Comparison of rapid immunofluorescence assay to cell culture isolation for the detection of influenza A and B viruses in nasopharyngeal secretions from infants and children.

In the hospital setting it is often critical to isolate patients appropriately in order to prevent nosocomial infection. This is especially true with respiratory infection in infants and young children. At the present time a rapid immunofluorescence assay (IFA) for respiratory syncytial and parainfluenza viruses is routinely carried out in our laboratory. During January and February of 1990 we used monoclonal antibodies specific for influenza A and B viruses (Baxter-Bartels, Bellevue, WA) in this rapid IFA. 152 samples of NPS were tested by cell culture isolation (CCI) and IFA for the presence of influenza antigens. Twenty-seven samples were positive by both methods, and 114 were negative by both. Three samples were positive by IFA and negative by CCI, while eight samples were positive by CCI and negative by IFA. Five of these eight samples were not positive until 10 to 14 days after inoculation into cell culture, suggesting that the virus inoculum was small. Using CCI as the 'gold' standard, IFA was 90% sensitive and 93% specific. Because of its turn-around time (2-4 h) and acceptable sensitivity and specificity, IFA for influenza viruses will be a routine test in our diagnostic laboratory during the influenza season.