UPDATE 1-'Something different" happening with new flu - CDC

(Updates throughout with quotes, details; changes dateline from Chicago)

*Up to 7 percent of population sick in heavily hit areas

*Flu season could last all year this year in US

By Maggie Fox, Health and Science Editor

WASHINGTON, June 18 (Reuters) - The new strain of H1N1 flu is causing "something different" to happen in the United States this year -- perhaps an extended year-round flu season that disproportionately hits young people, health officials said on Thursday.

An unusually cool late spring may be helping keep the infection going in the U.S. Northeast, especially densely populated areas in New York and Massachusetts, the officials at the U.S. Centers for Disease Control and Prevention said.

And infections among healthcare workers suggest that people are showing up at work sick -- meaning that workplace policies may be contributing to its spread, the CDC officials said.

The new strain of swine flu is officially a pandemic now, according to the World Health Organization.

So far the virus is causing mild to moderate disease, but it has killed at least 167 people and been confirmed in nearly 40,000 globally.