Most of the students who have fallen ill attend Ocean Shore Elementary School, and there have been a few cases at Ortega Elementary School since the bug first surfaced on May 8, said Superintendent Wendy Tukloff.
A Monterey-area middle school sent 113 students home after a suspected norovirus outbreak, and county health officials are investigating the cause.
In the last two months, nearly 30 schools in Contra Costa County have seen outbreaks of the stomach virus this winter.
Principal Patrick Ruff said Monday that the bug hit more than 500 students and 70 faculty and staff altogether.
A San Francisco high school will now be closed through the weekend because of a stomach flu outbreak that has sickened dozens of students.
At least three athletic events involving St. Ignatius College Preparatory teams have been postponed following the closure of the school because of an outbreak of the stomach flu, West Catholic Athletic League officials said.
Saint Ignatius College Preparatory will be closed Wednesday for cleaning after nearly 200 students came down with the stomach flu.