A drought in northern China that has limited drinking water to almost 4 million people may also be making birds more susceptible to the deadly H5N1 avian-flu strain.

The lack of rainfall in Shandong, Shaanxi and other northern provinces since October causes stress for local fowl, said Hong Kong Veterinary Association President Veronica Leong, who specializes in birds. "Any sort of stress would make birds more susceptible to disease," she said by e-mail today.

Bird flu killed five people in China last month, three of whom were from regions experiencing drought. Lo Wing-Lok, a health adviser to the Hong Kong government, said yesterday China has an outbreak of bird flu among poultry that its government hasn't reported.

"As drinking water becomes more scarce for wild birds, they may come into closer contact with domestic fowl, increasing chances of cross-infection," said Nie Ben, agricultural commodities manager at Shanghai Continent Futures Co. in Dalian.

The Chinese government last week reported the nation's fifth bird flu death in 2009. The deaths were in the provinces of Shandong, Hunan, Guangxi, the municipality of Beijing and the Xinjiang autonomous region. Shandong, Xinjiang and Beijing have droughts.

About 3.7 million people and 1.85 million big animals have limited access to drinking water in northern China, the Ministry of Water Resources said on its Web site yesterday. Reduced soil moisture affected an estimated 9.7 million hectares of crops, it said.

Deng Haihua, director of the Ministry of Health's news department, declined to comment. The Ministry of Agriculture didn't respond to faxed questions about bird flu.

Hong Kong's government has found 18 dead birds on Lantau Island, three testing positive for the H5 strain of avian flu. Further testing is required to determine whether they carried the H5N1 strain, which can kill humans.

The city's Agriculture, Fisheries and Conservation Department said it's working with Chinese authorities to determine whether the dead birds washed ashore on Lantau from the mainland.

"There's no doubt of an outbreak of bird flu in China, though the government hasn't admitted it," Lo, the Hong Kong health adviser, said in an interview yesterday.

Health and disease tolerance determine how easily illness can spread between birds, said the veterinary association's Leong. A drought "does not mean that it would be automatically easier for disease to travel from one bird to another bird," she said.

China has said eight people have been infected by bird flu this year, including those killed by the disease. A three-year- old girl in Shanxi province infected by the H5N1 strain was discharged from a local hospital yesterday, making her the youngest person in China to survive an infection, the Ministry of Health said today.

Gong Guifen, director of the poultry division at the China Animal Agriculture Association in Beijing, said there are no direct links between drought and cases of bird flu.

"Poultry birds are more susceptible to viruses when the weather is cold or when living conditions are dense," she said. "But this winter hasn't been that cold."