A US study of flu cases in adults and children living in Wisconsin concluded that the risk of serious complications from 2009 H1N1 swine flu was no higher than the risk of serious complications from recent seasonal flu strains, according to JAMA.
Researchers from the Marshfield Clinic Research Foundation, Marshfield, Wisconsin, and the Influenza Division at the Centers for Disease Control and Prevention (CDC) in Atlanta, Georgia, also found that patients who contracted the 2009 swine flu tended to be younger than those who contracted seasonal flu.
6.874 screened patients were tested for influenza A during the 2007-08 and the 2008-09 flu seasons, and also from May to November 2009. Among this population, they identified 545 patients of median age 10 years had been infected with 2009 H1N1 swine flu, 221 of median age 11 years with seasonal H1N1, and 632 patients of median age 25 years with H3N2, another serotype influenza A virus. When they compared these case numbers to outcomes in the patients' medical records, researchers found that: During the 30 days of follow up, compared with seasonal H1N1 and H3N2, the 2009 H1N1 swine flu was not linked to higher rates of hospital admission or pneumonia among children.
In adults, a similar picture emerged, with no significantly higher rates of hospital admissions or pneumonia for 2009 H1N1 swine flu than for seasonal flu. Also, during the 30 days of surveillance follow up, there were no significant differences by strain among the proportion of children or adults with serious outcomes (ie hospital admissions or pneumonia).
"Our results suggest that the clinical manifestations and risk of hospital admission are similar for 2009 H1N1 and other seasonal influenza A strains among those presenting for medical care and documented to have influenza infection."
Overall, they found that while more children appeared to contract 2009 H1N1 swine flu, the perceived severity of complications, as measured by counting hospital admissions and cases of pneumonia, were no worse in swine flu cases than in seasonal flu cases of the A viruses.