A 21-year-old Indonesian woman, the sister of a boy who died of bird flu earlier this month, is suffering from the same disease, the health ministry said on Friday.

The patient, currently being treated at a hospital in East Java province, had contact with sick and dead fowl, as had her brother, said Runizar Ruesin, the head of the ministry´s bird flu information center.

"She has been declared a bird flu positive case by the ministry lab and NAMRU," he told Reuters, referring to a U.S. Naval Medical Research Unit based in Jakarta.

The Soetomo hospital in East Java capital Surabaya said the woman was also suffering from pneumonia.

"Her condition is stable but her pneumonia has not improved yet. She is still being supported by a respirator," Urip Murtejo, the hospital´s deputy director, told Reuters.

The H5N1 virus mainly affects birds but experts fear it could mutate into a strain capable of killing millions of people in a global pandemic.

Indonesia has become one of the frontlines in the battle against the disease. So far, 52 people have died of bird flu, the highest of any country, with the majority of deaths since the beginning of this year.

More deaths are feared because the virus is endemic in poultry across much of the complex archipelago of 17,000 islands, home to multitudes of different cultures and languages.

The government has also been reluctant to carry out mass culls of infected poultry, citing logistical problems, lack of donor cash and resistance by many farmers to accepting limited compensation for culled fowl.

More than 500 chickens have been culled by the government around the siblings´ hometown of Tulungagung since the boy died to contain the virus.