Health officials have confirmed that bird flu has killed six members of a single family in rural Indonesia, and doctors have tried to determine whether the virus was passed from person to person.
However, the World Health Organization is not elevating its pandemic alert level, even after suspicion that family members passed the disease between each other rather than catching it from poultry infected with the virus.
Right now, health officials are talking to locals and testing animals to find out how the strain of the avian flu virus known as the H5N1 was transmitted.
"It has all the earmarks, frankly, of human-to-human transmission," said Dr. William Schaffer, an epidemiologist and a specialist in infectious diseases at Vanderbilt University, but "in a very close, tight circumstance where there was very intensive exposure."
All the victims (seven have died, although one family member's cause of death was undetermined) were from one village from an extended family, and the transmission has all the earmarks of human-to-human transmission, according to WHO. But the agency is also quick to point out there is no evidence the virus has mutated into a form that could lead to a global pandemic. Plus, all these latest victims did live in close proximity to live poultry.
More information is needed -- and all the answers may be hard to come by, said Dr. Pascal James Imperato, director of the public health program at SUNY Downstate Medical Center in Brooklyn.
"Even such an investigation might not clarify matters much, because there were obviously other possible sources of infection than exposure to an infected person," Imperato said.
Retired vaccine expert Dr. David Fedsen noted that the family cluster, for now, doesn't seem to be all that alarming.
"If the virus that has affected this family had been a true pandemic virus, it would have spread throughout the neighborhood, into the community and into adjacent and even far-distant communities," he said. But one thing is clear: This is the biggest and most concentrated cluster of victims ever seen.
Each case of bird flu -- especially in a cluster such as this one -- adds fuel to the theory that there is a genetic trait that makes some people more likely to get the virus than others. Often in cluster cases, blood relatives will contract the virus while spouses or close friends do not, according to officials.
"The virus is the same poultry virus we are familiar with," Schaffer said. "It has not mutated. This is not a new strain, but this is the largest cluster of cases health officials have ever dealt with."
ABC News' Mark Litke and Gloria Riviera contributed to this report.