New York - New York state officials Wednesday downplayed the fact that New York has the highest total of confirmed cases of swine flu among ten US states, saying the situation was inexplicable - even as health workers were investigating 75 more probable cases and some schools remained closed.

New York Governor David Paterson and his health commissioner, Richard Daines, who noted there was no vaccine for swine flu, said they did not consider the swine flu outbreak any more important than unseasonal flu in springtime.

His remarks came just as the World Health Organization in Geneva raised the alert level to phase 5, which means swine flu is widespread and a pandemic is imminent.

In Mexico, 159 people are dead from influenza-type illness, and more than 1,000 people are hospitalized. Forty-nine cases have been confirmed as swine flu. The US reported the first death outside of Mexico on Tuesday, a Mexican toddler who was visiting in Texas.

New York state has 51 of the 91 cases confirmed in the US across ten states.

"The irony of this is that the flu does not seem to affect Americans the same way it affects Mexicans," Paterson said during a daily progress report on the swine flu situation in New York.

"This is a fear that there is nothing to substantiate with," Paterson said. "This is a fear that this is an illness for which there is no treatment, there is no data to accommodate it. For public safety we have to take the worst case scenario."

Paterson and New York Mayor Michael Bloomberg have repeatedly sought this week to reassure New Yorkers that all its swine flu cases were mild and everyone was recovering from it after the first medical treatment.

"The novelty is there seems to be a mixture of swine, bird and human influenza elements and therefore it could be a hybrid or a strain of influenza for which we are not familiar with," he said. "When it happens, we now have difficulty to find antibodies to a disease."

New York City's health commissioner Thomas Frieden echoed Paterson and others in saying that the swine flu has had little impact on the New York population. Frieden said about 1,000 New Yorkers died of flu each year while hundreds of thousands of others suffered in the flu season.

Frieden said health authorities had not discovered new swine flu cases since Tuesday and had checked many leads, which turned out to be false.

"If the (swine flu) virus becomes more serious and causes more deaths, then we will take more concerted action," Frieden said.

New York City reported school attendance at near normal range, at 88 per cent for all schools, with a total of 1.1 million students. Most of New York's cases were located in New York City and at a single high school, Saint Francis Preparatory School in Queens, where students who became ill had travelled to Mexico last month for spring recess.

Local news reports said Saint Francis school in Queens and the nearby Public School 177 were closed on Wednesday while tests were being conducted on students who showed severe flu symptoms. (dpa)