Healthcare workers in Indonesia are noticing that outbreaks of the deadly bird flu seem to come in family clusters, mostly affecting those linked by blood.

Indonesia is battling one of the worst outbreaks of the virus in the world, with four reported dead only in the last month, said USA Today.

Diana Ginting, head of a local health district office in Sumatra, where seven people died in May, told the newspaper, "No husbands and wives are infected; it's all brothers and sisters, mothers and children."

She and other health workers' suspicion that the spread of the disease is aided by a genetic component was supported last week in a report from the World Health Organization. In human-to-human transmission cases in Indonesia, the report found they occurred among those carrying the same genetic trait, USA Today reported.

Some experts fear up to 30 percent of poultry in Indonesia is infected by the deadly strain of the virus.

Battling the problem has been particularly difficult in Indonesia because it is so spread out, affecting vaccine availability.

Copyright 2006 by United Press International