(CNN) -- A 39-year-old man in a southern Chinese hospital is suffering from what appears to be a contagious strain of avian flu, state media reported Friday.
The man -- identified by Xinhua as a bus driver with the surname Chen -- was hospitalized in Shenzhen on December 21 as he battled a fever. He tested positive for the H5N1 avian influenza virus, a provincial health department said Friday, according to the official news agency.
Chen was in critical condition Friday at the hospital, the health department said.
The man had not traveled out of the city of Shenzhen, nor did he have direct contact with poultry in the month before he came down with the fever, according to the department.
Shenzhen borders Hong Kong, where more than 17,000 chickens were ordered culled on the same day that Chen was hospitalized. That decision came after a chicken carcass tested positive for avian flu.
The territory's director of Agriculture, Fisheries & Conservation declared the Cheung Sha Wan Temporary Wholesale Poultry Market an infected place, the government said then in a statement.
Farmers were told they could not send chickens to the market for 21 days.
The Hong Kong government said it was working to trace the origin of the chicken, which was infected with the H5N1 avian influenza virus. But, as of December 21, authorities did not know the source.
As of December 15, the World Health Organization calculated that 573 people had been infected -- and 336 had died -- after coming down with the H5N1 avian influenza virus since 2003. Twenty-six of those deaths had been in China, with the largest number of fatalities, 150, occurring in Indonesia. Vietnam and Egypt had more than 50 deaths each.
This summer, the United Nations warned of a possible resurgence of the virus -- which peaked in 2006, at one point infecting people in 63 countries -- saying there are indications a mutant strain may be spreading in Asia.
A variant strain of H5N1 -- which can apparently bypass the defenses of current vaccines -- had appeared as of late August in Vietnam and China, reported the Food and Agriculture Organization of the United Nations.
The group noted that the strain's movement around Vietnam threatened Thailand, Malaysia, Cambodia, Japan and the Korean peninsula. By then, eight people in Cambodia alone had died this year after becoming infected this year, the agency added.
In addition to the health impact, the avian flu outbreaks have also come at a steep economic cost -- with the United Nations estimating earlier this year that it had contributed to the killing of over 400 million poultry and caused losses estimated at $20 billion.