The U.S. Centers for Disease Control has sought to allay fears stemming from the accidental distribution of a deadly flu virus to thousands of laboratories in 18 countries.

In the late 1950s, a deadly strain of the influenza virus triggered an Asian pandemic that killed as many as four million people.

Julie Gerberding (file photo)

But, according to Julie Gerberding, who heads the Atlanta-based Centers for Disease Control, no infections have been recorded in the United States stemming from samples of the virus, known as H2N2, inadvertently sent in testing kits to laboratories on four continents.

"There is no evidence that any person has acquired H2N2, and most of these laboratories have already destroyed their proficiency test panels. But we are ensuring that all steps are taken to identify every lab that may have the virus, and that it is quickly destroyed. We are doing everything we can, without taking any chances that this virus could infect an individual or spread to the public at large," she said.

The CDC says it is contacting all laboratories that received the virus samples and providing instructions on how to safely destroy them. Earlier, the World Health Organization ordered laboratories around the world to eliminate the samples, which were provided by the College of American Pathologists, a U.S. organization.

Such samples are routinely used by laboratories to test their detection capability - but with a more benign microbe. A spokesman for the College of American Pathologists has expressed regret and said the group would never have intentionally distributed the H2N2 virus.

White House spokesman Scott McClellan says resolving the situation is a high priority, and that no chances should be taken in dealing with the virus.