HANOI, Vietnam — Vietnam confirmed its first human bird flu case in a year and a half Wednesday, as the virus continues to spread through the country's poultry stocks.

A 30-year-old man from northern Vinh Phuc province remains in hospital and breathing through a respirator after testing positive for the H5N1 virus three days ago, said Tran Quy, director of Bach Mai hospital in Hanoi. "The man is in critical condition," he said.

"He has a high fever, difficulty breathing, coughing and the X-ray of his lung was completely white. All these are typical bird flu symptoms."

Quy said the man was admitted to the hospital last week. Relatives said he had helped prepare chickens for a wedding reception before falling ill.

It is the country's first human infection of H5N1 since November 2005 and comes as bird flu outbreaks among poultry have been reported in southern, central and northern Vietnam.

Samples of the virus will be shipped to a World Health Organization lab for analysis and reconfirmation, said WHO country representative Hans Troedsson.

"We are following up with the Ministry of Health about it to get more details," he said.

"Since we know there is a risk for transmission to people, it's not really a surprise. It could just be one isolated case."

Vietnam had been hailed a success story for beating back the virus that began ravaging Asian poultry stocks in late 2003. A national mass poultry vaccination program, coupled with strong political will, brought the virus under control after it killed 42 people in the country. No poultry outbreaks were reported in 2006 but the virus flared again early this year.

The H5N1 virus remains hard for people to catch but experts fear it could mutate into a form that spreads easily among people. It has killed up to 185 people worldwide, WHO said.