The government issued new guidance for schools with confirmed cases, saying they should close for at least 14 days because children can be contagious for seven to 10 days from when they get sick. That means parents can expect to have children at home for longer than previously thought.

The Education Department said that 433 schools had closed, affecting 245,000 children in 17 states. That was about 100 more schools reported closed than reported on Thursday.

Major U.S. airlines, meanwhile, announced plans to curtail flights into flu-ravaged Mexico.

Nearly 300 schools nationwide were closed yesterday to avoid the spread of swine flu, and education and health officials in the Washington area and elsewhere were working in tandem to reassure worried parents and weigh whether more campuses should be shuttered.

The bulk of the closures were in Texas, where the 147-school Fort Worth system closed for 10 days after confirmation of one case of swine flu at one campus and probable cases at three others. As of noon yesterday, schools in 10 other states reported closures to the U.S. Education Department.

The closure will be in effect for at least a week. The announcement comes one day after health officials announced the closure of Steele High School, where two students contracted the disease and a third case was pending.

All extracurricular activities also were cancelled.

"We don't have lab confirmation for any of the additional flu-like illnesses yet, but we've found enough illnesses associated with some of the other schools that we believe it's prudent to close all of them before classes resume on Monday," said Sandra Guerra, a DSHS regional director and the public health authority for Guadalupe County.