Immunofluorescence testing of exfoliated respiratory cells and enzyme immunoassay for viral antigens are sensitive, specific techniques for detecting some viruses but are not often routinely used. Except for viruses that are more difficult to isolate, such as RSV, these tests are generally less sensitive than cell culture. Commercially available immunoassays are efficient for detecting influenza A and RSV in pediatric samples. A antigen in upper respiratory secretions, depending on sample type, and can be completed within 20 minutes. However, in older adults, nasopharyngeal samples are an insensitive means of detecting RSV antigen, and serology is more sensitive than cell culture.
Serologic diagnosis requires paired serum specimens and is intrinsically slower than direct methods.
Serology is not routinely available for coronavirus and rhinovirus infections. The combined use of cultures, antigen detection, and serology provides the highest yield for important respiratory viral pathogens in hospitalized adults.