Health officials are trying to find out how a new strain of bird flu is infecting people in China — more than half of patients have had no contact with poultry.
By late last week, 87 people, mostly in eastern China, have contracted the H7N9 virus, and 17 had died. It is not clear how people are becoming infected, but the World Health Organization says there is no evidence of the most worrying scenario — sustained transmission between people.
“This is still an animal virus that occasionally infects humans,” said WHO official Michael O’Leary, “With rare exceptions, we know that people are not getting sick from other people.”
Experts say it may be premature to definitely rule in or out whether people sick with the virus have been in contact with poultry, and note that contact with wild birds is even more difficult to establish.
A study published last week showed the H7N9 strain is a so-called “triple reassortant” virus with a mixture of genes from three other flu strains found in birds in Asia. One of those three strains is thought to have come from a brambling, a type of small wild bird.
“We also know that, perhaps with rare exceptions, people are not getting sick from other people,” said Glenn Thomas, another WHO official.
British influenza expert Wendy Barclay said it’s hard to absolutely rule out exposure to poultry.
“The incubation time might be quite long, so visiting a market even 14 days before might have resulted in infection,” she said.
Chinese authorities have slaughtered thousands of birds and closed some live poultry markets to try to slow the rate of human infection. China’s poultry sector has recorded losses of more than 10 billion yuan ($1.6 billion) since reports of the strain emerged in early April.