Value of IgG avidity in cytomegalovirus infrection diagnosis in pregnant women and newborn infants

Aim: To asses the value of IgG avidity in diagnosis of CMV infection in pregnant women and newborn infants. Methods: During the three-year period (2003-2005) serum samples from 64 pregnant women and 32 infants less than 12 months of age with suspected congenital/perinatal CMV infection were collected. Sera were tested for CMV IgM and IgG using an indirect enzyme-linked immunosorbent assay and IgG avidity using urea as denaturing agent. Results: Among IgM positive women, 2/26 (7.6%) showed an increase of IgG avidity index (AI) from intermediate to high AI in paired sera samples indicating recent primary infection and 24/26 (92.4%) showed high AI indicating past infection. All women with negative IgM antibodies had high AI. In infants less than 12 months of age, acute/recent primary CMV infection was documented in 8/12 (66.7%) children with positive IgM and in 10/20 (50.0%) children with negative IgM antibodies. In two children less than three months with high AI, CMV infection was confirmed by virus isolation from urine. One of them showed a decrease of AI from high to low in paired sera samples. Conclusions: IgG avidity differentiates primary from nonprimary CMV infection in both pregnant women and infants older than three months. In children less than 3 months of age, transplacentally transferred maternal antibodies of high avidity may influence on the serologic test results.