NEW YORK, April 26 (Xinhua) -- New York Mayor Michael Bloomberg said Sunday that the Centers for Disease Control and Prevention (CDC) confirmed that eight high school students from city have been infected with swine flu.

    Bloomberg told a press conference the cases are mild and that many are recovering.

Father Bill Sweetney, principal of St. Francis Preparatory School, addresses the media outside the school in New York City borough of Queens April 26, 2009. New York Mayor Michael Bloomberg said Sunday that the Centers for Disease Control and Prevention ( CDC) confirmed that eight students of St. Francis Preparatory School have been infected with swine flu. (Xinhua/Liu Xin) Photo Gallery>>>

    About 100 students at St. Francis Preparatory School in Fresh Meadows, Queens, became sick with flu symptoms in the last few days. Some students' family members also fell ill.

    Bloomberg said some of the school's students had a spring break in Mexico.

    "It is most likely to be brought back from Mexico, but nobody knows."

Journalists make coverage outside the St. Francis Preparatory School in New York City borough of Queens April 26, 2009. New York Mayor Michael Bloomberg said Sunday that the Centers for Disease Control and Prevention ( CDC) confirmed that eight students of St. Francis Preparatory School have been infected with swine flu. (Xinhua/Liu Xin) Photo Gallery>>>

    St. Francis, the largest private Catholic high school in the United States, has 2,700 students. The school has announced on its website that it will be closed on Monday and Tuesday.

    Other schools in the city will remain open as usual on Monday, Bloomberg said.

    New York State authorities have stepped up preparedness against the outbreak, and governor David Paterson said Saturday that 1,500treatment courses of the antiviral drug Tamiflu had been sent to New York City.

    In Washington, CDC acting director Richard Besser said across the country, a total of 20 swine flu cases have been confirmed.

    The other confirmed cases are seven in California, two in Texas, two in Kansas and one in Ohio, Besser told a White House press briefing.

    More cases and more severe illness among Americans are expected, Besser said.

Father Leonard Conway, principal of St. Francis Preparatory School, walks in the school building pasted with a notification reading "SCHOOL CLOSED MONDAY AND TUESDAY," in New York City borough of Queens April 26, 2009. (Xinhua/Liu Xin) Photo Gallery>>>

    The Barack Obama administration has declared a public health emergency, vowing to take active and aggressive measures to cope with the outbreak.

    No swine-flu-related deaths have been reported in the United States, but the outbreak has been much worse in neighboring Mexico, where more than 1,300 people are believed to have been infected, and 81 related deaths reported.

    The World Health Organization declared the outbreak a "public health emergency of international concern," but said it was too early to predict whether a pandemic would occur.