Enzyme-linked immunosorbent assay to assess respiratory syncytial virus concentration and correlate results with inflammatory mediators in tracheal secretions

Objective. We developed an enzyme-linked immunosorbent assay (ELISA) for the quantitation of respiratory syncytial virus (RSV) in respiratory secretions in intubated patients infected with RSV. Methods. We compared the quantitative ELISA and a standardized plaque assay in intubated children <2 years of age who were mechanically ventilated for severe RSV disease and enrolled in a randomized double blind placebo-controlled treatment trial of a monoclonal antibody to the F protein of RSV (palivizumab; Synagis). We also examined the relationship between the concentrations of virus as measured by ELISA and of three inflammatory indices in respiratory secretions (white blood cell count, myeloperoxidase and eosinophilic cationic protein). Results. Quantitative ELISA and plaque assay were highly correlated for both tracheal aspirates (r = 0.67, P = 0.001) and nasal wash specimens (r = 0.75, P = 0.001). Treatment with palivizumab significantly neutralized RSV in tracheal aspirates as measured by plaque assay. In contrast quantitation of RSV by ELISA was not affected by palivizumab treatment. This finding is consistent with results that were obtained in preliminary studies of RSV- containing media treated with monoclonal antibody, where we found that the ELISA measured virus whether antibody-bound or not. The inflammatory indices were not correlated with RSV concentration measured by ELISA or plaque assay. Conclusions. We conclude that this quantitative ELISA is a potentially useful tool for measurement of RSV concentration in respiratory secretions that may help elucidate the pathophysiology of acute RSV infection. Specific antiviral strategies for the treatment of RSV disease could be evaluated by this method.