Disease Burden Associated with ICD-9 Diagnosed Influenza and Related Complications in US Children Aged 6-35 Months

Background: Influenza disproportionately affects very young children, yet there is little recent literature on disease burden in this age group. This study estimated the incidence of diagnosed influenza and its related complications, along with the associated costs, in children aged 6-35 months.

Methods: A retrospective claims-based study (GSK study identifier: HO-15-15728) using MarketScan Commercial Database identified influenza cases (ICD-9 487 or 488) occurring between Oct 1 and May 31 during 2010-2014. Eligible children were continuously enrolled for 12 months in a given influenza season (N=68,836). Complications potentially linked to influenza were identified within 21 days after the influenza diagnosis using ICD-9 codes. Influenza cases were matched 1:2 to children without influenza. All-cause and influenza-specific healthcare use and costs were estimated during 21 days of follow-up. Generalized linear models estimated the incremental effect of influenza and complications on healthcare costs.

Results: The seasonal incidence of influenza was 26.8 per 1,000 children (95% CI: 26.6-27.0) with 24.9% experiencing ≥1 influenza-related complication (95% CI: 24.6-25.2). Comparing 68,774 influenza cases to 137,441 matched controls: cases were more likely to have an all-cause hospitalization (1.7% vs. 0.2%) or emergency room (ER) visit (14.0% vs. 2.4%) (all p<0.001). Influenza cases with a complication were more likely to have an influenza-related hospitalization (4.5% vs. 0.7%) or ER visit (19.1% vs. 11.2%) compared to those without a complication (all p<0.001). Adjusting for demographic and clinical characteristics, all-cause costs were higher for influenza cases vs. controls ($902 vs. $496) and influenza-related costs were higher for influenza patients with vs. without complications ($1,160 vs. $386) (all p<0.001).

Conclusion: Children aged 6-35 months with diagnosed influenza experienced higher disease burden than those without influenza; among influenza patients, those who experienced an influenza-related complication had significantly higher costs than those without complications. Better prevention of influenza through improved vaccination coverage could reduce healthcare expenditures in children aged 6-35 months.