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Viruses cause most pediatric infections. Mixed viral or viral-bacterial infections of the respiratory and intestinal tracts are common, as is prolonged asymptomatic shedding of many viruses in childhood, especially in young children. Thus, the detection of a virus may be indicative of infection, but it may not always be the cause of a given illness or disease. Viruses are often a predisposing factor for bacterial respiratory infections (eg, otitis, sinusitis, and pneumonia). See Table 40–1 for an outline of viral illnesses described in this chapter.

Table 40–1.Outline of Chapter 40.

The epidemiology of respiratory viruses is frequently changing, as is demonstrated by the recent emergence of SARS-CoV-2, and the impact that social distancing measures had not only on COVID-19 disease but many other respiratory viruses as well, such as influenza, RSV, and others. As the world continues in its response to the COVID-19 pandemic and eventually settles into a “new normal” of disease burden and behavior, existing patterns of seasonality, transmission, diagnosis, and even treatment and prevention may change significantly.

Many respiratory viruses and herpesviruses can now be detected within 24 through antigen or nucleic acid detection techniques. Polymerase chain reaction (PCR) amplification of viral genes has led to detection of previously unrecognized infections. It is now possible to detect multiple organisms causing the same syndrome (eg, respiratory, gastrointestinal, encephalitis/meningitis) within a single test system (multiplex assay). The available tests vary in format and turnaround time and can include both viral and bacterial etiologies. New diagnostic tests have changed some basic concepts about viral diseases and made diagnosis of viral infections both more certain and more complex. Only laboratories with excellent quality-control procedures should be used. The availability of specific antiviral agents increases the value of early diagnosis for some serious viral infections. Table 40–2 lists diagnostic tests. The viral diagnostic laboratory should be contacted for details regarding specimen collection, handling, and shipping. Table 40–3 lists common causes of red rashes in children that should be considered in the differential diagnosis of certain viral illnesses.

Table 40–2.Diagnostic tests for viral infections.

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