MATURATION OF RUBELLA IGG AVIDITY OVER TIME AFTER ACUTE RUBELLA INFECTION

Background: As the incidence of rubella has diminished, the proportion of unspecific rubella IgM reactivity among all samples with rubella I gM reactivity has increased. It is important to distinguish IgM reacti vity caused by primary infection from that caused by reinfection or pe rsistence, especially in pregnant women, as termination of pregnancy s hould be considered when primary rubella is diagnosed during the first trimester. Objectives: To elucidate the changes over time of the avid ity of rubella IgG antibodies after acute rubella infection. Study des ign: Serial samples, 84, were collected from 15 patients up to 4-5 mon ths after acute rubella infection. Rubella specific IgG avidity was te sted by the eluting principle adding 35 mM diethylamine to the washing buffer of a commercially available rubella IgG ELISA. As controls, 13 7 samples from women with remote rubella and 94 samples from patients with a rubelliform rash, were tested. Results: The avidity index incre ased steadily in all patients during the observation time. A low avidi ty index ( < 40%) was seen up to 6 weeks after onset of rash. A high a vidity index ( > 60%) was not observed until 13 weeks after infection and only in four of the 15 patients during the observation time. Concl usions: An increase of rubella IgG antibody avidity was seen during th e whole observation time but was most pronounced during the first 3 mo nths after onset of rash. Measurement of rubella IgG avidity is a good supplemental test for cases with rubella IgM reactivity to confirm or exclude a recent rubella infection. (C) 1997 Elsevier Science B.V.