Authorities are racing to identify the cause of a mystery lung infection that has struck nearly 60 people in central China.
As of January 5 a total of 59 cases of unexplained pneumonia had been reported in Wuhan, a city with a population of roughly 11 million and the capital of Hubei province.
Seven people are in a serious condition after developing the infection, which triggers fever and breathing difficulties, authorities have said.
There were fears that the country was on the verge of a repeat epidemic of severe acute respiratory syndrome (SARS), which spread around the world in 2002-03, killing 700 people, after originating in China.
But the Wuhan Health Commission has confirmed that SARS is not the cause of the new infections - which are thought to have been contracted in late December in a local seafood market.
Middle East respiratory syndrome, influenza and avian flu have also been ruled out, but authorities are still scrambling to identify the source of the pneumonia outbreak.
“As of now, preliminary investigations have shown no clear evidence of human-to-human transmission and no medical staff infections,” the Wuhan Health Commission said in a statement on its website.
Over the weekend both Singapore and Hong Kong set up screening systems to check travellers arriving from Wuhan for a possible fever.
And while 15 travellers with pneumonia-like symptoms have been identified in Hong Kong, there is no evidence that they are infected with the same mystery illness.
The cases in Wuhan appear to be focused around the Huanan seafood market, where many of the patients are dealers or vendors. As well as seafood, the market - which has now been closed and disinfected - also trades in birds, pheasants, rabbits and snakes.
Ian Jones, professor of virology at the University of Reading, told The Telegraph that the infections may be linked to food poisoning.
“The link with the seafood market is pretty strong and can’t be ignored,” he said. “All of the epidemiological data points towards a single source as people have not gone on to infect others.”
Prof Jones added that seafood is a known source of a number of viral and bacterial infections and outbreaks of food poisoning from shellfish are relatively common.
“The complication here is that the symptoms are usually stomach upsets and sickness, not pneumonia, so it doesn’t quite fit,” he added. “My guess is, though, that the cause will be a variant of a standard shellfish associated virus.
“I don’t know why it’s given patients pneumonia - possibly the infection has triggered pneumonia as a secondary effect, not the primary one.
“But panic isn’t on the cards, and I think China is very well equipped to deal with it - they are almost a world leader in genomic sequencing. I wouldn’t expect the unknown to go on much longer - perhaps within a week of two we will have definitive news about what the disease is likely to be,” added Prof Jones.
A World Health Organization spokeswoman added that the agency is working closely with Chinese authorities to identify the source, with public health officials focusing investigations on the seafood market.
Protect yourself and your family by learning more about Global Health Security