Multistate Surveillance for Laboratory-Confirmed, Influenza-Associated Hospitalizations in Children

BACKGROUND: Increasing use of rapid influenza diagnostics facilitates laboratory confirmation of influenza infections. We describe laboratory-confirmed, influenza-associated hospitalizations in a population representing almost 6% of children in the United States. METHODS: We conducted population-based surveillance for influenza-associated hospitalizations between October 1, 2003, and March 31, 2004, in 54 counties in 9 states (4.2 million children) participating in the Emerging Infections Program Network. Clinical characteristics, predictors of intensive care unit admission and geographic and age-specific incidence were evaluated. RESULTS: Surveillance identified 1,308 case-patients; 80% were or=6 months old had received at least one influenza vaccine dose that season. The overall incidence of influenza-associated hospitalizations was 36 per 100,000 children (range per state, 10 per 100,000 to 86 per 100,000). CONCLUSIONS: Influenza was an important cause of hospitalizations in children during 2003-2004. Hospitalizations were particularly common among children <6 months of age, a group for whom influenza vaccine is not licensed. Continued surveillance for laboratory-confirmed influenza could inform prevention strategies.