A mysterious new respiratory virus that originated in the Middle East spreads easily between people and appears more deadly than Sars, doctors have reported after investigating the biggest outbreak in Saudi Arabia.
More than 60 cases of what is now called Mers, including 38 deaths, have been recorded by the World Health Organisation (WHO) in the past year, mostly in Saudi Arabia.
So far, illnesses have not spread as quickly as Sars did in 2003, ultimately triggering a global outbreak that killed about 800 people.
An international team of doctors who investigated nearly two dozen cases in eastern Saudi Arabia found the new coronavirus has some striking similarities to Sars, but scientists remain baffled about the source of Mers (Middle East respiratory syndrome).
In a worrying finding, the team said Mers not only spreads easily between people, but within hospitals. That was also the case with Sars, a distant relative of the new virus.
"To me, this felt a lot like Sars did," said Trish Perl, a senior hospital epidemiologist at Johns Hopkins Medicine, who was part of the team. Their report was published online in the New England Journal of Medicine.
Dr Perl said they could not nail down how it was spread in every case - through droplets from sneezing or coughing, or a more indirect route. Some of the hospital patients were not close to the infected person, but somehow picked up the virus. "In the right circumstances, the spread could be explosive," said Dr Perl, while emphasising that the team only had a snapshot of one Mers cluster in Saudi Arabia.
Cases have also been reported in Jordan, Qatar, the United Arab Emirates, Britain, France, Germany, Italy and Tunisia. Most have had a direct connection to the Middle East.
In the Saudi cluster, certain patients infected many more people than would be expected, Dr Perl said. One patient who was receiving dialysis treatment spread Mers to seven others, including fellow dialysis patients at the same hospital. During Sars, such patients were known as "superspreaders" and effectively seeded outbreaks in numerous countries.
Dr Perl and colleagues also concluded that symptoms of both diseases are similar, with an initial fever and cough that can last for a few days before pneumonia develops. But Mers appears far more lethal. Compared to Sars' 8% death rate, the fatality rate for Mers in the Saudi outbreak was about 65%, though the experts could be missing mild cases that might skew the figures.