RESUMEN
The serological response to respiratory syncytial virus (RSV) in 125 pediatric patients hospitalized with acute lower respiratory infection was investigated by enzyme linked immunosorbent assay (ELISA) for specific immunoglobulin (Ig) A, IgG, and IgM and complement fixation (CF) test. By ELISA, a 4-fold rise in IgG titre in paired sera was most commonly found, followed by a rise in IgA and IgM titres. Investigation by ELISA and CF leads to the suggestion that major CF activity against RSV antigens resides in the IgG and not the IgA and IgM classes. No case with CF activity failed to be diagnosed by ELISA. The youngest infant who could develop seroconversion was one month old, nevertheless two children older than two years could not. When the three diagnostic methods were compared, ELISA serology was the most sensitive followed by indirect immunofluorescence (IIF) for antigen detection and virus isolation, respectively, ELISA could diagnose RSV infection in 45% of the study cases, whereas IIF and virus isolation only diagnosed 26% and 14%, respectively. Half of the cases was diagnosed by all of the three methods together.