The late detection of respiratory syncytial virus in cells of respiratory tract by immunofluorescence.

Paired nasopharyngeal secretions were studied in 27 infants infected with respiratory syncytial virus, one taken at onset of illness and one about 7 days later. Both specimens were examined by immunofluorescence and tissue culture for respiratory syncytial virus. In 25 out of 27 (93%) specific fluorescence was still present in cells of the convalescent specimen but was much duller. Virus was difficult to isolate in convalescent specimens; only 8 out of 27 (26%) proved to be positive. Eight single secretions which were taken late in a respiratory illness were also shown to have this altered fluorescence with absence of virus isolation. Preliminary experiments using antihuman globulin suggest that the findings may be due to the attachment of local secretory antibody to the cells causing ;blocking' of staining reaction.