By ERICA WERNER, Associated Press Writer

WASHINGTON (AP) – President Barack Obama voiced hope Friday that the swine flu virus will run its course “like ordinary flus” as officials reported more than two dozen new cases and scores more schools shut down.

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 more than 400 schools had closed, affecting about 245,000 children in 18 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.

“I’m optimistic that we’re going to be able to manage this effectively,” Obama told reporters as he received an update from his Cabinet on the federal response to the health emergency. At the same time, he emphasized that the federal government is preparing as if the worst is still to come so that it won’t be caught flat-footed.

Obama’s fresh take on the flu scare – more intense in neighboring Mexico than in the United States but also present in some measure around the globe – came as the Centers for Disease Control and Prevention reported the virus has been confirmed in eight more U.S. states and seems to be spreading.

Confirmed cases have risen from 109 Thursday to 141 Friday, the CDC said, with the flu now reported in 19 states, up from 11. Separately, a few states reported slightly higher numbers, and the District of Columbia announced its first two probable cases. The U.S. death toll remained at one – the Mexican toddler who visited Texas with his family and died there.

The most recent onset of illness was Tuesday, CDC said, indicating a continuing spread, though no faster than the rate of the regular winter flu.

“We think the cases do continue to occur,” said CDC’s Dr. Anne Schuchat. But CDC also said the new swine flu virus lacks genes that made the 1918 pandemic strain so deadly.

Obama said it wasn’t clear whether the flu would be more severe than others before it, and he said the swine flu is a cause for special concern because it is a new strain and people have not developed an immunity to it.

Government agencies are preparing in case the flu comes back in a more virulent form during the traditional flu season, the president said, talking of an overarching effort to help schools and businesses while also responding to pleas for help from other countries.

While emphasizing at a press conference that the closures to date represent a tiny fraction of the almost 100,000 schools in the country, Education Secretary Arne Duncan instructed teachers, parents and students to be prepared if their school does close.

To teachers, Duncan said: “Think about reworking upcoming lesson plans so students can do their schoolwork at home if necessary.”

To parents: “Learn about what they’re learning at school. Keep them on task.”

And to students: “Don’t fall behind your peers at other schools that are still in session. Keep working hard.”

Many travelers have become increasingly concerned about going to Mexico, though authorities there said new cases were leveling off.

The Mexico City mayor said Friday that no new flu deaths were reported overnight for the first time since the emergency was declared a week ago. Mexico has confirmed more than 300 swine flu cases and has 16 confirmed deaths, although reports have indicated that roughly 120 may have died from it.

U.S. travelers have been advised to avoid nonessential travel to Mexico. Continental Airlines Inc., the biggest U.S. carrier to Mexico, said Friday it would halve the number of seats it sells to fly there. Delta Air Lines Inc. and UAL Corp.’s United Airlines also announced plans for reduced flights to Mexico, while smaller carriers were following suit.

Mormon church officials canceled church services in Mexico City until further notice and said they were delaying sending new missionaries to that country.

The energy secretary aide who apparently got sick helping arrange Obama’s recent trip to Mexico told The Associated Press when reached at his office Friday that he was feeling better.

The aide, Marc Griswold, a former Secret Service agent who was doing advance work for Energy Secretary Steven Chu, declined to elaborate beyond comments in The Washington Post.

“We’re not the Typhoid Mary family, for goodness sake,” he told the Post in a story published Friday. “We’ve been told that we’re not contagious. We’re already past the seven-day mark for that.”

The White House has said Griswold did not fly on Air Force One and never posed a risk to the president.

Though most U.S. cases have been relatively mild and have not required a doctor’s visit, U.S. precautions include shipping millions of doses of anti-flu drugs to states in case they’re needed, replenishing the U.S. strategic stockpile with millions more treatment courses, and shipping 400,000 treatment courses to Mexico.

The CDC added the following states to its list of those with confirmed cases: New Jersey with five cases, Delaware with four, Illinois with three, Colorado and Virginia with two, and Minnesota, Nebraska and Kentucky each with one.

CDC previously had confirmed cases in New York, Texas, California, South Carolina, Kansas, Massachusetts, Indiana, Ohio, Arizona, Michigan and Nevada.

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Associated Press writers Lauran Neergaard, Eileen Sullivan and Joan Lowy in Washington and Ben Nuckols in Baltimore contributed to this report.

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On the Net:

Health and Human Services Department swine flu site:

www.pandemicflu.gov