A Chinese bus driver who tested positive for the H5N1 bird flu virus died in a city bordering Hong Kong today, health officials said. It was the country's first reported case of the disease in humans in 18 months. The man surnamed Chen died in the wealthy southern city of Shenzhen, provincial health officials said. Shenzhen is separated by a small river from Hong Kong, where thousands of birds have been slaughtered after two were confirmed to have the virus last week. During the month prior to his fever, the 39-year-old had apparently had no direct contact with poultry and did not travel out of Shenzhen, a metropolis of 10 million people. H5N1 rarely infects humans and usually only those who come into close contact with diseased poultry. But among those infected, nearly 60% die, and scientists are closely watching the virus for any signs it is becoming more easily transmissible from human to human. Chen developed a fever on December 21 and was admitted to hospital on December 25, city and provincial authorities said in a statement. Health Ministry experts confirmed today that he was infected with H5N1, the provincial health department said.