An IgM capture enzyme linked immunosorbent assay to detect IgM antibodies to treponemes in patients with syphilis

Abstract

A new IgM capture enzyme linked immunosorbent assay (ELISA) was compared with the 19S(IgM) fluorescent treponemal antibody absorption (19S(IgM)FTA-ABS) test for detecting IgM antibodies to treponemes. Serum samples from 180 people, 109 with various stages of untreated syphilis, 45 with treated syphilis, and 26 non-infected, were investigated. In all diagnostic groups of syphilis the reactivity of the IgM capture ELISA was similar to that of the 19S(IgM)FTA-ABS test except in untreated neurosyphilis, for which the IgM capture ELISA was significantly less sensitive. The IgM capture ELISA was very sensitive in congenital (100%, 5/5) and primary (82%, 18/22) syphilis, but less sensitive in secondary (60%, 12/20), latent (53%, 16/30), neurosyphilis (34%, 11/32), and treated (11%, 5/45) syphilis. False positive IgM capture ELISA results were not found in five people who gave false positive Venereal Disease Research Laboratory (VDRL) reactions or in 21 neonates born to mothers adequately treated for syphilis before or during pregnancy. This indicated that the IgM capture ELISA was very specific. The course of antitreponemal IgM reactivity after treatment of early infectious syphilis was followed up in six patients. The quantity of IgM antibody declined in nearly all patients after treatment, but still remained detectable in five patients up to six months after treatment. In contrast, non-treponemal antibodies measured by the VDRL test disappeared in four out of six patients within five months from starting treatment. In conclusion, the IgM capture ELISA may be useful for easy and sensitive detection of IgM antibodies to treponemes in patients with congenital and primary syphilis. A positive test result in these cases indicates that patients should receive treatment if they have not been treated recently. The test is not, however, recommended to replace the VDRL test to monitor patients treated for syphilis.