Influenza is a common disease of childhood and is responsible for significant illness, according to background information in the article. Healthy young children are hospitalized for influenza-related illness at rates similar to those for elderly persons and adults with chronic medical conditions. Perhaps most concerning to parents and physicians is the potential for serious influenza-associated complications, including carditis (inflammation of the heart), encephalitis, myositis (inflammation of muscle tissue), pneumonia, respiratory failure, and death.
Population-based studies suggest that individuals with certain chronic medical conditions are at increased risk of serious complications of influenza infection. The Advisory Committee on Immunization Practices (ACIP) has identified 9 groups of chronic medical conditions for which annual influenza vaccination is recommended. They include asthma, chronic lung disease, cardiac disease, immunosuppression, hemoglobinopathies (a blood disease characterized by the presence of abnormal hemoglobins in the blood), chronic renal dysfunction, metabolic and endocrine conditions, long-term salicylate (aspirin and some other drugs) therapy, and pregnancy. Despite the frequency of influenza infection and the prevalence of these chronic medical conditions, little is known about their relative contribution to the development of serious influenza-associated complications.
Ron Keren, M.D., M.P.H., of The Children's Hospital of Philadelphia, and colleagues conducted a study to identify chronic medical conditions that were associated with respiratory failure in children hospitalized with influenza. In addition to the current ACIP-designated high-risk conditions, the researchers also examined three other categories of chronic medical conditions--neurological and neuromuscular disease (NNMD, such as muscular dystrophy), gastroesophageal reflux disease (GERD), and history of prematurity, that in recent studies have been associated with influenza hospitalization and severe influenza-related complications. The study included patients aged 21 years or younger hospitalized at The Children's Hospital of Philadelphia, with community-acquired laboratory-confirmed influenza during 4 consecutive influenza seasons (June 2000 through May 2004).
Of 745 children hospitalized with influenza, 322 (43 percent) had one or more ACIP-designated high-risk chronic medical conditions. NNMD, GERD, and history of prematurity were present in 12 percent, 14 percent, and 3 percent, of children, respectively. Thirty-two children (4.3 percent) developed respiratory failure. In further analyses, conditions associated with respiratory failure included NNMD (6 times increased risk), chronic pulmonary disease other than asthma (4.8 times increased risk), and cardiac disease (4 times increased risk). The predicted probabilities of respiratory failure derived from the multivariate model were 12 percent, 9 percent, and 8 percent for children with NNMD, chronic pulmonary disease, and cardiac disease, respectively. Children hospitalized with influenza who had 2 of these 3 chronic conditions had a 31 percent to 39 percent predicted probability of respiratory failure.
"The significantly increased probability of respiratory failure in children with NNMD hospitalized with influenza supports the ACIP's recent decision to add NNMD that may compromise respiratory function to the list of chronic conditions that warrant annual influenza vaccination. Coordinated efforts are needed to educate parents, primary care pediatricians, and pediatric neurologists about the risks of serious influenza complications and the need for annual vaccination for children with NNMD. Future studies should determine the risk of hospitalization among children with NNMD, the number of additional children with NNMD who will require annual vaccination, as well as the effectiveness and cost-effectiveness of the influenza vaccine in preventing hospitalizations and serious complications in these children," the authors conclude.
(JAMA.2005; 294:2188-2194. Available pre-embargo to the media at www.jamamedia.org)
Editor's Note: This work was supported by a grant from the Centers for Disease Control and Prevention (CDC). Dr. Keren was supported by a grant from the National Institute of Child Health and Human Development, Bethesda, Md.