Hospitalization, Death From H1N1 Influenza Can Occur at Any Age

by Fran Lowry

H1N1 influenza is emerging as an equal-opportunity threat, seriously affecting people of all ages — not just younger people, as had been thought — according to the results of a surveillance study from California published in the November 4 issue of the Journal of the American Medical Association.

"Pandemic influenza A(H1N1) emerged rapidly in California in April 2009," write Janice K. Louie, MD, MPH, from the California Department of Public Health, Richmond, and colleagues. "Preliminary comparisons with seasonal influenza suggest that pandemic 2009 influenza A(H1N1) disproportionately affects younger ages and causes generally mild disease."

However, data on the clinical features and populations at risk for complications from H1N1 influenza infection are still emerging, the authors add.
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The highest hospitalization rates per 100,000 were in infants 1 month old (35.8) and 2 months old (21.1). These rates were lower in infants aged between 3 and 12 months, ranging from 4.2 to 12.6 per 100,000.

The median length of stay in hospital was 4 days.

Although infants were hospitalized at greater rates than adults, individuals aged 50 years or older had the highest rate of death once hospitalized, the authors report.

The overall fatality rate was 11%. In children younger than 18 years, the death rate was 7%, and in persons older than 50 years, it was 18% to 20%.
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