Another person has died of a mysterious respiratory virus and three more cases have been discovered in Saudi Arabia and Qatar, the World Health Organisation said Friday.
"This brings the total of laboratory-confirmed cases to six," the Geneva-based UN agency said in a statement.
A Saudi man died from the novel coronavirus in June and a Qatari man was hospitalised in London with the virus after a trip to Saudi Arabia.
The WHO has previously confirmed that the new strain was part of the coronavirus family, which also includes the deadly SARS virus as well as the common cold.
What sets the new virus apart from SARS is that it causes rapid kidney failure, the WHO said.
In view of the small number of cases with little connection between them, the WHO has previously said the virus did not appear to be very contagious, but it stressed Friday that many cases might be going undetected.
The Geneva-based UN agency meanwhile said that only the two most recently confirmed cases in Saudi Arabia were so far seen as epidemiologically linked, since they were both from the "same family, living in the same household".
"Preliminary investigations indicate that these two cases presented with similar symptoms of illness. One died and the other recovered," the organisation said.
It noted however that two other members of the same family had presented similar symptoms—one of whom had died—but stressed that the person who lived had tested negative for the novel coronavirus while the test on the deceased was still pending.
In the new Qatari case, the patient had been sent to Germany in October for treatment at a special lung hospital and had recovered, Germany's national public health institute said in a statement.
The WHO called Friday on countries to "continue their surveillance for severe acute respiratory infections" in general, adding that it was working to provide guidance related specifically to the novel coronavirus.
"Until more information is available, it is prudent to consider that the virus is likely more widely distributed than just the two countries which have identified cases," it cautioned.
Countries "should consider testing of patients with unexplained pneumonias for the new coronavirus even in the absence of travel or other associations with the two affected countries," it said.
According to a study published by the journal of the American Society for Microbiology earlier this week, the mystery virus appears to be most closely linked to viruses found in bats.
"The virus is most closely related to viruses in bats found in Asia, and there are no human viruses closely related to it," Ron Fouchier of the Erasmus Medical Center in The Netherlands, who led the study, told the journal.
"Therefore, we speculate that it comes from an animal source," he added.
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