Bird flu may have become more virulent

China on Thursday confirmed its 19th human case of bird flu, a 31-year-old man from the southern economic boom town of Shenzhen, bordering Hong Kong, who is critically ill in hospital.

Health Secretary York Chow said he was particularly worried about the latest H5N1 infection as it had occurred in a city-dweller with no history of close or prolonged contact with poultry.

The fact that the infection occurred in the summer, rather than the winter like most other outbreaks, was a further cause for concern, Chow said.

"We have a suspicion, but we have not confirmed it yet, that the virus might have become more virulent and more widespread than we have expected. If that is the case, the risk for humans to be infected in future is higher," he warned.

Humans are believed to contract the virus mainly from direct contact with infected animals. Scientists fear a global pandemic if the virus mutates and becomes easily transmissible between humans.

Chow said the authorities would continue to monitor the situation for similar cases, warning there might be more outbreaks among poultry and human infections in the coming winter.

The patient, a truck driver who remained critical in hospital, came down with fever and pneumonia-like symptoms on June 3. Test results released on Thursday confirmed the potentially deadly H5N1 strain of bird flu.

Investigation found he visited a local market, where live poultry was sold, several times before he became ill. None of the people who were in close contact with him had shown any symptoms, the authorities said.

He was the 19th human to have contracted the strain in China. Twelve of those cases have been fatal.

Hong Kong has been particularly concerned about the case in Shenzhen as thousands of people cross the border daily from Shenzhen and Guangdong province.

The Hong Kong government said it was maintaining temperature screening at immigration for all arrivals, with customs stepping up surveillance to combat smuggling of poultry into the territory.

Hong Kong was the scene of the world's first reported major bird-flu outbreak among humans in 1997, when six people died and more than two million poultry were culled.

But the southern Chinese territory has remained free of bird flu since early 2003 with stringent border control and reduction of the number of poultry imports from China.

More than 120 people worldwide have died from bird flu since it re-emerged as a threat in 2003, with most of the victims in Asia.