Primary postnatal Rubella infection is typically a mild self-limiting disease characterized by a macropapular rash, fever, malaise and lymphadenopathy. In contrast to postnatal infections, primary prenatal infections may have devastating effects. In utero infections may severely damage the fetus, particularly if occurring during the first four months of gestation. The congenitally infected infant may exhibit one or more of a variety of defects collectively known as the Congenital Rubella Syndrome (CRS). Among these are low birth weight, cataracts, deafness, congenital heart disease and mental retardation.
Since Rubella does not have typical symptomatology, the clinical picture can be quite variable. The disease is often difficult or impossible to diagnose from symptoms alone. The ability to detect the IgM class of anti-Rubella antibody in a single sample overcomes some of the problems associated with paired sera analysis of specific IgG and provides a clearer serodiagnosis picture.
A primary infection is associated with the pronounced IgM antibody response to the Rubella virus. In cases of acute primary infection during pregnancy, IgM has been detected 4 to 15 days after appearance of the rash in nearly 100% of the cases. IgM levels begin to decline after 36 to 70 days, and are infrequently detected after 180 days. IgM antibody reactive with Rubella virus has been observed following reinfection, however, the levels are low and not detectable by all IgM assays. Such asymptomatic reinfection of immune pregnant women, generally believed to be harmless to the fetus, is characterized serologically usually only by a significant rise in IgG antibody titer.
Although the clinical utility of Rubella IgM detection is usually associated with testing pregnant women, testing of nonpregnant individuals for IgM antibodies to Rubella virus is a useful aid in diagnosis of acute infection. In situations where primary infection is suspected, the optimum time for specimen collection has been reported to be 1 to 2 weeks after the onset of the rash. Reactivity for IgM antibodies to Rubella may indicate current infection, reactivation or recent vaccination.
Manufacturer’s Reagent package insert Architect Rubella IgM, May 2017, Abbott Ireland Diagnostics Division, Finisklin Business Park, Sligo, Ireland.