(AP) -- At least seven people were in U.S. hospitals with swine flu Tuesday as the number of cases nationwide rose to 64 and a federal health official warned that deaths were likely.
Most of the nation's confirmed cases were in New York, where the city health commissioner said "many hundreds" of schoolchildren were ill at a school where several students had confirmed cases of swine flu.
Richard Besser, acting director of the federal Centers for Disease Control and Prevention, noted that although ordinary human flu accounts for 36,000 deaths every year, he was concerned by this strain.
"I fully expect we will see deaths from this infection," Besser said at an Atlanta news conference.
He said he did not know about a newspaper report of two deaths in two southern California hospitals in which the victims appeared to have suffered from swine flu symptoms.
New York has the largest number of swine flu cases, with a heavy concentration at a Catholic school in Queens where students recently went on a spring break trip to Mexico.
There were indications that the outbreak may have spread beyond the school, with two people having to be hospitalized and officials closing a school for autistic children down the road. Those cases have not been confirmed.
"It is here and it is spreading," New York City Health Commissioner Thomas Frieden said. "We do not know whether it will continue to spread."
Mayor Michael Bloomberg said that 82 of 380 students at P.S. 177, a school for autistic children, have called in sick. A third school in Manhattan is being evaluated because students there are sick, Frieden said.
The CDC said the country has 64 confirmed cases across five states, with 45 in New York, one in Ohio, two in Kansas, six in Texas and 10 in California. At least four other cases have been reported by states.
At least five other people have been hospitalized in the U.S., including three in California and two in Texas, Besser said.
The increase is not surprising. For days, CDC officials have said they expected to see more confirmed cases - and more severe illnesses. Health officials across the country have stepped up efforts to look for cases, especially among people with flu-like illness who had traveled to Mexico.
CDC officials also had warned that updates in the number of confirmed cases would at time be disjointed, as different states announce new information before the CDC's national count is updated.
A handful of schools around the country have closed over swine flu fears and some people are wearing masks, but it's mostly business as usual in the U.S., even at border crossings into Mexico.
In addition to thousands of deaths, often the elderly and the very young, about 200,000 people are hospitalized in the U.S. each year because of flu complications.
©2009 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.
Explore further: Swine flu cases up to 7, probe expanding