Rubella screening and vaccination programme at a Melbourne maternity hospital. A five-year review

Standardization of Assays That Detect Anti-Rubella Virus IgG Antibodies

Rubella virus usually causes a mild infection in humans but can cause congenital rubella syndrome (CRS). Vaccination programs have significantly decreased primary rubella virus infection and CRS; however, vaccinated individuals usually have lower levels of rubella virus IgG than those with natural infections. Rubella virus IgG is quantified with enzyme immunoassays that have been calibrated against the World Health Organization (WHO) international standard and report results in international units per milliliter. It is recognized that the results reported by these assays are not standardized. This investigation into the reasons for the lack of standardization found that the current WHO international standard (RUB-1-94) fails by three key metrological principles. The standard is not a pure analyte but is composed of pooled human immunoglobulin. It was not calibrated by certified reference methods; rather, superseded tests were used. Finally, no measurement uncertainty estimations have been provided. There is an analytical and clinical consequence to the lack of standardization of rubella virus IgG assays, which leads to misinterpretation of results. The current approach to standardization of rubella virus IgG assays has not achieved the desired results. A new approach is required.

Investigation into low-level anti-rubella virus IgG results reported by commercial immunoassays

Since the 1980s, commercial anti-rubella virus IgG assays have been calibrated against a WHO International Standard and results have been reported in international units per milliliter (IU/ml). Laboratories testing routine patients' samples collected 100 samples that gave anti-rubella virus IgG results of 40 IU/ml or less from each of five different commercial immunoassays (CIA). The total of 500 quantitative results obtained from 100 samples from each CIA were compared with results obtained from an in-house enzyme immunoassay (IH-EIA) calibrated using the WHO standard. All 500 samples were screened using a hemagglutination inhibition assay (HAI). Any sample having an HAI titer of 1:8 or less was assigned a negative anti-rubella virus antibody status. If the HAI titer was greater than 1:8, the sample was tested in an immunoblot (IB) assay. If the IB result was negative, the sample was assigned a negative anti-rubella virus IgG status; otherwise, the sample was assigned a positive status. Concordance between the CIA qualitative results and the assigned negative status ranged from 50.0 to 93.8% and 74.5 to 97.8% for the assigned positive status. Using a receiver operating characteristic analysis with the cutoff set at 10 IU/ml, the estimated sensitivity and specificity ranged from 70.2 to 91.2% and 65.9 to 100%, respectively. There was poor correlation between the quantitative CIA results and those obtained by the IH-EIA, with the coefficient of determination (R(2)) ranging from 0.002 to 0.413. Although CIAs have been calibrated with the same international standard for more than 2 decades, the level of standardization continues to be poor. It may be time for the scientific community to reevaluate the relevance of quantification of anti-rubella virus IgG.

Evaluation of eight anti-rubella virus immunoglobulin g immunoassays that report results in international units per milliliter

An evaluation of anti-rubella virus immunoglobulin G (IgG) immunoassays that report in international units per milliliter (IU/ml) was performed to determine their analytical performance and the degree of correlation of the test results. A total of 321 samples were characterized based on results from a hemagglutination inhibition assay. The 48 negative and 273 positive samples were used to determine the sensitivity and specificity of the assays. When equivocal results were interpreted as reactive, the sensitivity of the immunoassays ranged from 98.9 to 99.9% and the specificity ranged from 77.1 to 95.8%. All assays had positive and negative delta values of less than 2. A significant difference between the mean results of all assays was demonstrated by analysis of variance. However, post hoc analysis showed there was good correlation in the mean results expressed in IU/ml between some of the assays. Our results show the level of standardization between anti-rubella virus IgG immunoassays reporting results expressed as IU/ml has improved since a previous study in 1992, but further improvement is required.

Multicenter evaluation of a novel quantification method for rubella and toxoplasmosis antibodies

Antibody quantification by EIA is possible without a standard curve. Following the so-called alpha method only one test dilution is used, the resulting absorbance is corrected and the IU/ml will be calculated by means of a mathematical formula. This new kind of a single point measurement was evaluated in seven independent laboratories by comparison with commercial EIAs using a standard curve or a titer calibration line. For the quantification of IgG against rubella virus this study comprised 1,480 individual samples and three comparison EIAs. For IgG against Toxoplasma gondii a total of 743 samples was evaluated in two comparison tests. The results obtained by the alpha method show a precision and accuracy more than sufficient for routine testings. Also the technical expenses and reagent costs were reduced. Prerequisites and limitations are discussed against the background of the problem of immune status definition.

Multicenter evaluation of five commercial rubella virus immunoglobulin G kits which report in international units per milliliter

In a multicenter study, the consistency of international units expressed by five commercially available rubella virus immunoglobulin G kits was evaluated. The linearity and within-run and between-run precision were determined for each kit. All kits demonstrated good linearity and had within-run and between-run precision coefficients of variation ranging from 5.1 to 21.7% and from 9.5 to 51.0%, respectively. To compare the international units expressed, the results from 40 samples tested in duplicate were compared with the results of a reference enzyme immunoassay calibrated with World Health Organization international standard serum and a hemagglutination inhibition test. The results of the kits were plotted against those of the reference tests, and linear regression analysis was applied. The Pearson correlation coefficient ranged from 0.64 to 0.75 when the commercial kit results were compared with those of the reference enzyme immunoassay, indicating only a moderate degree of correlation. Therefore, the international units expressed by the commercial kits are insufficiently consistent to be of practical use in diagnostic clinical microbiology.

Is primary cytomegalovirus infection an occupational hazard for obstetric nurses? A serological study

The results are reported of a 4-year prospective study of the incidence of primary cytomegalovirus (CMV) infection in the nursing staff of a specialist obstetric hospital. The absence of seroconversion found in personnel attending patients with confirmed CMV-infection justifies reassuring staff members in "high-risk" areas of the adequacy of the methods used to combat cross-infection. On the other hand, a low rate of seroconversion (1.2% per annum) in the staff who nurse normal mothers and "rooming-in" babies emphasizes the need for the rigorous observance of hygienic precautions by all personnel in all areas. The results of this Australian investigation are discussed in relation to the northern hemisphere experience of CMV-seroconversion in pediatric nurses.

Congenital rubella syndrome in Western Australia

The birth prevalence of congenital rubella syndrome (CRS) in Western Australia has been around 20 per 10 000 live births with peaks up to 100 per 10 000 in rubella epidemic years. The rate appears to be falling but it is still too soon to know whether the rubella vaccination programme in Western Australia has made a significant impact. The cohorts of young women who would have received the schoolgirl vaccination programme are only now entering the child bearing age groups. Observed falls may be due also to delayed diagnosis particularly of cases of deafness only. The proportion of nonimmune young women who would have been eligible for the programme in one maternity hospital has fallen. This study needs to be repeated to ascertain whether further epidemics of rubella have resulted in peaks of CRS or whether the vaccination programme has started to have an effect.

Impact of rubella vaccination in Australia

Rubella vaccination of schoolgirls aged 10-14 years started 13 years ago in Australia; the girls were vaccinated without prior assessment of their immunity. Non-pregnant seronegative women were also offered vaccination in family-planning clinics and post partum in obstetric units. Serological follow-up of 191 schoolgirls 5 years after vaccination and 56 girls 8 years after vaccination showed that all had detectable rubella antibody, whereas 24% of 239 unvaccinated young men of similar age (18-23 years) were seronegative. In 1983, 96% of 8226 pregnant women aged 12-53 years (mean 25.3 years) had detectable rubella antibody, and since 1977 there has been a striking reduction in the incidence of deafness due to congenital rubella. These results indicate that the rubella vaccination programme in Australia is having a significant impact on both the serological status of pregnant women and on the incidence of congenital infection.