Combination of microneutralization and avidity assays: Improved diagnosis of recent primary human cytomegalovirus infection in single serum sample of second trimester pregnancy

Abstract

Estimation of IgG avidity index is a classical serological method. Antibodies with low avidity are detectable at a very early stage of infection whereas high avidity antibodies indicate past infection. Recently, it was shown that the neutralization assay can be routinely used as a reliable method for differentiating between acute primary and non-primary infection in a single serum sample because the first neutralizing titers (NT) appeared after an average of 13 weeks (range, 10-17 weeks). A low positive NT titer in the presence of specific IgM antibodies, however, still represents a diagnostic problem especially if blood sampling occurred after the 12th week of gestation. To overcome this problem the combination of NT and IgG avidity tests was evaluated. Human cytomegalovirus (HCMV) IgG avidity indices of 350 serum samples from 227 pregnant women were investigated using 6M urea in the washing buffer. HCMV specific IgG antibodies reached full maturation approximately 20-22 weeks after seroconversion and low IgG avidity is therefore a marker of primary infection. The combined application of the microneutralization and avidity assays was shown to serve as a helpful tool in diagnosis of a recent primary HCMV infection of second trimester pregnancy particularly when previous serological data were not available.

Precision and Accuracy of a Procedure for Detecting Recent Human Immunodeficiency Virus Infections by Calculating the Antibody Avidity Index by an Automated Immunoassay-Based Method

“…Differently from the detuned assay, this method is quantitative and allows the level of antibody avidity to be determined as a continuous variable, which ranges from 0 to 1 depending primarily on the time elapsed from infection. Moreover, as for the other commonly used avidity assays (1,5,9), the AI is calculated by the ratio of two measures obtained at the same time using the same testing kit, thus eliminating interlot variation.…”

“…The AI is a marker of recent primary infection and is routinely used for several infectious diseases, including toxoplasmosis, rubella, and cytomegalovirus infection (1,5,9). Moreover, it has been applied for a number of other infectious agents, such as hepatitis C virus, hepatitis B virus, human herpes viruses 6 and 7, and varicella-zoster virus (6,17,18,19).…”

Evaluation of an in-house specific immunoglobulin G (IgG) avidity ELISA for distinguishing recent primary from long-term human cytomegalovirus (HCMV) infection

“…These authors showed that sera from women with a past or secondary HCMV infection had an avidity index > 60%, whereas most of the sera from women with HCMV primary infection had avidity index < 50%. In a similar study, using 6 M urea as dissociating agent, EGGERS et al 7 defined avidity indices of < 40% and > 60% as indicative of acute primary and past HCMV infection, respectively. In a study of sera from pregnant women who had recently seroconverted following primary HCMV infection (within four months of the last negative sample) and of sera from individuals with long-term HCMV infection, PRINCE & LEBER 16 showed that 99% of the acute-phase serum samples had avidity indices < 50%, whereas 96% of serum samples from persons with past infection had avidity indices > 60%.…”

“…Based on the observation that antibody avidity gradually increases after exposure to an immunogen 8,23 , several reports have shown that the avidity of IgG antibodies can be used as a marker for distinguishing recent primary from long-term infections, including HCMV infections [2][3][4]7,9,16 .…”

Evaluation of a Cytomegalovirus Glycoprotein B Recombinant Enzyme Immunoassay To Discriminate between a Recent and a Past Infection

“…No "gold standard" assay and no reference test exist for the detection of primary CMV infection. Different approaches (microneutralization, Western blotting, or avidity assays) were developed to differentiate between recent and past CMV infection (2,4,5,8,9). Avidity assays for distinguishing CMV primary infection (with low-avidity IgG antibody) from CMV secondary infection (with high-avidity IgG antibody) are the most widely used techniques (2,6,10,14).…”