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Diagnosis of RSV infection is made by detection of the virus or viral antigens in respiratory secretions, typically using viral culture, rapid antigen detection tests, or reverse transcription-polymerase chain reaction (RT-PCR).
The gold standard is viral culture, but this takes time. Rapid antigen detection tests have relatively low sensitivity compared to culture or PCR but very high specificity. RT-PCR is the most sensitive method but can remain positive for weeks after the live virus is gone.
The preferred diagnostic specimens are nasopharyngeal aspirates or washes, but nasopharyngeal swabs are frequently used due to easier collection.
Chest X-rays are nonspecific, often showing hyperinflation and peribronchial thickening. Complete blood counts often show lymphopenia and eosinopenia.
Testing for other viruses like influenza is important, as coinfections may occur. RSV diagnosis should be confirmed before initiating any specific antiviral treatment.