Objectives: Few studies have examined the characteristics and clinical course of children hospitalized with laboratory-confirmed influenza. We sought to (1) estimate the age-specific incidence of influenza-related hospitalizations, (2) describe the characteristics and clinical course of children hospitalized with influenza, and (3) identify risk factors for prolonged hospitalization.

Patients and methods: Children < or = 21 years of age hospitalized with community-acquired laboratory-confirmed influenza at a large urban children's hospital were identified through review of laboratory records and administrative data sources. A neighborhood cohort embedded within our study population was used to estimate the incidence of community-acquired laboratory-confirmed influenza hospitalizations among children < 18 years old. Risk factors for prolonged hospitalization (> 6 days) were determined by using logistic regression.

Results: We identified 745 children hospitalized with community-acquired laboratory-confirmed influenza during the 4-year study period. In this urban cohort, the incidence of community-acquired laboratory-confirmed influenza hospitalization was 7 per 10,000 child-years of observation. The median age was 1.8 years; 25% were infants < 6 months old, and 77% were children < 5 years old. Many children (49%) had a medical condition associated with an increased risk of influenza-related complications. The incidence of influenza-related complications was higher among children with a preexisting high-risk condition than for previously healthy children (29% vs 21%). However, only cardiac and neurologic/neuromuscular diseases were found to be independent risk factors for prolonged hospitalization.

Conclusions: Influenza is a common cause of hospitalization among both healthy and chronically ill children. Children with cardiac or neurologic/neuromuscular disease are at increased risk of prolonged hospitalization; therefore, children with these conditions and their contacts should be a high priority to receive vaccine. The impact on pediatric hospitalization of the new recommendation to vaccinate all children 6 months to < 5 years old should be assessed.