(CNN) -- U.S. health officials expressed concern Friday that a swine flu virus that has infected eight people in the United States matches samples of a virus that has killed at least 68 people in Mexico. Swine flu is usually diagnosed only in pigs or people in regular contact with them. U.S. health experts also are concerned because more than 1,000 people have fallen ill in Mexico City in a short period of time. "This situation has been developing quickly," said acting CDC director Richard Besser. "This is something we are worried about." New York health officials announced Friday they are testing about 75 students at a Queens school for swine flu after the students exhibited flu-like symptoms this week.
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NEW: Swine flu found in U.S. is same that killed at least 68 in Mexico
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NEW: The latest U.S. case of swine flu occurred in California, the CDC says
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Eight cases of the strain of swine flu have been confirmed in humans in the U.S.
All of the eight @placeholder patients have recovered, Besser said.