NEW ORLEANS - Longitudinal studies evaluating the impact of influenza on children found they exhibit fever, irritability and respiratory symptoms, shed large amounts of virus for prolonged periods and act as vectors for disease spread. In addition, their systemic and mucosal responses to influenza are age-dependent.
"If we look at the frequency in which children [younger than 1 year] presented with influenza to physicians in our clinic ... somewhere in the range of one in every 10 children would have a visit with influenza," said Peter Wright, MD, professor of pediatrics at Vanderbilt University in Nashville, Tenn., who spoke here at the 38th Annual Meeting of the Infectious Diseases Society of America.
"These are children without special risk. It's the same rate in 1- to 2-year-olds. Then that rate drops off significantly and it's one per 12 child years between the ages of 2 and 5 years old," he said.
Wright and colleagues looked at seven children who were hospitalized with influenza and estimated that there is one in approximately 300 children younger than 1 year hospitalized annually with influenza. For children ages 1 and 2 years, the rate is the same, but when children reach ages 2 to 5 years, it drops to fewer than one per 1,000.
Strains isolated from the seven hospitalized children were predominately influenza A(H3N2) (n=5).
"What's interesting is that these illnesses might not have normally been scored as having influenza as a component," said Wright, noting three of the children had significant bacterial complications, two presented with bacterial meningitis and one with periorbital cellulitis. Not mutually exclusive, two patients had croup, one had pneumonia, and one was a young child who was admitted to rule out sepsis.
According to Wright, the frequency with which different strains are isolated in children is of special interest. During a 25-year study at Vanderbilt University, H3N2 has been the predominant virus, with 192 isolates compared with 69 influenza B and 28 influenza A(H1N1) strains.
"This is not to say H1N1 doesn't have a reasonably high penetration into the pediatric population. Surveys on pre- and postepidemic sera demonstrated roughly 30% of children in a given year may have experienced H1N1; but it's not associated with more serious illness," said Wright.
In the 20 out of 25 years the Vanderbilt researchers saw influenza in the study population, H3N2 predominated in 14 of those years, influenza B predominated seven years and H1N1 predominated for two.
Signs and symptoms can differ by influenza strain, according to Wright. He noted that case patients' symptoms were more frequent with H3N2 than with influenza B or H1N1; and they included coryza, cough, vomiting and anorexia and a degree of febrile illness. "So 22% with H3N2 strains had temperatures >103° F as opposed to 13% with influenza B and 7% with H1N1," said Wright.
There are also differences in severity within the influenza strains; not with year-to-year variations as much as the differences are inherent in the strains themselves.
Influenza in children is also characterized by fever, with a substantial number of children having fevers >103° F (39.5° C).
Wright, citing a study that appeared this year in the New England Journal of Medicine noted there are approximately 70 excess hospitalizations per 10,000 children younger than 1 year, with rates dropping off substantially after the age of 1 but still elevated until the ages of 3 to 5 years.
"Influenza is perhaps responsible for about 15% to 30% of excess winter hospitalizations for respiratory illnesses," said Wright. "When you look at the estimated hospitalizations, the critical thing is that for low-risk and high-risk individuals, the rate in children younger than 1 year is comparable to adults older than 65. This is clearly a targeted group for prevention."
For more information:
- Wright P. Influenza in children and children in influenza. Session 9. Presented at the 38th Annual Meeting of the Infectious Diseases Society of America. Sept. 7-10, 2000. New Orleans.
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