A Thai woman has tested positive for bird flu, senior health officials said on Monday, making her the 20th person to have caught the deadly disease since it hit the country two years ago.

"A 50-year-old woman is confirmed to have bird flu after all three lab tests showed positive results," Paijit Warachit, head of the Department of Medical Sciences, told Reuters.

"Her condition is improving and I believe she will be well soon," Paijit said.

Thirteen Thais have died of bird flu since the H5N1 virus struck in late 2003 and the woman was the third person to have caught bird flu in Thailand this year.

She was admitted to a Bangkok hospital on Saturday after telling her doctor she had been helping her husband clean up a farm where chicken were culled after laboratory tests showed they had the virus, another official said.

"We believe she would have caught it from fresh chicken droppings while she was sweeping," Disease Control Department chief Thawat Suntrajarn said.

The farm was in Nonthaburi, on the outskirts of Bangkok and one of six provinces hit by a fresh rash of bird flu outbreaks this year, officials said.

Her husband, still looking healthy, was being quarantined while awaiting test results, Thawat said.