[Current developments in the laboratory diagnosis of rubella]

Thirty years after the introduction of the hemagglutination inhibition assay (HAI), laboratory diagnosis of rubella virus infection has achieved a high reliability. While the HAI remains the reference standard against which newer assays are compared, routine laboratory diagnosis is based mainly on ELISA tests which permit a more rapid and less cumbersome detection of specific IgG and IgM antibody. Although quantification of immunoglobulin G against rubella virus is performed using WHO standards, the correlation between different ELISAs is relatively poor. Despite substantial improvements in virus isolation and nucleic acid amplification techniques, serology remains the mainstay of diagnosis for both acquired and postnatal diagnosis of congenital infection. Differentiation between primary and re-infection is of critical importance during pregnancy and can be achieved relatively reliably by antibody avidity determination or by immunoblot. While current anti-rubella IgM ELISAs are relatively sensitive, their specificity may be limited by cross reactivity with other viruses, i.e. parvovirus B19 and Epstein-Barr virus. Maternal reinfection with congenital rubella syndrome is very rare, however it may be misdiagnosed in the absence of significant IgG antibody titer change and/or IgM antibody.