A study of influenza and influenza-related complications among children in a large US health insurance plan database.

Background: Influenza places a substantial burden on the affected individual and society. While there are data available on the overall occurrence of influenza in children, less information is available on the differential impact of influenza on healthcare for previously healthy children and those at high risk of developing influenza-related complications.

Objective: To compare the frequency of influenza-related complications in healthy and 'at-risk' children, and quantify the associated use of medical resources and costs.

Design: Data were obtained from a large US-based health insurance plan database.

Main Outcome Measures And Results: A total of 23 188 health insurance claims with an influenza diagnosis were identified over the 3-year period 1995-1997 (3 247 834 patient-years). Influenza-related complications were observed in approximately a quarter of the total diagnosed cases, with younger children (0-4 years of age) at substantially greater risk. 'At-risk' children were more likely to develop influenza-related complications than otherwise healthy children. The greatest difference in incidence rate in the 0-4 year age group was for asthma (incidence rate ratio 8.7, 95% CI 5.2-14.4), and in the 5-14 year age group for asthma (incidence rate ratio 8.5, 95% CI 5.2-13.7) and acute sinusitis (incidence rate ratio 2.7, 95% CI 1.2-5.4). The average direct medical costs of influenza in children under 15 years with complications were more than 3.5 times higher than those without.

Conclusions: Measures to prevent and treat influenza-related complications are certainly warranted for at-risk children, although the elevated incidence rates for several common complications even among healthy children should prompt consideration of these measures for all children.