Detection of influenza A virus by radioimmunoassay and enzyme-immunoassay from nasopharyngeal specimens.

Four-layer (indirect) radioimmunoassay (RIA) and enzyme-immunoassay (EIA) techniques were developed for the detection of influenza A and B virus in the sonicated nasopharyngeal specimens from patients hospitalized for acute respiratory infection. Polystyrene beads (RIA) or polystyrene microtiter plates (EIA) were used as the solid-phase, guinea pig antivirus immunoglobulins as the catching antibodies, rabbit antivirus immunoglobulins as the secondary antibodies, and 125I-labeled sheep antirabbit (RIA) or horseradish peroxidase conjugated swine antirabbit (EIA) immunoglobulins as the detector antibodies. A comparison of the developed RIAs and EIAs with the immunofluorescence (IF) method was made with 41 influenza A IF-positive and 150 influenza A IF-negative specimens. Each of the 41 influenza A IF-positive specimens was positive by the influenza A RIA and negative by the influenza B RIA. Out of 150 influenza A IF-negative specimens 3 specimens were found with weakly positive results in influenza A and B RIAs, but in each of these 3 specimens the binding proved nonspecific by the corresponding confirmatory tests. Using the EIa technique and the same immunoreagents as in RIA, identical results were obtained in each selected specimen tested. The developed RIAs and EIAs proved to be as specific and sensitive as the IF technique, and they should be practical in the diagnosis of respiratory infections directly from nasopharyngeal specimens.