WHO Raises Pandemic Threat Level of Swine Flu

Level four requires sustained human-to-human transmission able to cause what the WHO calls “community-level outbreaks.”


TORONTO, April 27 — The World Health Organization has raised its pandemic alert system to level four — sustained human-to-human transmission — in response to the swine flu outbreak in the U.S., Mexico, and at least two other countries.

The Geneva-based WHO made the change from level three — some human-to-human transmission — on the advice of an expert panel meeting today.

Earlier today, acting CDC director Richard Besser, M.D., said the change won’t affect the U.S. response to the outbreak.

“It really doesn’t matter from our perspective what you call this,” he said in a press conference. “Our actions are based on what’s happening in our country and our communities.”

Stepping up one phase, Dr. Besser said, “would not change anything that we are currently doing.”

The pandemic threat level has six major levels. Phases one through three increase from strictly animal-to-animal transmission to some human-to-human transmission, sufficient to create small clusters of disease.

Level four requires sustained human-to-human transmission able to cause what the WHO calls “community-level outbreaks.”

Levels five and six are the pandemic levels.

Phase five is characterized by human-to-human spread of the virus into at least two countries in a region, although most countries are not affected.

In phase six, there are community-level outbreaks in at least one other country in a different region. This level is regarded as a signal that a global pandemic is truly under way.

By Michael Smith, North American Correspondent, MedPage Today
Published: April 27, 2009

Source: MedPage Today

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