Swine flu fears close schools in NY, Texas, Calif.

(AP) -- Esti Lamonaca's illness started with a high fever, a cough and achy bones, just a couple of days after she returned from a spring break trip on the beach in Cancun with friends. By the weekend, her voice was hoarse and she was wearing a surgical mask.

The 18-year-old senior is one of at least eight students at her New York City high school who health officials say have been sickened by a strain of swine flu suspected in the deaths of 103 people in Mexico. It has now spread to the United States, where authorities have confirmed 20 cases.

However, all of those sickened in the U.S. have recovered or are recovering. That's a stark difference from the lethal outbreak in Mexico that authorities can't yet explain.

Officials at Lamonaca's school, St. Francis Preparatory in Queens, learned that something was wrong there on Thursday when students started lining up at the nurse's office complaining of fever, nausea, sore throats and achy bones. It wasn't long before the line was out the door.

The nurse notified the city Health Department that day. On Friday, more students were getting sick, and the department dispatched a team to the school at about 1:30 p.m. But they got caught in traffic and didn't arrive until 3:30 p.m, just as classes were letting out for the weekend, said Brother Leonard Conway, the school's principal.

By then, there were only a few students left, and health officials quickly tested them for swine flu. While only eight cases are confirmed, more than 100 students are suspected to have been infected. Officials think they started getting sick after some students returned from the spring break trip to Cancun.

The U.S. government declared a public health emergency Sunday to respond to the outbreak, which also has sickened people in Kansas, California, Texas and Ohio. Many of them had recently visited Mexico. Roughly 12 million doses of the antiviral drug Tamiflu will be moved from a federal stockpile to places where states can quickly get their share if they decide they need it, Homeland Security Secretary Janet Napolitano said.

Cleaning crews spent Sunday scrubbing down St. Francis, which will be closed for days.

"I haven't been out of my house since Wednesday and am just hoping to make a full recovery soon," Lamonaca said. "I am glad school is closed because it supposedly is very contagious, and I don't want this to spread like it has in Mexico."

Some schools in Texas and California also were closing after students were found or suspected to have the flu.

The outbreak has people on edge across the country.

Officials along the U.S.-Mexico border asked health care providers to take respiratory samples from patients who appear to have the flu. Travelers were being asked if they visited flu-stricken areas.

In San Diego, signs posted at border crossings, airports and other transportation hubs advised people to "cover your cough." At Los Angeles International Airport, Alba Velez, 43, and her husband Enrique, 46, were wearing blue face masks - purely as a precaution - when they returned from a trip to Mexico.

The Los Angeles couple hadn't seen anyone sick while in Guadalajara but were nervous because of the stream of information about new cases. The two were wearing the masks because they're "just cautious," Enrique Velez said.

It was a different story for travelers heading south of the border.

"I'm worried," said Sergio Ruiz, 42, who checked in for a flight to Mexico City after a business trip to Los Angeles and planned to stay inside when he got home. "I'm going to stay there and not do anything."

In Ohio, a 9-year-old boy was infected with the same strain suspected of killing dozens in Mexico, authorities said. The third-grader had visited several Mexican cities on a family vacation, said Clifton Barnes, spokesman for the Lorain County Emergency Management Agency.

"He went to a fair, he went to a farm, he went to visit family around Mexico," Barnes said.

The boy has a mild case and is recovering at home in northern Ohio, authorities said.

In New York, Jackie Casola - whose son Robert Arifo is a sophomore at St. Francis - said her son told her a number of students had been sent home sick Thursday and hardly anyone was in school Friday.

Arifo hasn't shown any symptoms, but some of his friends have, his mother said. And she has been extra vigilant about his health.

"I must have drove him crazy - I kept taking his temperature in the middle of the night," she said.

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Associated Press writers Josh Hoffner, Jennifer Peltz and Deepti Hajela in New York, Michael R. Blood in Los Angeles, Michelle Roberts in San Antonio and Meghan Barr in Columbus, Ohio, contributed to this report.

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