PURPOSE OF THE STUDY.
To estimate the rates of hospitalization with seasonal influenza in children younger than 18 years from a large, diverse surveillance area during 2003–2008.
A case-subject was defined as a child younger than 18 years residing in the surveillance area who was hospitalized with laboratory-confirmed influenza virus infection from the 2003–2004 and 2007–2008 influenza seasons. Surveillance was conducted through the Centers for Disease Control and Prevention Emerging Infections Program Network, which included up to 10 different states and 5.3 million children.
Hospitalized children were identified retrospectively; clinicians made influenza-testing decisions. Data collected from the hospital record included demographics, medical history, and clinical course. Incidence rates were calculated with census data.
The highest hospitalization rates occurred in children younger than 6 months (seasonal range: 9–30 per 10 000 children), and the lowest rates occurred in children aged 5 to 17 years (0.3–0.8 per 10 000). Overall, 4015 children were hospitalized, 58% of whom were identified with rapid diagnostic tests alone. Forty percent of the children who were hospitalized had underlying medical conditions; asthma (18%), prematurity (15% of children younger than 2 years), and developmental delay (7%) were the most common. Severe outcomes included ICU admission (12%), respiratory failure (5%), bacterial coinfection (2%), and death (0.5%).
Influenza-associated hospitalization rates varied according to season and age and likely underestimated true rates, because many hospitalized children are not tested for influenza. The proportion of children with severe outcomes was substantial across seasons. Quantifying the incidence of influenza hospitalization and severe outcomes is critical to defining disease burden.
Children younger than 6 months had the highest rates of hospitalization across all seasons. Because these children cannot receive the influenza vaccine, immunization of household contacts, out-of-home caregivers of children in this age group, and pregnant women and women who are or will become pregnant during influenza season remains the primary way to reduce the risk of influenza in infants younger than 6 months. The data from this investigation should provide an even stronger argument for recommending the influenza vaccine for appropriate patients.
- Copyright © 2011 by the American Academy of Pediatrics