Time-resolved fluoroimmunoassay compared with virus isolation for rapid detection of respiratory syncytial virus in nasopharyngeal aspirates.

Two monoclonal antibodies against two distinct conserved epitopes of the respiratory syncytial virus (RSV) nucleocapsid protein were used in a direct time-resolved fluoroimmunoassay (TR-FIA) for the detection of RSV antigens in nasopharyngeal aspirates. The capture antibody was adsorbed to the solid phase of microdilution strip wells, and the indicator antibody was labeled with a europium chelate. Specimens and label were incubated simultaneously for 1 h at 37 degrees C in the coated wells. After the test samples were washed, fluorescence enhancement solution was added, strips were shaken, and the time-resolved fluorescence was measured. The test procedure took only 75 min, and the total time for 20 specimens, with pretreatment by sonication, was 2 to 3 h. We prospectively evaluated the detection of RSV in nasopharyngeal aspirates of pediatric patients by TR-FIA and by virus isolation in human diploid fibroblasts. TR-FIA detected 40 of 42 isolation-positive specimens. Nine additional isolation-negative specimens were positive by TR-FIA; all proved to be true positives by a blocking-type confirmatory assay. The sensitivity, specificity, positive predictive value, and negative predictive value for TR-FIA were 95, 96, 82, and 99%, respectively, of the values obtained by virus isolation and 96, 100, 100, and 99%, respectively, of the values obtained by virus isolation and the confirmatory assay.