US authorities are to tell the World Health Organization (WHO) whether the new swine flu virus has spread significantly between humans within the country. If the spread is significant it may indicate the beginnings of a flu pandemic.

If it is confirmed that infected people from two countries are spreading the virus to their close contacts and family members in a sustained way, the WHO may then decide to raise the alert scale from 4 to 5. The scale can reach a maximum of 6. When the swine flu virus spread to Europe the pandemic alert level was raised from 3 to 4.

According to the CDC (Centers for Disease Control and Prevention, USA) people who were in contact with others who were confirmed cases of swine flu infection have developed flu-like symptoms themselves.

Who spokesman, Gregory Hartl, said that the World Health Organization is still awaiting final confirmation from the US authorities, but it appears that there are some cases in New York which appear to be person-to-person transmission. He added that "If we have a confirmation from the United States or Canada, we could move to phase 5."

There have been isolated cases of people catching swine flu from a pig - but infection stops there. The human does not go on to infect other humans. Even with bird flu, on very rare occasions, one person has infected another - and stopped there. This new swine flu H1N1 is not "just stopping there" - it seems to be moving on from person-to-person, to person…to person, etc.

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