Direct immunofluorescent studies of infection with respiratory syncytial virus

Detection of respiratory syncytial virus in clinical specimens by viral culture, direct and indirect immunofluorescence, and enzyme immunoassay

We evaluated prospectively the detection of respiratory syncytial virus (RSV) by culture and by direct antigen detection using an indirect immunofluorescence assay (IFA), a direct monoclonal immunofluorescence assay (DFA), and a monoclonal enzyme immunoassay (EIA). Of 221 specimens, 95 (43%) were culture positive for RSV, 4 (1.8%) contained more than one virus, and 17 (7.6%) contained a virus other than RSV. Overall, HEp-2 and Flow 6000 cells grew significantly more RSV isolates (82 and 72%, respectively) than A549 cells, which grew only 29% of the isolates. The mean time for RSV detection with HEp-2 cells was 2.9 days. This was significantly less than the mean time for RSV detection with either Flow 6000 cells (6.1 days) or A549 cells (6.4 days). Of 221 specimens, 129 were tested simultaneously by culture, IFA, and DFA. Of these 129 specimens, 62 (48%) were positive by culture, 69 (53%) were positive by IFA, and 70 (54%) were positive by DFA. For 92 specimens screened simultaneously by culture, IFA, and EIA, positive results were obtained for 33 (36%) of the specimens by both culture and IFA and for 29 (32%) of the specimens by EIA. Of 126 culture-negative specimens, 21 (17%) were positive for RSV when determined by IFA. Conversely, 14 (15%) of 95 RSV culture-positive specimens were negative by IFA, whereas DFA missed 19% of the culture-positive specimens. Compared with culture, the Kallestad EIA kit had a sensitivity and specificity of 73 and 92% respectively, but missed 9 (27%) of 33 culture-positive specimens. These data demonstrate that isolation by culture continues to be important for viral diagnosis of REV infections and that for valid comparative studies between viral isolations and rapid detection methods, both sensitive host cells and appropriate test conditions are required.

Peroxidase-antiperoxidase assay for rapid detection of respiratory syncytial virus in nasal epithelial specimens from infants and children

A peroxidase-antiperoxidase (PAP) assay for the rapid detection of respiratory syncytial virus was compared with the indirect immunofluorescence method and with viral culture. Nasal epithelial specimens from 147 infants and children with acute respiratory infections were obtained and evaluated for the presence of respiratory syncytial virus antigens. Sensitivity, specificity, and accuracy by PAP were 91.7, 84.8, and 87.1%, respectively, and 87.0, 88.5, and 88.0%, respectively, by immunofluorescence compared with viral culture. The PAP assay was found to be as accurate as the indirect immunofluorescence method and more convenient to perform, since the color reaction and cell morphology were more easily observable by light microscopy. A new specimen collection method is reported; gentle scraping of the superficial nasal mucosa by the Rhino-probe method provided sufficient numbers of epithelial cells to perform multiple assays.