MARIN COUNTY (KCBS) — Health officials in Marin County report they are seeing an increase in the number of people contracting the swine flu virus which killed thousands of people worldwide in 2009.

The 2009 swine flu, also known as the H1N1 strain of influenza-A killed 18, 550 people, according to the World Health Organization. It arrived in U.S. and subsided until now.

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Ten Marin specimens that tested positive were sub-typed and all were identified as H1N1, which coincides with state and national testing results, county officials reported.

Dr. Robert Benjamin, Marin County’s interim deputy heath officer, said this time it’s younger people, more than the old, that are being affected.

“This particular strain is now occurring in a younger population that believes in its immortality and invincibility. And the reality is that folks who are not immunized and exposed can get quite ill,” he said.

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Children have not necessarily developed and immunity because the swine flu hasn’t been as prominent within the general population compared to other flu types. It can also be more debilitating and severe than other flu viruses.

In Southern California, a 28-year-old San Juan Capistrano woman, who had an underlying medical condition, died last week of H1N1, according to the Orange County’s Health Care Agency.

Benjamin said the best way to avoid it is to get a flu shot.

“The immunization this year is effective against this year’s strain of influenza—so go get it,” Benjamin said.

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