Ninety percent of the people infected with bird flu have been under the age of 40, and 60 percent of them have died, according to the latest analysis from the World Health Organization.
But the WHO researchers stressed their analysis did not suggest why this might be and noted there are several theories on why the H5N1 virus seems to attack younger people.
The H5N1 avian influenza virus has infected 272 people in 10 countries since it re-emerged in 2003. It has killed 166 of them.
It remains mostly a virus of birds and has killed or forced the culling of more than 200 million chickens, ducks, geese, turkeys and other fowl.
But its occasional attack on a human being has researchers worried. They fear it could mutate into a form more like seasonal flu, in which case it would be spread around the world by people and could kill millions.
So WHO is watching it very carefully and keeping statistics on every case. This kind of work, called epidemiology, can help scientists understand diseases, who they infect and who is most in danger.
WHO's Weekly Epidemiological Record, published on its Web site at www.who.int, analyzes all laboratory-confirmed human cases of H5N1 infection reported between late November 2003 and late November 2006.
The analysis said the median age of people confirmed infected was 18 years old.
Source: Bio-Bio Technology