Health officials in Vietnam say a 23-year-old woman has tested positive for a deadly strain of bird flu.

This is the second human case of bird flu diagnosed in Vietnam this year.

Officials in northern Quand Ninh province say the woman became sick after eating chicken.  Hospital director Nguyen Quoc Hung says the woman has been under treatment for five days.

Last month, an eight-year old girl from northern Thanh Hoa province also tested positive for the H5N1 virus.

On Saturday, animal health authorities confirmed bird flu outbreaks in poultry in three provinces in Vietnam.

The H5N1 strain of avian influenza remains largely a virus in birds, but experts fear it could mutate into a form that is easily transmitted by humans.

The World Health Organization says bird flu has killed 248 people since it resurfaced in Asia in 2003.  More than 50 of the deaths have been in Vietnam.

Some information for this report was provided by AFP, AP and Reuters.