Incidence of Medically Attended Respiratory Syncytial Virus and Influenza Illnesses in Children 6–59 Months Old During Four Seasons

Simpson, Melissa D.; Kieke, Burney A.; Sundaram, Maria E.; McClure, David L.; Meece, Jennifer K.; Sifakis, Frangiscos; Gasser, Robert A.; Belongia, Edward A.

Acute respiratory illnesses (ARIs) are among the leading causes of pediatric morbidity and mortality in developing and wealthy regions of the world [1, 2] . Viruses account for most ARIs in children younger than 5 years, and they are the leading cause of community-acquired pneumonia in this age group [3] . Children experience approximately 3-6 ARIs per year, and the spectrum of illness ranges from mild to life-threatening [4] . Respiratory syncytial virus (RSV) and influenza are 2 pathogens that cause serious illness and account for a substantial proportion of viral respiratory infections in children. Respiratory syncytial virus is a major cause of bronchiolitis in infants, and approximately 22% of lower respiratory infections have been attributed to RSV [5] . A population-based study of children younger than 5 years found that 8% of all primary care visits and 18% of all emergency department visits for ARI were attributed to RSV [6] . Influenza is a major cause of hospitalization among children under 24 months of age [7] , and approximately 10%-25% of outpatient ARI visits are related to influenza during seasonal epidemics [8] .