Relationship of IgG avidity index and IgM levels for the differential diagnosis of primary from recurrent cytomegalovirus infections.

Since the incidence of symptomatic congenital cytomegalovirus infection is low (~0.05%) and risk factors are not well defined, it is difficult to develop strategies for prevention. The aim of this study was to recognise the utility of specific Immunoglobulin G avidity analysis for distinguishing primary infection from past/recurrent infection. Sera from 50 women with cytomegalovirus specific Immunoglobulin M antibodies without proven seroconversion and infants born to these women were tested for presence of Immunoglobulin M antibodies by commercial enzyme immunoassay. For cytomegalovirus specific immunoglobulin G avidity, sera were measured by commercial kit according to manufacturer's recommendations. Among 50 sera form mothers, 26 showed the presence of Immunoglobulin M antibodies out of which 15 had low avidity antibodies. Out of 50 sera from children, 18 showed the presence of Immunoglobulin M antibodies. Out of these 18 sera from children, 12 were symptomatic, which all showed the presence of low avidity antibodies. The results showed that an avidity index <40% and presence of Immunoglobulin M antibodies is highly suggestive of a recent primary infection.