"There are six confirmations. One from Surabaya and five from Medan. One from Medan is still alive," said Sari Setiogi, the WHO's Indonesia spokeswoman.

Separately, Indonesia's health ministry said a 12-year-old boy died of bird flu four days ago in Jakarta's eastern suburb of Bekasi, according to local tests.

Blood samples have been sent to a WHO-affiliated laboratory in Hong Kong for confirmation, ministry spokeswoman Lily Sulistyowati said. Local tests are not considered definitive.

An outbreak of H5N1 bird flu involving about seven members of a family at Medan in North Sumatra province has worried health agencies around the world but a Health Ministry official said on Wednesday it was not a case of human-to-human transmission.

"The spread was through risk factors from poultry or other animals. There is no proof of human to human," Nyoman Kandun, director-general of disease control, told Reuters.

"The world is watching us. We are not being hasty," he added.

Four of the five family members have died. An eighth member of the family previously reported by the WHO to be part of the cluster of infections merely had a fever and is now not believed to have had bird flu.

The WHO has sent a team to the area near Medan. The agency said it was on alert for signs the virus is mutating into one that can be easily transmitted between people, a development that could signal the start of a pandemic in which millions could die.

Such a mutation could occur anywhere there is bird flu, the WHO says.

Asked about the possibility of a change in the virus and whether there had been human-to-human infection in Sumatra, WHO spokeswoman in Geneva Maria Cheng said: "It is too early to draw any conclusions. I have not heard any suggestion that the virus is any different," referring to the laboratory tests in Hong Kong.

Source unclear

She said local health authorities have told the WHO there is no evidence so far the virus has spread beyond the initial cluster -- which it might be expected to do if there were a mutation.

"They do not have cases of people who were connected to the family under observation or suspected of being infected."

The health ministry's Kandun said authorities were still trying to identify the source of the virus in the cluster case in Kubu Simbelang village in Karo regency, about 50 km (30 miles) south of Medan.

But an Indonesian agriculture official who declined to be named told Reuters tests had shed no light on the case.

"There is a big question mark. Blood samples from all kinds of animals from chickens, ducks, geese, birds, pigs, cats and dogs turned out negative so far. Manure has also been checked. The result is negative," the Jakarta-based official said.

Some reports have suggested chicken manure used as fertilizer might be the link. Infected birds can excrete large amounts of the H5N1 virus and this can be one way it can spread to birds, and people.

The sixth of the cases confirmed on Wednesday was a 38-year-old catering businesswoman from Surabaya who had dealt with live pigs and pork meat before she died last week.

The latest deaths bring the number of Indonesians who have died from bird flu to 30, by far the highest death rate in the world this year from the disease.

 Bird flu has killed 115 people worldwide, the majority in east Asia, since reappearing in 2003. Virtually all the victims caught the disease from poultry.

The H5N1 virus is endemic in much of Indonesia. On Tuesday a senior Agriculture Ministry official said H5N1 had been detected for the first time in poultry in remote eastern Papua province.

Source: Reuters