The baby was not infected with the H5N1 bird flu virus but the latest case underscored intense unease in the crowded city over the threat from bird flu after H5N1 made the first known jump to humans in Hong Kong in 1997, killing six people.

The grandmother of the nine-month-old girl had taken her to a neighborhood wet market every day in the week before she fell ill, and a senior health official said on Tuesday the baby had probably contracted the H9N2 virus during these visits.

H9 viruses are commonly found in Hong Kong's live poultry markets, but humans have only been known to have been infected by them on two other occasions in the city. Two girls were infected in 1999 and a boy in 2003. All have since recovered.

Although the infant has also recovered, experts say the incident highlights the need to get rid of live poultry stalls in Hong Kong's wet markets - a fixture in most neighborhoods in the crowded city.

"The only gap in our defense against bird flu is the wet market. This shows humans can get infected in such a setting. Something must be done to the poultry stalls in our markets," said Lo Wing-lok, an infectious disease expert.

Abbatoir plan

Calls to replace live poultry stalls with a central abbatoir began as early as 1997 after H5N1 infected 18 people in Hong Kong and led to the mass culling of the city's poultry.

But resistance from business groups has stalled government plans to get a central abbatoir up and running by 2010.

"It won't be easy at all. We can't be sure that the facility will be built at all," Lo said.

Many experts are more concerned the H5N1 bird flu virus could start a pandemic and kill millions if it learns to spread efficiently among people. But no one can rule out the possibility that milder virus strains can turn nasty.

"The H9 virus itself is not a great concern because of its low pathogenicity ... (but) every virus has a pandemic potential. Not the virus per se, but it can be part of a reassortment. Together with another virus, the H9N2 can reassort and give rise to something with pandemic potential," said Lo.

Julian Tang, a virologist at the Chinese University, said: "Previous human H9 (H9N2) cases have only caused mild illness, so there is no historical reason to worry. If patients infected with H9 start dying, then we will take it more seriously.

"It is quite possible that H9 influenza viruses could evolve in the same way (like H5N1 did), but we just have not seen it yet, so people tend not to worry about it."