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Infants and preschool children experience 6 to 10 respiratory illnesses per year, and school-age children and adolescents experience 3 to 5 illnesses annually.1 Respiratory infections are predominantly viral infections that are classified into (1) upper respiratory tract infection (URI), meaning the common cold, rhinitis, pharyngitis, otitis media, and conjunctivitis, and (2) lower respiratory tract infection (LRI), namely croup, laryngitis, tracheobronchitis, bronchiolitis, and pneumonia. This section will focus primarily on LRIs occurring in children with viral infections including those associated with characteristic lower respiratory infection presentations, eg, respiratory syncytial virus as the primary cause of bronchiolitis, parainfluenza as the primary cause of croup, and influenza as a primary cause of febrile tracheobronchitis.

Upper respiratory infection is also often associated with viral infection. A large proportion of the otitis media associated with or following a viral respiratory infection is the result of a secondary bacterial infection in the middle ear (see Chapter 243). The likelihood varies dependent upon the particular virus responsible for the associated or antecedent viral respiratory infection. In one prospective study, the risk of developing acute middle ear infection or effusion ranged from 15% to 30% in children with culture-proven viral infections; respiratory syncytial virus infection carried the highest risk.2 However, in many instances, aspirate cultures from middle ears of children with otitis media yield only a respiratory virus. There is also evidence linking bacterial sinusitis to antecedent viral upper respiratory tract infection.

Understanding of the etiologic agents of respiratory infections has changed significantly in the last decade because of widespread application of molecular techniques. Numerous new respiratory viruses have been discovered, including human metapneumovirus, human bocavirus, and several new coronavirus strains. Moreover, the traditional epidemiology of some previously known viruses, such as rhinovirus, has been challenged as a result of polymerase chain reaction assays that exceed the sensitivity of viral culture. Nevertheless, the major associations established by traditional techniques of viral culture, antigen detection, and serology remain valid, eg, respiratory syncytial virus as the primary cause of bronchiolitis, parainfluenza as the primary cause of croup, and influenza as a primary cause of febrile tracheobronchitis.

Generally, specific viral diagnosis from nasopharyngeal aspirates or swabs can be achieved by viral isolation in culture, by rapid viral antigen-detection tests such as immunofluorescence and enzyme-linked immunosorbent assay, or by nucleic acid amplification tests such as polymerase chain reaction. Retrospective diagnosis may be achieved using serologic methods, but the delay inherent in waiting for a convalescent serum (3–4 weeks) makes this diagnostic method less useful in clinical decision making. The availability of specific antiviral therapies, including neuraminidase inhibitors oseltamivir and zanamivir for both influenza A and B infections, and ribavirin for select cases of respiratory syncytial virus infection, has increased the need for readily available, early, specific diagnosis.

Respiratory syncytial virus (RSV) is the foremost cause of viral lower respiratory tract disease in infants and toddlers. Severe disease is generally associated with primary infection, although ...

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