CDC officials described the virus as having a unique combination of gene
segments not seen in people or pigs before. The bug contains human
virus, avian virus from North America and pig viruses from North
America, Europe and Asia.
Suspicions that the fatal outbreaks of flu in Mexico were not of the
normal seasonal influenza arose because most cases were in healthy
young adults, WHO spokesman Gregory Hartl said.
"Because these cases are not happening in the very old or the very
young, which is normal with seasonal influenza, this is an unusual
event and a cause for heightened concern," Hartl said in an interview
with Canadian broadcaster CBC.