A swine flu outbreak at a New York school may have infected over 100 people after a group of pupils returned from a spring holiday in Cancun, Mexico.

Officials said today that there were 28 confirmed cases and 17 suspected cases of the swine flu at the St Francis Prep School, and that more than 100 pupils had complained of flu-like symptoms.

"We suspect there were probably more than 100 cases of swine flu at St Francis," said Thomas Frieden, the city health commissioner.

Michael Bloomberg, the city's Mayor, said the outbreak at church school was the only cluster of cases so far identified in New York.

The outbreak has not spread beyond the school's pupils and family members, officials said. Testing at a Bronx day-care centre where several people had fallen ill turned up negative.

The cases at St Francis were mild and, unlike in Mexico, did not appear to be life-threatening.

"There is nothing to date to suggest that this flu in New York City is any more risky than normal flu," Mr Bloomberg said.

The outbreak at St Francis, the largest Catholic secondary school in the United States, began when a dozen pupils returned from a holiday in Cancun. Ill pupils began queueing up to see the school nurse on Thursday complaining of fever, nausea, sore throats and achy bones. The nurse alerted health authorities.

The school is closed for two days while clean-up crews scrub the classrooms and hallways to clear the virus.

Mayor Bloomberg said it was "speculation" that the virus had travelled to New York from Mexico.

New Yorkers refused to panic and went about their business normally, but about 550 people called a city hot-line for help.

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