Health experts say that is a little higher than with ordinary seasonal flu. They say the biggest difference is that nearly half of those hospitalized with the new swine flu have been children and teens. Flu usually strikes hardest in the elderly.

The U.S. Centers for Disease Control and Prevention did the study, with local and state health departments. Results were published online Thursday by the New England Journal of Medicine.

Researchers identified 272 patients hospitalized for at least a day from April through mid-June, when the novel virus caused its first wave of cases. That's about one-fourth of the total hospitalizations for swine flu reported during that time, but researchers only studied lab-confirmed cases and patients who agreed to be part of the study.

Three-fourths of these patients had other health problems, such as diabetes—typical of seasonal flu, too. However, only 5 percent were 65 and older; ordinary seasonal flu usually hits hardest in the elderly.

Symptoms were different—39 percent had diarrhea or vomiting versus only 5 percent with regular flu. About 40 percent had pneumonia.
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