APPLICATION OF ELISA FOR IGM, IGA AND ANTIGEN-DETECTION FOR RAPID DIAGNOSIS OF RESPIRATORY SYNCYTIAL VIRUS-INFECTIONS - A COMPARATIVE-STUDY

Background: Infection with Respiratory Syncytial Virus (RSV) can be ra pidly diagnosed by detection of viral antigen in nasopharyngeal secret ions (NPS) or serologically by detecting IgM and IgA antibodies. Objec tives: To evaluate the above methods for reliability and rapidity, and compare them with the complement fixation (CF) test and virus isolati on. Study design: Viral antigen was tested in 145 NPS samples by ELISA in parallel with tissue culture isolation. The geometric mean titer ( GMT) of complement fixing antibodies in various age groups was determi ned from 92 individual serum samples by CF test. The diagnostic method s, CF test, ELISA-IgM and ELISA-IgA, were evaluated using 21 pairs of acute and convalescent sera. Appearance of IgM and IgA in serum sample s with low or negative CF titers was studied in two age groups: 0-10 m onths (n=82), and 11 months-9 years (n=47). Results: From the 145 NPS samples, 20 samples were positive by both ELISA and virus isolation, 9 were positive only by ELISA and 5 were positive only by virus isolati on. The GMT by age group for 92 sera evaluated by CF test were 40 (0-1 0 months), 195 (11-24 months), 269 (2-4 years), 173 (5-12 years) and 1 32 (adults). Among the 21 paired sera examined, CF test detected 13 RS V infections by antibody rise or seroconversion while the ELISA-IgM/Ig A tests identified all 21 infections, 7 of them in the first sample. T he presence of IgM alone or IgM and IgA antibodies was demonstrated in both age groups examined; however, IgA alone was found only in the ag e group 11 months and older. Conclusions: ELISA for antigen detection is better than virus isolation because it is faster (6-20 h vs. 3-20 d ays, respectively) and more sensitive (29/34 vs. 25/34 positives, resp ectively). ELISA-IgM and ELISA-IgA was more sensitive and reliable tha n the CF test, particularly for the 0-10 month age group. Thus, when n ecessary, serological diagnosis of RSV infection can be based on the p resence of IgM and/or IgA antibodies in serum samples obtained early a fter onset of symptoms.