SAN MARCOS, Calif. -- Teachers at Mission Hills High are expected to return to campus Tuesday to work in teams to get assignments to their students while the San Marcos school is closed because of an outbreak of swine flu.

Mission Hills is one of three schools tentatively closed until May 18 because of cases of the H1N1 virus.

"It's creating a lot of issues we're trying to resolve," Principal Brad Lichtman told The North County Times.

Lichtman said important tests, sporting events, school funding and the semester calendar all could be affected because of the closure, which went into effect Monday, the Times reported.

Also closed are Kearny High School in Kearny Mesa and the School of Creative and Performing Arts in Paradise Hills.

On Monday, nine more people, including a San Diego State student who lives off-campus, were diagnosed with swine flu, bringing the county's total of confirmed cases to 24.

SDSU's campus daycare center was also closed after 20 children and three staff members reported flu-like symptoms but tests for swine flu have been negative, according to county public health officials. A decision on when to reopen the center was pending, according to university officials.