More than 40 U.S. children have died from the virus since it was first identified in this country in April. The report from the U.S. Centers for Disease Control and Prevention takes a comprehensive look at the first 36 deaths, and found some important differences in the pediatric death toll from swine flu as compared to seasonal flu:
-- Almost two-thirds of the children who died with swine flu had epilepsy, cerebral palsy or other neurodevelopmental conditions. In a previous flu season, only a third of pediatric deaths had those conditions.
-- Bacterial co-infections were a big danger, and were blamed in most of the deaths of otherwise healthy children. Co-infections usually occur when a patient, weakened by a virus, then gets hit by a bacterial bug.
The CDC released the report through one of its publications, Morbidity and Mortality Weekly Report.
Swine flu has caused more than 1 million illnesses in the United States, the CDC estimates. More than 550 deaths and 8,800 hospitalizations have been reported to date.
It's hard to say whether children have accounted for a higher proportion of deaths from swine flu than they normally do from seasonal flu, though CDC officials say that seems to be true. The CDC doesn't monitor seasonal flu deaths as closely as it does swine flu, and it has no comprehensive count of annual seasonal flu deaths to enable such a comparison.
The new report focuses on lab-confirmed swine flu deaths reported through Aug. 8. The CDC hasn't been able to do as complete an analysis of cases that have come in since then, said Dr. Cynthia Moore, a CDC medical officer who was one of the study's co-authors.
Through Aug. 8, there were 477 total swine flu deaths, including 36 in children.
Only about 20 percent of those children were age 4 or younger. That's unusual: Often 50 percent or more of seasonal flu deaths are in infants and toddlers, who have less mature immune systems and smaller air passages and are generally in more danger from respiratory infections.
"There's a lot of school-aged children" in the death count, said Dr. Beth Bell, a CDC epidemiologist who is a leader in the agency's swine flu response efforts.
It's not clear why such a large percentage of the swine flu pediatric deaths are in kids aged 5 and older. It simply may be because older children were more likely to encounter the virus -- at schools, summer camps -- than very young children who spend more time at home, Bell said.
The initial numbers in the report are small and the CDC will need to look at more reports to see if the trends hold up, CDC officials said.
Two-thirds of the children who died had high-risk medical conditions. Nearly all of them had an illness related to the nervous system, including mental retardation, cerebral palsy and epilepsy and other seizure disorders.
Years ago experts recognized that children with neurodevelopmental conditions are at higher risk of serious complications from the flu. But the proportion of swine flu victims with that kind of underlying condition was swine flu percentages are high compared to a previous flu season, CDC officials said.
It's not clear how significant that finding is, because many of the children had other medical problems that had weakened their bodies, CDC officials said.
Of the children who were healthy before they got swine flu, many were probably killed by a one-two punch of swine flu working with a bacterial co-infection, CDC officials said.
Bacterial co-infections have been an increasingly noticed danger since the government started tracking pediatric flu deaths in 2004. So their occurrence with swine flu was not a surprise, but emphasized the needs for parents and doctors to be alert to the danger and give the child antibiotics when appropriate, CDC officials said.