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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.
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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.
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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.
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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.
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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 ...