Surveillance for influenza admissions among children hospitalized in Canadian immunization monitoring program active centers, 2003-2004

OBJECTIVES. Influenza is a common childhood infection that may result in hospitalization. Our objectives were to (1) determine characteristics of children hospitalized for influenza and disease manifestations and (2) obtain baseline data before implementation of new recommendations for routine immunization of young children and their caretakers against influenza. METHODS. All of the children hospitalized with laboratory-confirmed influenza at 9 Canadian tertiary care hospitals during the 2003-2004 influenza season were identified from virology laboratory reports, and their charts were reviewed. RESULTS. There were 505 children admitted because of influenza. Fifty-seven percent were < 2 years old. Previously healthy children accounted for 58% of all of the cases. Pulmonary and neurologic disorders were the most common underlying chronic conditions. Fever and cough were the most frequent manifestations. Seizures occurred in 9% of cases. Serious complications included myocarditis (2), encephalopathy (6), and meningitis (1). There were 3 influenza-related deaths. Mean duration of hospitalization was 5.3 days. Twelve percent of children required ICU admission, and 6% required mechanical ventilation. Antibiotic therapy was administered in 77% of cases, and 7% received anti-influenza drugs. Information on influenza vaccination was available for 84 of 154 children identified as vaccine candidates. Twenty two had received vaccine, but only 7 children had been fully immunized > 14 days before the onset of illness. CONCLUSIONS. Healthy young children and children with chronic conditions are at risk for serious illness with influenza. Ongoing surveillance is needed to evaluate the impact of changing immunization recommendations on the burden of influenza illness in children.