a person who had been diagnosed with the disease in Manchester was being treated in Birmingham's Queen Elizabeth Hospital.
In total, there have been 11 confirmed cases globally including five deaths.
Three of the five victims have died in Saudi Arabia, while the other two have been killed in Jordan.
One person has been diagnosed with the disease in Germany and three people are still receiving treatment for the respiratory virus in the UK.
The person infected earlier this week contracted the virus while travelling in the Middle East. Their relative had not been travelling before contracting the disease, demonstrating that it has been transmitted person-to-person.
All of the previous cases involved people who either lived in or had travelled to the Middle East.
John Watson, head of the respiratory diseases department at the HPA, said: "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.
Risk of infection low
"This case is a family member who was in close personal contact with the earlier case and who may have been at greater risk of acquiring an infection because of their underlying health condition.
"To date, evidence of person-to-person transmission has been limited. Although this case provides strong evidence for person-to-person transmission, the risk of infection in most circumstances is still considered to be very low.
"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.
"However, this new development does justify the measures that were immediately put into place to prevent any further spread of infection and to identify and follow up contacts of known cases."
Watson added that the risk of novel coronavirus to the general population is very low, and that the HPA is continuing to work with national and international health authorities.
No travel restrictions have been put in place but people who present symptoms within 10 days of visiting the Arabian Peninsula and surrounding countries should seek medical advice, he said.
Symptoms include fever, coughing, shortness of breath and breathing difficulties.