"This is the most significant development so far in terms of public health," said Peter Cordingley, spokesman for the West Pacific region of the WHO. "We can't find sick animals in this community and that worries us."
None of the poultry tested by a WHO team in the village of Kubu Sembelang in North Sumatra were infected by the H5N1 strain of bird flu, the virus that has spread among birds in Asia to parts of Europe and Africa and is responsible for over 120 human deaths, 33 of these in Indonesia.
"We're not surprised that there is possible human-to-human transmission," said Steven Bjorge, the WHO team leader in Kubu Sembelang. "The thing we're looking for is whether it's sustained beyond the immediate cluster."
Since the virus surfaced again in early 2003, health experts are watching closely for mutations that could cause it to become easily transmissible from one person to another. To date most infections are the result of direct contact with sick birds but there are isolated cases of very limited human-to-human infection.
The family deaths in Indonesia are still under investigation, but WHO spokeswoman Maria Cheng said that the virus has not mutated to the point of sparking a pandemic and said there are no plans to bring experts together to discuss raising the WHO's bird flu alert that has remained at phase three, where "a new influenza virus subtype is causing disease in humans, but is not yet spreading efficiently and sustainably among humans."
Of the seven members in the extended family, six have died, the most recent a 32-year-old male on Monday who developed symptoms on May 15 and is the brother of the woman believed to have contracted the disease first. She was a vegetable vendor in a market that sold live poultry.
Three of the confirmed cases spent the night in a small room with the woman when she was symptomatic and coughing, according to a statement on the WHO's Web site. Other cases live in adjacent houses and attended a family pork roast at the woman's house on April 29, two days after she became sick.
The man who died on Monday is believed to have caught the flu while caring for his 10-year-old son who died May 13.
Residents of Kubu Sembelang who had contact with the family have been quarantined or have been treated with Tamiflu, an antiviral drug. Local authorities have resisted working with outside health experts, according to WHO officials.
The WHO investigation has found no indication that the virus spread outside the extended family, and Bjorge said that the virus that infected the family was genetically the same as an earlier virus circulating earlier among poultry in North Sumatra.
The H5N1 strain has spread from Asia to infect birds in 54 countries and humans in 10. The most recent outbreak occurred in China where officials confirmed on Wednesday an outbreak among wild birds in the remote far-western Qinghai province in Tibet.
