Other experts also weren't surprised by the finding.
"The burden of disease is still in younger people, but don't forget that older people can still get sick and, when they do, it's likely to be more severe," said Dr. Scott Lillibridge, assistant dean at Texas A&M Health Science Center School of Rural Public Health in Houston and executive director of the National Center for Emergency Medical Preparedness and Response.
"Clearly there are fewer elderly people getting this disease but it shouldn't surprise anybody that if an elderly person gets it and lands in the hospital they would have a higher death rate because it's a much frailer group. Twenty percent mortality in elderly people vs. 11 percent in young people -- I don't think that's shocking," said Dr. Jeffrey Boscamp, physician-in-chief at the Sanzari Children's Hospital at Hackensack University Medical Center in New Jersey.
A high proportion (about a third) of the California patients needed intensive care, the researchers found, and one-third of affected children needed ventilators.
The patterns seen here (and elsewhere) are markedly different from trends seen with the seasonal flu, where hospitalizations and deaths are disproportionately seen in older people, the authors stated.
More than one-third of adults with H1N1 in this group had gastrointestinal symptoms such as nausea, vomiting or diarrhea, vs. only about 5 percent with the seasonal flu, the team said
In related news, a research letter in the same issue of JAMA reports a case of rhabdomyolysis -- a breakdown in muscle tissue -- in a 28-year-old woman who contracted H1N1 in June of this year. Doctors at Stanford University Medical Center say that -- like many at-risk patients -- this woman was obese. She also had a family history of sickle cell anemia and had smoked two or three cigarettes a day for the past year.
Rhabdomyolysis has been associated with different strains of flu and now, the authors stated, doctors should be on the lookout for this possible complication in patients with H1N1 as well. The patient in question became very sick and required intensive care but has since recovered.
There's more on H1N1 flu at the U.S. Centers for Disease Control and Prevention.
SOURCES: Janice K. Louie, M.D., public health medical officer, California Department of Public Health; Edward Walsh, M.D., professor, medicine, University of Rochester Medical Center, and chief, infectious diseases, Rochester General Hospital, New York; Scott Lillibridge, M.D., assistant dean, Texas A&M Health Science Center School of Rural Public Health, Houston; Jeffrey Boscamp, M.D., physician-in-chief, Sanzari Children's Hospital, Hackensack University Medical Center, New Jersey; Nov. 3, 2009, teleconference with: Thomas Frieden, M.D., director, U.S. Centers for Disease Control and Prevention, Atlanta; Nov. 4, 2009, Journal of the American Medical Association