HANOI, Aug 15 (Reuters) - Vietnam has detected a bird flu outbreak in the northern province of Cao Bang bordering China, the country"e;s second infection among poultry so far this month, the Agriculture Ministry said on Wednesday.

Eighty-nine chickens and ducks died at a farm last Saturday and tests in Hanoi have confirmed they were infected by the H5N1 virus, the ministry"e;s Animal Health Department said in a report.

The infected farm is in Thach An district, about 70 km (43 miles) south of the border with China"e;s province of Guangxi.

The previous poultry outbreak was detected on Aug. 2 in the northwestern province of Dien Bien, which -- along with Cao Bang and the southern province of Dong Thap -- remains on the government"e;s watchlist for bird flu infection.

Bird flu has infected seven people in Vietnam so far this year, four of whom have died, bringing the death toll from 100 confirmed infections since late 2003 to 46, the Health Ministry said.

Early this month a 15-year-old boy from the northern province of Thanh Hoa died from bird flu while en route to a Hanoi hospital.

Globally, the H5N1 virus has killed 193 people out of 320 known cases, according to a tally of the World Health Organisation. Hundreds of millions of birds have died or been slaughtered.

The H5N1 virus remains mainly a virus of birds, but experts fear it could mutate into a form easily transmitted from person to person and sweep the world, killing millions.