The rapid spread of so-called "swine flu" among local school children shows that the virus is not fading away, a top regional health official said Thursday.

The rapid spread of so-called “swine flu” among local school children shows that the virus is not fading away, a top regional health official said Thursday.

“We’re not out of the woods at all,” said Dr. Jeff Duchin, chief of epidemiology for Public Health — Seattle and King County.

Nearly 70 percent of the confirmed cases in King County are in children between the ages of 5 and 18, Duchin told a special meeting of the King County Board of Health.

Confirmed cases are “only the tip of the iceberg” in terms of the total number of infections. Area emergency rooms also are reporting increasing numbers of sick children, he said.

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The levels of infection in school-aged children seem to be slightly higher than during a normal flu season, Duchin said. Most of the illnesses are mild, though 11 school-aged children were hospitalized.

The virus is largely sparing people over the age of 60, perhaps because previous exposure to a similar bug conferred some immunity.

But in children who have never seen anything like this virus, the course of the illness and the infectious period are longer than with an ordinary flu strain, Duchin said. And that appears to be contributing to the bug’s spread, as sick children circulate instead of staying home for at least a week.

“School nurses are telling us some kids are coming to school ill,” Duchin said. Some children that were out sick are returning to school before their symptoms are gone.

“That is putting other people … at risk,” Duchin said. “We are encouraging parents to take this seriously.”

The hardest hit school is Lindbergh High School in Renton, where nearly 400 students were out or sent home with flu-like symptoms on Tuesday and Wednesday. The school remains open. On Thursday, the number of absences had dropped below 300.

None of the students who are currently sick have yet been tested for the new flu variety, technically known as A (H1N1), Duchin said. Testing has mostly focused on the sickest people — those who wind up in the hospital — and none of the students have been that ill.

The health department is working with the school district to identify and test some of the sick students, said Duchin, who expects that many are infected with the new flu strain.

The flu spread quickly through several schools in New York City recently, leading to closures.

“We want to reduce that possibility here by doing everything possible to keep sick kids and staff out of school and child cares,” said Public Health Director Dr. David Fleming.

At least 75 King County schools and 12 school districts have had confirmed cases of the A (H1N1) flu.

As of Wednesday, there were 344 confirmed cases in King County, at least 20 of which resulted in hospitalization. There have been 107 cases in Snohomish County and 27 in Pierce. Statewide, the tally of confirmed cases is 516.

Public Health recommends that children with flu-like symptoms, including fever and cough or sore throat, stay home for seven days. If symptoms persist beyond that, they should stay home at least 24 hours after their symptoms are gone.

Sandi Doughton: 206-464-2491 or