DETERMINATION OF IMMUNITY TO MEASLES-VIRUS IN YOUNG-ADULTS - COMPARATIVE-EVALUATION OF A COMMERCIAL ENZYME-IMMUNOASSAY AND THE HEMAGGLUTINATION INHIBITION TECHNIQUES

Background: Determination of the immune status against measles in youn g adults requires careful evaluation of the laboratory methods because of waning immunity. The hemagglutination inhibition (HI) test and enz yme-linked immunosorbent assay (ELISA) may lack the sensitivity requir ed to detect very low levels of antibodies. In addition, the correlati on between ELISA-IgG assays and the degree of protection from measles is not well defined. Objectives: (a) Evaluation of a commonly used mea sles ELISA-IgG test kit in comparison with the hemagglutination inhibi tion (HI) test which corresponds strongly to virus neutralization; (b) determination of false negative rates of the ELISA-IgG and the HI tes ts; (c) evaluation of the ELISA-IgG test kit as a quantitative assay. Study design: One hundred and eighty serum samples collected from 60 v accinated young adults immediately before vaccination and 14 and 28 da ys postvaccination, were tested comparatively by HI and by a commercia l ELISA-IgG kit. For evaluation of false negative rates, postvaccinati on sera of a cohort of 48 vaccinees with negative HI or ELISA-IgG prev accination sera were tested for IgM. Sixty-three of the samples were a lso titrated by the ELISA-IgG kit using serial dilutions, for comparis on with HI titers. Results: Using the HI test as a reference method, t he ELISA-IgG kit was found to have overall accuracy of 81%, sensitivit y of 80% and specificity of 84%. The false negative and the false posi tive rates were 20% and 16%, respectively. In contrast, when we used p ostvaccination IgM test to distinguish between true and false prevacci nation negatives in both the HI and ELISA-IgG tests, we found that the false negative rates were 75.6% by ELISA and 72.5% by HI, and the fal se positive rates were 2.4% and 0%, respectively. Serum titers determi ned by the ELISA-IgG test were generally 5-10-fold higher than the cor responding HI titers, but without a consistent correlation. Conclusion s: Both the ELISA-IgG and the HI tests frequently failed to detect res idual immunity. The two tests also did not correlate well with each ot her suggesting that different antigenic determinants of the virus are involved in each assay and therefore the HI test should not be used as a reference method for evaluation of the sensitivity of ELISA IgG kit s.