Chinese authorities are warning of a "very high" possibility of outbreaks of bird flu over the next several months as health officials hunt for clues how a father and son became infected with the virus.

Vice Agriculture Minister Yin Chengjie was quoted as saying Tuesday he is not optimistic about winter and spring months when the virus is at its most contagious.

Yin said it is critical to improve methods of poultry breeding, slaughter, delivery and processing in the country.

Meanwhile, Chinese health officials are trying to determine how a Chinese man from eastern Jiangsu province, whose son died from bird flu December 2, also contracted the virus. No bird flu outbreak has been reported among the province's wild birds or poultry.

The case is raising concerns of possible human to human transmission.

Scientists have been concerned the deadly H5N1 strain of the virus could change into a form easily passed among humans, sparking a pandemic.

The World Health Organization reports there have been at least 26 human cases of avian flu confirmed in China in recent years, 17 of them fatal.

Bird flu outbreaks were reported last month in Hong Kong, South Korea and Burma.

The WHO says more than 200 people have died of bird flu worldwide since the first outbreak in 2003.