Enzyme-linked immunosorbent assays for detection of immunoglobulin M to nontreponemal and treponemal antigens for the diagnosis of congenital syphilis

Abstract

Sera from newborn infants born of mothers with a high risk of syphilis were examined for immunoglobulin M (IgM) antibodies in two different enzyme-linked immunosorbent assays (ELISAs), using either purified flagella from Treponema phagedenis biotype Reiter or the Venereal Disease Research Laboratory (VDRL) antigen as the antigen. All sera were also examined by the fluorescent treponemal antibody absorption (FTA-ABS) test for IgM. Three different groups of patients were studied. Group 1 consisted of 84 women and their newborn infants from a high-risk population for syphilis. Congenital syphilis was diagnosed in one child who had an IgM-positive cord blood specimen in both the ELISA and the FTA-ABS test. Group 2 consisted of 10 mothers and their newborn children. All mothers had positive syphilis-screening tests, and all children had signs of congenital syphilis. All but one child had positive IgM tests. Group 3 consisted of 15 mothers and their newborn children. These mothers had been treated for syphilis late in pregnancy, and all had a positive screening test at delivery. Two of the children had positive IgM tests, probably caused by reactivity after late intrauterine treatment of congenital syphilis. The specificities of the IgM tests were high when evaluated with sera from newborn children without signs of congenital syphilis. Even though IgM rheumatoid factor was found in all of the children tested with definite congenital syphilis, the rheumatoid factor did not cause false-positive results in either the VDRL ELISA or the flagellum ELISA. No significant IgG-IgM competition was noticed in the ELISAs. This study also confirmed that IgA antibodies do not cross the placenta; most newborn children with congenital syphilis were positive in the VDRL ELISA for IgA. Both the VDRL ELISA and the flagellum ELISA are very useful in the diagnosis of congenital syphilis and may be substitute for the FTA-ABS test. The VDRL ELISA for IgM will be especially useful in developing countries with a high incidence of congenital syphilis.