Objective: To describe the characteristics and clinical courses of asthmatic children hospitalized with seasonal or 2009 pandemic H1N1 influenza and compare complications by influenza type.

Methods: During the 2003-2009 influenza seasons and the 2009 pandemic, we conducted surveillance of 5.3 million children aged 17 years or younger for hospitalization with laboratory-confirmed influenza and identified those with asthma (defined as those aged 2-17 years with a history of asthma in their medical record or a discharge code for acute asthma exacerbation or status asthmaticus). We collected data from medical records on medical history and clinical course; data on asthma severity and control were not routinely collected.

Results: During the 2003-2009 influenza seasons, 701 (32%) of 2165 children hospitalized with influenza had asthma; during the 2009 pandemic, 733 (44%) of 1660 children had asthma. The median age of the asthmatic children was 7 years, and 73% had no additional medical conditions. Compared with asthmatic children with seasonal influenza, a higher proportion with 2009 pandemic H1N1 influenza required intensive care (16% vs 22%; P=.01) and were diagnosed with pneumonia (40% vs 46%; P=.04), whereas equal proportions had respiratory failure (5% vs 5%; P=.8) and died (1% vs 1%; P=.4). More asthmatic children with influenza A (seasonal or pandemic) had diagnoses of asthma exacerbations compared with those with influenza B (51% vs 29%; P<.01).

Conclusions: The majority of asthmatic children hospitalized with influenza have no additional medical conditions. Complications such as pneumonia and need for intensive care occur in a substantial proportion, highlighting the importance of influenza prevention through vaccination among asthmatic children.