A Novel Point-of-Care Rapid IgM Test for the Diagnosis of Congenital Syphilis

Neonatal syphilis-specific IgM immunoglobulins are fetal in origin and may reflect congenital syphilis. This pilot study aims to determine the test performance of a point-of-care antitreponemal IgM test for the diagnosis of congenital syphilis.

Sera from 2 uninfected and 29 pregnant patients with syphilis and 8 of their newborns with sonographic evidence of congenital syphilis were collected between May 2022 and June 2024. Duplicate 20 μL serum aliquots were tested using a research-use-only point-of-care lateral flow test developed by Diagnostics Direct, LLC (Stone Harbor, NJ) for the detection of antitreponemal IgM. Duplicate 50 μL serum aliquots from the samples were tested for treponemal IgM using 2 Commune-Europe-marked immunoblot tests as comparators (ViraMed, Planegg, Germany, and Euroimmun, Lübeck, Germany) and a commercial IgM ELISA (Euroimmun). The composite IgM reference comparator was based on these 3 tests. If at least 2 of 3 were positive, this was considered a positive reference comparator, and 2 negative test results constituted a negative comparator. Mother-baby dyads were staged for syphilis according to national guidelines.

The positive percent agreement of the point-of-care test was 93% (confidence interval [CI], 68.0%-99.8%), and the negative percent agreement was 88% (CI, 87.5CI-97.3%) versus the composite IgM reference comparator. Based on combined maternal and infant clinical diagnosis, the positive percent agreement was 100% (73.5%-100%), and the negative percent agreement was 82% (CI, 61.9%-93.7%).

The syphilis point-of-care IgM test demonstrated very good preliminary test performance when compared with a composite reference comparator and specimens collected from mother-baby dyads. Further studies evaluating this point-of-care antitreponemal IgM test as a neonatal diagnostic test for congenital syphilis are warranted.