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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 is not always proof that it is the cause of a given illness. Viruses are often a predisposing factor for bacterial respiratory infections (eg, otitis, sinusitis, and pneumonia).

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 40–1 lists diagnostic tests. The viral diagnostic laboratory should be contacted for details regarding specimen collection, handling, and shipping. Table 40–2 lists common causes of red rashes in children that should be considered in the differential diagnosis of certain viral illnesses.

Table 40–1.Diagnostic tests for viral infections.

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