GUANGZHOU - Health authorities in south Guangdong province have yet to find the cause of the highly pathogenic H5N1 virus, commonly known as bird flu, that led to the death of a bus driver, a local disease control official said Sunday.

The 39-year-old man surnamed Chen in Bao'an district of Shenzhen was hospitalized for fever on December 21 and tested positive for the H5N1 avian influenza virus. He died of multiple organ failure Saturday afternoon, the Guangdong Health Department said in a statement.

The department also said that during the previous month prior to his fever, he had no direct contact with poultry and hadn't traveled out of the city.

Chen's wife said he had a habit of doing morning exercises every day near a wetland park and an artificial lake not far from his home, but "no proof has been found that his infection is connected with the migratory birds there," He Jianfeng, director of the Epidemics Studies Institute of the Guangdong Disease Control Center, said Sunday.

"We also don't know whether he had eaten poultry before he fell ill," He said.

He said contacts with poultry and migratory birds are two ways for humans to be infected with bird flu.

"But Chen had been in coma after being hospitalized, so we couldn't inquire about what birds or poultry he may have had contact with," he said.

The General Administration of Quality Supervision, Inspection and Quarantine (AQSIQ) on December 22  suspended supplies of live poultry to Hong Kong after a dead chicken tested positive in Hong Kong for the highly pathogenic H5N1 virus.

The AQSIQ said it would maintain close contact and work together with the Hong Kong Special Administrative Region (HKSAR) to jointly step up measures to control the epidemic.

The Guangdong Department of Agriculture announced Saturday that no epidemic of bird flu among poultry had been reported in the province.

Chen's wife said he had asked for sick leave and stayed at home five days before he was sent to hospital due to an ankle injury. While she prepared his dinners, she didn't know what he had been eating for lunch.

Hong Kong media reports have quoted one of Chen's friends as saying that Chen had slaughtered a chicken to cook for others, but He Jianfeng doesn't think that was the cause of his death.

"That took place a month ago. It cannot be the reason. The latent period of bird flu virus doesn't last that long," he said.

He advised locals against panicking, saying no proof has been found to show that bird flu virus can be spread among humans.

"By January 1, among the 120 people who had close contact with Chen, including his wife, colleagues and medical workers, no one has shown any symptoms," he added.

Also on Sunday, the Shenzhen Municipal Entry-Exit Inspection and Quarantine Bureau announced it had commenced 24-hour monitoring at all ports during the ongoing three-day New Year holiday to enhance health inspection of overseas visitors and guard against possible health incidents.