CDC says virus lacks 'virulence' traits

Top health officials in the U.S. and abroad projected a cautious optimism that the new swine flu virus is not as lethal as initially feared. Genetic analysis has failed to detect in the influenza virus the "virulence factors" seen in the killer 1918 Spanish flu or the avian flu that surfaced earlier this decade, said Richard E. Besser, acting director of the Centers for Disease Control and Prevention. In addition, the new virus may have been more widespread in Mexico than originally reported, which would make the seemingly high mortality rate there a misperception, he added.