Reliability of low-avidity IgG and of IgA in the diagnosis of primary infection by rubella virus with adaptation of a commercial test

Abstract

The detection of IgA and low-avidity IgG and antibodies in serum is a potentially useful marker of recent infection by a microorganism. We studied the reliability of IgG avidity and presence of IgA for the diagnosis of recent acute infection by rubella virus. Low-avidity IgG (Avy-EIA test) was determined with a modified commercial test using 8 molar urea (indirect ELISA, DiaSorin, Italy) and IgA was determined with a homemade indirect ELISA test. Twenty-five patients with recent primary infection by rubella virus (group I) and 50 healthy subjects (group II) were studied. In group I low-avidity IgG varied between 100 and 0% (67.3 ± 21.8%); IgA was present in 24 patients (96%). In group II low-avidity IgG varied from 50.4 to 0% (19.8 ± 16.9%). IgA was present in 2 subjects (4%). The sensitivity of the Avi-EIA and the IgA test was 92 and 96%, respectively; specificity was 100 and 96%, respectively. We conclude that both low-avidity IgG and IgA tests are helpful and reliable for the diagnosis of recent primary infection.

HCV avidity as a tool for detection of recent HCV infection: Sensitivity depends on HCV genotype

“…For example, for the analysis of very recent infection (time since infection of <8 weeks), some individuals may have been infected up to 16 weeks previously. The chaotropic agent used in an avidity assay can also affect the AI cut‐off and mean duration of recent infection; therefore, a switch to different chaotropic agents may reduce the genotype effect.…”

Distinguishing between primary infection and reinfection with rubella vaccine virus by IgG avidity assay in pregnant women

“…When the prevalence of rubella is low, such as in countries with high rubella vaccination coverage, the positive predic-tive value of IgM testing decreases such that there is a significant risk of false positive results, and additional confirmation tests are therefore required [5, 15,25]. The measurement of rubella-specific IgG avidity is a specific and sensitive method for the serological diagnosis of recent primary infection, and provides the distinction between primary infection and possible reinfection [15,18].…”

“…Therefore, detection of IgM alone cannot differentiate primary infection from reinfection. For these cases, the measurement of IgG avidity is very useful, since, in the case of recent primary infection, IgG is low-avidity and in the case of reinfection, IgG is high-avidity [15,18,24,28,29].…”

“…The avidity of IgG for rubella virus was measured by a protein-denaturing EIA where the antibodies were first allowed to bind to the rubella virus antigen, followed by elution by buffer with and without 35 mM diethylamine [15,18,19]. Each sample was tested at 2 replicates and a single serum dilution (1:200) was applied to each replicate.…”