A novel and rapid method for determination of rubella virus immunoglobulin G avidity

Abstract number: 1133_84

Eggers M., Enders M., Strobel S., Piche J., Diz I., Enders G.

Objectives:  

Although rare in many industrialised countries, because of the success of vaccination programmes, rubella infection in pregnancy continues to occur where uptake of the vaccine is low and in immigrants of countries with no vaccination programme. As the clinical diagnosis of rubella is unreliable, serological tests are needed for a diagnosis, especially in pregnancy. Diagnosis is usually made by detection of rubella specific immunoglobulin M (IgM). However, in about 2.2% of clinical normal pregnant women investigated by us in prenatal care long persisting IgM antibodies following previous infection or vaccination are detected. Therefore an easy, rapid, and reproducible test to distinguish between long-persisting rubella virus IgM antibodies from IgM antibody response due to a primary infection in early pregnancy is of great importance. The measurement of the avidity of immunoglobulin G (IgG) antibodies has been shown by several investigators to be helpful in identifying or excluding primary rubella infections in pregnant women.

Method:  

In this study, we adapted this serological technique to the VIDAS system (bioMerieux) using 6 M urea as the dissociating agent. A total of 301 serum specimens were tested: 35 control sera, 50 specimens from women with acute infection, 51 serum samples from women with recent vaccination, 100 serum samples with long persisting IgM, 5 sequential sera from a woman with preconceptional vaccination, 10 sera from women with reinfection in pregnancy after vaccination, and 50 serum samples without IgM from women with past infection or vaccination. To evaluate the performance of this novel VIDAS Rubella IgG avidity test we compared it with the diethylamine denaturation (DEA) procedure used in an in-house version of the laboratory Enders since 1998.

Results:  

Our results show that the bioMerieux test is easy to use, and that an avidity index higher than 40% allows the exclusion of a recent infection or vaccination: <20% indicates acute infection or recent vaccination during the last 2 months, 20–40% is considered borderline, and >40% indicates past infection or previous vaccination.

Conclusion:  

This new VIDAS rubella IgG avidity assay is a rapid (50 min), reproducible test with very good performance and is of considerable practical value for decision on the need of prenatal diagnosis, to avoid requesting too many follow up sera and, most important, in preventing unnecessary termination of pregnancy.