Multicenter evaluation of a rapid and convenient method for determination of cytomegalovirus immunoglobulin G avidity

An easy, rapid, and reproducible test to distinguish residual cytomegalovir us (CMV) immunoglobulin M (IgM) antibodies from antibodies produced in prim ary infection could be useful, especially for pregnant women. The CMV avidi ty of IgG antibodies with the VIDAS automated enzyme-linked fluorescent ass ay and 6 M urea was evaluated in a multicenter study to differentiate betwe en primary CMV infections and past infections or reactivations. A total of 416 serum specimens were tested: 159 specimens were from follow-up of prima ry infections, and 257 were from past infections. All of the specimens from primary infections collected within 4 months (17 weeks) after the onset of the infection had an avidity index lower than 0.8, An avidity index higher than 0.8 excludes a recent primary infection of less than 4 months. Howeve r, an avidity index higher than 0.8 cannot confirm all past infections, sin ce 48 specimens (18%) from past infections had an avidity index lower than 0.8 (between 0.5 and 0.8). The exclusion capacity could be improved (96.9%) by using a cutoff of 0.7, but this index would decrease the specificity of the technique, since the avidity index was found to be between 0.7 and 0.8 in two patients with recent primary infection. All specimens from primary infections obtained more than 4 months after the onset of infection had an avidity index more than 0.2. In this study, an avidity index less than 0.2 confirms the presence of a recent primary infection of less than 4 months. The VIDAS CMV IgG avidity test is a rapid, reproducible test, with very goo d performance.