AVIDITY OF IGG ANTIBODIES DISTINGUISHES PRIMARY FROM NONPRIMARY CYTOMEGALOVIRUS-INFECTION IN PREGNANT-WOMEN

Background: Human cytomegalovirus (HCMV) is the most common cause of v iral intrauterine infection. Fetal damage is mostly linked to maternal primary infection. It is therefore important to differentiate primary from non-primary infection in pregnant females. IgM tests often used for this purpose are not reliable enough. Objective: To evaluate an HC MV-IgG urea-elution assay for its ability to distinguish primary from non-primary infection. In this assay, soaking the antigen-antibody com plex with an urea containing solution frees antibodies with low avidit y but has no influence on those with high avidity. An avidity index (A I) was calculated: AI = (OD with urea/OD without urea) x 100. Study de sign: HCMV-IgG avidity was measured on a single serum of 79 patients w ith past infection (pregnant women, graft recipients and blood donors) and of 63 patients (78 sera) with documented seroconversion (pregnant women and graft recipients). Sixty-one pregnant women positive or equ ivocal for HCMV-IgM but without a documented seroconversion were inclu ded in this study. Results: Most (72/79) of the patients with past inf ection had an AI > 65% and all but one had an AI > 50%. In pregnant wo men, in the case of a primary infection within the past 3 months, AI a re usually (51/53)< 50% and never > 65%. Among the IgM positive pregna nt women who lack a seroconversion history, 38 had AI > 65% suggestive of an infection that had occured at least 3 months earlier, 11 had an AI in a grey area between 50 and 65% and 12 had an AI < 50%, suggesti ve of a recent primary infection. Conclusions: In pregnant women, meas urement of the IgG avidity may help to date a HCMV infection, an AI > 65% highly suggests a past infection while an AI < 50% corresponds to a recent primary infection. (C) 1998 Elsevier Science B.V. All rights reserved.