TUESDAY, Nov. 3 (HealthDay News) -- The age of people hospitalized with H1N1 influenza infection in California during the summer of 2009 was typically younger than the age commonly seen with seasonal influenza, and infants had the highest rates of hospitalization and those aged 50 and older had the highest mortality, according to research published in the Nov. 4 issue of the Journal of the American Medical Association.

Janice K. Louie, M.D., of the California Department of Public Health in Richmond, and colleagues analyzed data from 1,088 cases of hospitalization or death from H1N1 reported in California from April 23 to Aug. 11.

The researchers found that the median age for cases was 27 years, while infants younger than 1 year had the highest rate of hospitalization. Sixty-eight percent of cases had other conditions previously associated with severe influenza, such as chronic lung disease or immunosuppression. The overall fatality rate was 11 percent, with 118 cases dying; mortality was highest in persons aged 50 years or older.

"Clinicians should not be falsely reassured by previous good health, young age, and absence of major comorbidities because these characteristics do not exclude the potential for respiratory failure and death. Likewise, major comorbidities, tobacco use, pregnancy, and possibly obesity may increase the risk. On the other hand, a majority of patients can survive intensive care for this illness, even if antiviral treatment was not initiated within 48 hours of clinical onset," writes the author of an accompanying editorial.

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