SAN MARCOS -- San Marcos Mission Hills High School will be closed for two weeks, with extra-curricular activities cancelled, and siblings of students there are being asked to stay home as well, after a student from the high school was diagnosed with a probable case of swine flu, school and health officials said Saturday.

The closure is in accordance with a new U.S. Centers for Disease Control recommendation that when even one student at a K-12 school has a probable or confirmed case of the H1N1 virus, officials should consider closing the school for two weeks to preempt a wider outbreak.

Mission Hills High School, with about 2,500 students, is closed until May 18, but teachers will report for work during that time, San Marcos Unified School District Superintendent Kevin Holt said at a Saturday press conference.

San Diego County public health officer Wilma Wooten said lab results showed Friday that a San Marcos High School student was probably infected with the H1N1 influenza A virus. School and county officials decided it was in the interest of public health to follow the CDC guidelines.

"We want to err on the side of caution," Wooten said.

Two other schools in San Diego, San Diego School of Creative and Performing Arts in Paradise Hills and Kearny High School in Kearny Mesa, are also closed until May 18 because lab results show one student on each campus with a probable case of the virus.

Wooten said the CDC recommends the two-week closures because the H1N1 virus has great potential to spread among K-12 students. She said that children harbor and spread the virus longer than adults -- seven to 10 days after symptoms appear -- and students have plentiful and close social interactions that encourage the virus's spread.

"The closure of the school is a preventative measure to help prevent possible further infections," Wooten said.

No information was released on the San Marcos student believed to have the virus. Wooten said that the CDC will analyze a specimen from the student, and if the H1N1 virus is not confirmed, the school could reopen sooner.

Holt said siblings of students who attend Mission Hills are also being asked to stay home. While home from school, students should avoid friends and stay close to home, Wooten said.

"We don't want them going to the mall and congregating," she said.

The county health officer said that CDC guidelines for swine flu are changing constantly as more is learned about the disease. But currently, the guidelines do not recommend that teachers stay home unless they have symptoms of the illness, in part because they do not carry the virus as long as children.

"If faculty or teachers are well, they can continue in daily operations," Wooten said. "We've dismissed the students because they can be harbors or reservoirs of infection."

Both Holt and Wooten acknowledged that keeping children home would be a challenge for parents without child care, and suggested parents ask friends and neighbors for help.

Holt said janitors would clean the school thoroughly Monday, including washing desks and computer equipment with soap and water.

He said that Mission Hills High School teachers on Monday would probably start developing independent study lessons that students could get over the Internet or parents could pick up at the school.

"This isn't a vacation for kids," Holt said, while acknowledging that instruction could suffer with students at home.

The district will not lose state funding based on student attendance because of the closures, he said, adding that he did not anticipate any extra days would be added to the school year.

He said the district will work with the county and the state to reschedule Advanced Placement exams that were to start Monday.

Wooten said the county has 11 confirmed cases of the virus and 19 probable cases, with no new cases announced Saturday. She said patients' ages are from 3 to 54, all the cases have been mild, and none of those infected had recently travelled to Mexico.

The numbers do not include three Camp Pendleton Marines confirmed with the virus. Marine officials announced the base's third confirmed case Saturday, adding to two cases confirmed this week.

All three Marines are recovering, base officials said. They are in isolation and being treated as outpatients.

Riverside County health officials said Friday they had detected two more probable cases of swine flu, bringing the total number of suspected cases in that county to eight. No new cases were reported Saturday in the county.

One of the patients is a 60-year-old woman with an unknown travel history. No further information about her was available.

The other is a 21-year-old Wildomar woman with no recent trips to Mexico, health officials said. She did not need to be hospitalized.

Contact staff writer Sarah Gordon at (760) 740-3517 or sgordon@nctimes.com.

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