Swine Flu Found No More Severe Than Seasonal Virus

Children infected in last year’s swine flu pandemic were no more likely to be hospitalized with complications or get pneumonia than those who catch seasonal strains, according to a study that challenges previous reports.

About 1.5 percent of children with the H1N1 swine flu strain were hospitalized within 30 days, compared with 3.7 percent of those sick with a seasonal strain of H1N1 and 3.1 percent with an H3N2 virus, researchers said today in the Journal of the American Medical Association. The report compared outcomes in Wisconsin of 545 patients with swine flu versus 853 patients with seasonal strains beginning in 2007.

Approximately 50 million people in the U.S. caught swine flu last year. Children were more likely to get sick than in a typical year, leading previous studies to conclude that the virus not only spread more easily but also was more severe. Today’s study was more in line with CDC estimates that about half as many people died of flu last year as in a typical year.

“The risk of most serious complications was not elevated in adults or children,” the study’s authors wrote. “Children were disproportionately affected by 2009 H1N1 infection, but the perceived severity of symptoms and risk of serious outcomes were not increased.”

Influenza is a rapidly evolving virus, and the severity of the season depends on which strains are circulating and how well a population has been inoculated. About 12,000 people of all ages died in the swine flu outbreak, according to the CDC. Annual deaths associated with seasonal flu ranged from 3,349 to 48,614 during the last 30 years.

Report Limitations

While today’s report was limited by its size and geographic reach, the study was large enough to show that swine flu wasn’t much more severe for kids, according to the researchers.

Comparing outcomes from different flu seasons is difficult, as survey methods vary. The Wisconsin study was set up to examine the same group of people during three flu seasons to reach a more precise comparison. Illness was assessed through interviews and flu tests. Patients’ medical records were reviewed to determine the severity of the illness and outcomes.

To contact the reporter on this story: Tom Randall in New York at trandall6@bloomberg.net.

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