Changing patterns of detection of viruses in respiratory specimens since introduction of monoclonal antibody-based immunofluorescence test for respiratory syncytial virus antigen

In our earlier studies, a rapid monoclonal antibody-based direct immunofluorescence (IF) test for respiratory syncytial virus (RSV) antigen in nasopharyngeal aspirates (NPAs) proved sensitive and specific, and dual virus infections were very rare when the test was used during the winter RSV season. We therefore recommended that virus isolation in cell culture be restricted to RSV antigen-negative specimens when RSV infection was highly prevalent (October to March in the UK). We reviewed the effect of this policy on the detection of RSV and other viruses in NPAs. The number of NPAs received each RSV epidemic increased markedly with time (3804 in 1984–88, 4569 in 1989–93, P < 0.0001), while during the test of the year the numbers declined slightly (753 vs. 700 for the same periods, P < 0.05). The RSV positivity rate increased October to March (1447/3588 (40%) in 1984–89, 2357/4591 (48%) in 1989–94, P < 0.0001). Restricted use of virus isolation led to a dramatic decline in the yield of RSV in cell culture from RSV IF-negative NPAs (196/3804 (5.2%) for 1984–88, 30/4569 (0.66%) for 1989–93, P < 0.0001). The already low yield on non-RSV respiratory viruses in cell culture was not affected by this policy. A strategy is proposed for the detection of RSV and other respiratory viruses in NPAs which may make virus isolation on such specimens obsolete.