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Comparison of Immunofluorescence and Isolation Techniques in the Diagnosis of Respiratory Viral Infections of Children

The immunoflourescent antibody technique (IFAT) and cell culture isolation procedures were compared for their efficiency in the etiological diagnosis of viral respiratory illness in children. Before the IFAT was incorporated as a routine procedure, antisera used in the test were carefully calibrated to insure specificity. A study was then conducted in which 375 nasopharyngeal suctions were investigated by both IFAT and isolation for the presence of parainfluenza virus types 1, 2, and 3, respiratory syncytial, influenza A, and influenza B viruses. Methods already established in our hospital for patient management and specimen collection were not altered for the purposes of the study. The IFAT, as conventionally practiced in the detection of respiratory virus antigens, requires adequate numbers of ciliated epithelial cells. There were 68.5% specimens which contained cells suitable for IFAT, whereas 31.5% had either an insufficient number or inappropriate types of cells and could be used only for virus isolation. Cell-associated immunoglobulins were detected in 16% of those specimens with adequate cells. When all specimens were considered regardless of their cell population, IFAT was inferior to isolation in diagnostic efficiency. However, isolation complemented by IFAT resulted in a statistically significant increase in number of positive virus identifications. Under routine working conditions in a large pediatric hospital, it was found that IFAT could not replace isolation techniques but could, if used in conjunction with isolation, provide a significant overall increase in number of positive diagnoses. The time that the specimen was taken in relation to first symptoms was found to be an important variable with respect to the method most likely to succeed in virus identification.