WASHINGTON — Scores more schools shut down around the country because of the swine flu virus at week's end and Education Secretary Arne Duncan offered tips to teachers and students on how to deal with classroom interruptions.

Federal officials closely watched developments as at least two dozen new cases of swine flu were reported.

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 7 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 more than 430 schools had closed, affecting about 245,000 children in 18 states. That was about 100 more schools reported closed than reported on Thursday.

The latest developments in the flu scare — more intense in neighboring Mexico than in the United States — came as the Centers for Disease Control and Prevention reported the virus had been confirmed in more U.S. states.

Confirmed cases had risen from 109 on Thursday to 161 Friday, the CDC said, with the flu reported in about double the number of states as the 11 reported Thursday. The U.S. death toll remained at one — the Mexican toddler who visited Texas with his family and died there.