Rapid diagnosis of respiratory syncytial virus and influenza A virus infections by immunofluorescence: experience with a simplified procedure for the preparation of cell smears from nasopharyngeal secretions.

A simplified procedure for preparing direct smears of exfoliated cells from nasopharyngeal secretions is presented. The specimens were examined by the indirect immunofluorescence (IF) technique for the presence of respiratory syncytial (RS) virus and influenza A virus antigens. Specimens from 457 children hospitalised at twelve different hospital departments in Norway were examined during the winter season 1980-81. RS virus was identified in samples from 139 children and influenza A virus from 28. Results of IF examinations for RS virus were copositive with serology in 19 of 23 cases (83%) and with probably no false positive results. Samples from 29 children were also prepared by the conventional washing technique. RS virus was identified in 18 of these specimens. Seventeen of these were also found positive by the simplified method. This comparison was done blind. Compared to results of virus isolation and serology the IF examinations for influenza A virus were somewhat less sensitive with copositivity in 12 of 17 cases (71%) and in one instance the IF finding was probably false positive. However, also for influenza A virus our IF findings were fully comparable with figures obtained by others who performed the conventional washing technique for preparation of exfoliated cells from nasopharyngeal secretions. General practitioners submitted samples from 65 patients, and RS virus and influenza A virus were identified in eleven and four cases respectively. The simplicity of preparation of cell smears from nasopharyngeal secretions with our simplified method opens up the possibility of the application of rapid respiratory virus diagnostic service to an increasing number of hospital departments and also for general practitioners. We feel that this method is a suitable tool for surveillance of certain respiratory virus infections.