* Still no clear pointer to source of infection in humans
* More than half of those infected had no contact with
* Little sign of sustained human-to-human infection
* International experts visiting markets and hospitals
(Recasts adding Chinese president, WHO quotes, expert comment)
By Megha Rajagopalan and Kate Kelland
BEIJING/LONDON, April 19 Health officials raised
further questions on Friday about the source of a new strain of
bird flu infecting humans in China after data indicated that
more than half of patients had had no contact with poultry.
The H7N9 virus has been found in 87 people, mostly in
eastern China, and killed 17. But it is not clear how people are
becoming infected and the World Health Organisation (WHO) says
there is no evidence of the most worrying scenario - sustained
transmission between people.
The WHO's China representative, Michael O'Leary, issued data
on Friday showing that half of the cases analysed had had no
known contact with poultry, the most obvious potential source,
but he said it appeared human-to-human transmission was rare.
"This is still an animal virus that occasionally infects
humans," he said. "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 scientific study published last week showed the H7N9
strain was 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.
Ian Jones, a virologist and flu expert at Britain's Reading
University, said none of the data or scientific analyses
available so far have been able to pin down the exact source of
the human infection or the route of transmission.
"Those are the things we need to know about," he said.
An international team of epidemiologists and other experts
led by the WHO and Chinese government officials will visit live
chicken markets and hospitals over the next several days in
Beijing and Shanghai.
Some bird samples have tested positive and China has culled
thousands of birds and shut down some live poultry markets.
A WHO spokesman in Geneva, Glenn Thomas, said that "evidence
suggests that poultry is a vehicle of transmission, but
epidemiologists haven't yet been able to establish a strong and
"We also know that, perhaps with rare exceptions, people are
not getting sick from other people."
The official China Daily newspaper quoted an investigator at
the Chinese Academy of Sciences as saying the H7N9 outbreak may
linked to the migration of wild birds.
"The infection time and route coincided with the migration
of water birds," He Hongxuan told the newspaper.
Chinese President Xi Jinping on Friday called for efforts to
strictly control sources of infection, boost checks of live
poultry and release accurate information.
He said researchers should work to accelerate development of
vaccines while local authorities should strengthen disease
control, according to a statement released by the Central
Committee of the Chinese Communist Party, of which he is the
China has warned that there could be more infections to
come. Many of the 87 cases, and 11 of the deaths, have occurred
in the commercial hub of Shanghai.
China's poultry sector has recorded losses of more than 10
billion yuan ($1.6 billion) since reports of the new flu
surfaced two weeks ago, an industry official said this
(Additional reporting by Terril Yue Jones in Beijing and
Stephanie Nebehay in Geneva; Editing by Kevin Liffey)