The overwhelming majority of cases and deaths have been reported in Mexico and the United States, but increasingly the virus is spreading from person to person in countries as far apart as Britain, Spain, Japan, Chile and Australia.
"We still are waiting for evidence of really widespread community activity in these countries, and so it's fair to say that they are in transition and are not quite there yet, which is why we are not in phase 6 yet," Fukuda said.
Phase 6 is the highest alert on WHO's scale, signaling a pandemic - a global epidemic. In terms of the geographic spread of swine flu, the world is "at phase 5 but getting closer to phase 6," Fukuda said.
WHO is now debating whether to add a second measure that indicates how dangerous the virus is - rather than just how widespread - after several countries raised concerns that declaring a global pandemic could cause mass confusion and panic even though it is still unclear how dangerous the virus will be.
Some nations have already imposed costly trade and travel barriers, "drastic actions" that Fukuda said WHO would seek to prevent.
The agency is calling the situation "moderate" rather than "mild" while it waits to see how the outbreak develops.
Some experts have reported patients with symptoms different from those expected in this type of flu and the virus is causing severe infections in healthy, young adults.
"So we do have some hesitation in calling such an infection mild," Fukuda said. "It's probably fair to call the situation something like moderate right now."
RELATED INFORMATION:
FAQs about swine flu
Additional swine flu resources
Transcript of 6abc.com's swine flu chat with local experts
RELATED LINKS:
CDC Swine Flu site
World Health Organization
RELATED INTERACTIVE:
Swine flu cases around the world
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