Officials Backtrack Bird Flu Cluster

Johannes Ginting, left, the only remaining member of a family of eight which has been decimated by bird flu deaths, is assisted to eat by his wife Amnestia as he lies on a bed at a hospital in Medan, Indonesia, Thursday, May 25, 2006. The members of the family probably passed the disease among themselves, but health officials said there was no evidence the virus had mutated and decided against raising the pandemic alert level. (AP Photo/Binsar Bakkara) (Binsar Bakkara - AP)

Scientists are unsure how this has occurred, but they have theorized that the virus may pass from one person to another through droplets sneezed or coughed by humans into the air or food, onto surfaces or in some combination.

It has been suggested that some people may have a genetic susceptibility to the disease. In all four family clusters recorded so far, only direct blood relatives _ not spouses _ have caught bird flu.

Bjorge said the sick family members in Indonesia were in close physical proximity, which included sleeping close to each other.

"Even though so many people were tragically affected in this cases, it hasn't really changed the picture of avian influenza in Indonesia at this time," Bjorge said.

A top U.S. health official said Wednesday, however, that the Indonesian case may be the first time bird flu has been passed in a chain of transmission, with a person infected by a bird passing the virus to another person, who then went on to infect a third person or people.

Previous clusters all involved only one jump from person to person. Scientists are still investigating to see how many possible jumps the virus could have made in Indonesia.

Bird flu has killed 124 people worldwide, more than a quarter of them in Indonesia. Scientists fear the H5N1 virus will mutate into a highly contagious form, possibly sparking a global pandemic. So far, most human cases have been linked to infected birds.

WHO said it will leave its pandemic alert level unchanged at 3, where it has been for months, meaning there is "no or very limited human-to-human transmission."

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Associated Press reporters Sam Cage and Alexander G. Higgins in Geneva and Mike Stobbe in Atlanta, Georgia, contributed to this report.