One quarter of Americans sick enough to be hospitalized with swine flu last spring wound up needing intensive care and 7 percent of them died, the first such study of the early months of the global epidemic suggests.
That's a little higher than with ordinary seasonal flu, several experts said.
What is striking and unusual is that children and teens accounted for nearly half of the hospitalized cases, including many who were previously healthy. The study did not give a breakdown of deaths by age.
"Contrary to the perception among many people that this influenza, novel H1N1, is mild, these data vividly demonstrate that influenza can make you very, very ill," said William Schaffner, a Vanderbilt University flu expert and spokesman for the Infectious Diseases Society of America.
"Clearly, the best way to protect yourself and your family is to get vaccine as soon as it becomes available," said Schaffner, who had no role in the study but has consulted for swine flu vaccine makers.
The study was done by researchers at the U.S. Centers for Disease Control and Prevention, working with hospitals and state and local health departments. Results were published online Thursday by the New England Journal of Medicine.
Researchers led by the CDC's Seema Jain identified 272 patients hospitalized for at least a day from April through mid-June, when the 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.
Seven percent were pregnant, even though pregnant women make up only 1 percent of the general population.
Symptoms were different — 39 percent had diarrhea or vomiting versus only 5 percent with regular flu. About 40 percent had pneumonia. Seven percent died, and all had been put on breathing machines.