"Certainly this is the largest cluster we have in humans," said Dick Thompson, a WHO official who arrived in Indonesia Wednesday to join the seven-member team. "There's a suggestion of human-to-human transmission, and that is worrying."

He said UN investigators would study the travels of the Indonesian family over the last month to see whether they had visited places like markets that had put them at risk, or whether they might have passed the disease on to others. "It would probably take a while to decide whether human-to-human transmission had occurred," he said.

One family member got sick, died and was buried without being tested. She is believed to have infected six relatives, all confirmed to have had bird flu and died.

Dr. Julie L. Gerberding, of the U.S. Centers for Disease Control and Prevention in Atlanta said, "the leading hypothesis" right now is that the disease spread among family members after extremely close contact with ill relatives.

But International health officials emphasized that laboratory tests from the family did not suggest that the H5N1 bird flu virus had mutated in any way that would allow it to spread among humans more readily.

Some 27 out of 33 provinces in Indonesia have been contracted with bird flu, while human fatality stands at 32 and infections at 43, according to the WHO.

All over the world, the WHO has raised the confirmed human death toll from the H5N1 bird flu strain to 122, while the total number of confirmed human infections since the current outbreak began in 2003 has reached 216. Enditem

(Agencies)