LONDON (AP) -- British officials say a mysterious virus related to SARS may have spread between humans, as they confirmed the 11th case worldwide of the new coronavirus in a patient who they say probably caught it from a family member.

The new virus was first identified last year in the Middle East and the 10 people who have previously been infected had all traveled to Qatar, Saudi Arabia, Jordan or Pakistan.

According to Britain's Health Protection Agency, the latest patient is a U.K. resident with no recent travel to any of those countries but who had close personal contact with an earlier case. The patient may also have been at greater risk of infection due to an underlying medical condition and is currently in intensive care at a Birmingham hospital.

"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," John Watson, head of the respiratory diseases department at the Health Protection Agency, said in a statement. "If (the) novel coronavirus were more infectious, we would have expected to have seen a larger number of cases."

Six hospital staffers where the patient is being treated are being monitored for infection but none have so far showed any symptoms of the illness. The patient did not come into contact with any other hospital patients and is currently being kept in isolation.

The new coronavirus is part of a family of viruses that cause ailments including the common cold and SARS. In 2003, a global outbreak of SARS killed about 800 people worldwide.

Officials at the World Health Organization said the new virus has probably already spread between humans in some instances. In Saudi Arabia last year, four members of the same family fell ill and two died. And in a cluster of about a dozen people in Jordan, the virus may have spread at a hospital's intensive care unit.

"We know that in some of those cases there was close physical contact between family members caring for one another, so we can't rule out human-to-human transmission," said Gregory Hartl, a WHO spokesman.

He said there were still big gaps in the understanding of the novel coronavirus, which can cause acute pneumonia and kidney failure. Of the 11 cases to date, five people have died.

Health experts still aren't sure how humans are being infected. The new coronavirus is most closely related to a bat virus and scientists are considering whether bats or other animals like goats or camels are a possible source of infection.

Michael Osterholm, an infectious diseases expert at the University of Minnesota, warned the virus could be adapting into a more transmissible form. "At any moment the fire hydrant of human-to-human transmission cases could open," he said. "This is definitely a 'stay tuned' moment." He noted that before SARS sparked a worldwide epidemic, there were a handful of human-to-human cases, until something happened, like a virus mutation, which triggered an explosion of cases.

WHO says the virus is probably more widespread than just the Middle East and has advised countries to test any people with unexplained pneumonia.

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