Contribution of a Comparative Western Blot Method to Early Postnatal Diagnosis of Congenital Syphilis

Abstract

Serology has a pivotal role in the diagnosis of congenital syphilis (CS), but problems arise because of the passive transfer of IgG antibodies across the placenta. The aim of this study was to assess the diagnostic value of a comparative Western blot (WB) method finalized to match the IgG immunological profiles of mothers and their own babies at birth in order to differentiate between passively transmitted maternal antibodies and antibodies synthesized by the infants against Treponema pallidum Thirty infants born to mothers with unknown or inadequate treatment for syphilis were entered in a retrospective study, conducted at St. Orsola-Malpighi Hospital, Bologna, Italy. All of the infants underwent clinical, instrumental, and laboratory examinations, including IgM WB testing. For the retrospective study, an IgG WB assay was performed by blotting T. pallidum antigens onto nitrocellulose sheets and incubating the strips with serum specimens from mother-child pairs. CS was diagnosed in 11 out of the 30 enrolled infants; 9/11 cases received the definitive diagnosis within the first week of life, whereas the remaining two were diagnosed later because of increasing serological test titers. The use of the comparative IgG WB testing performed with serum samples from mother-child pairs allowed a correct CS diagnosis in 10/11 cases. The CS diagnosis was improved by a strategy combining comparative IgG WB results with IgM WB results, leading to a sensitivity of 100%. The comparative IgG WB test is thus a welcome addition to the conventional laboratory methods used for CS diagnosis, allowing identification and adequate treatment of infected infants and avoiding unnecessary therapy of uninfected newborns.

FIG 1

Immunological IgG profiles of two mother-newborn pairs evaluated by the comparative WB test. (A) A comparison between an uninfected newborn's serum sample (lane 1) and its mother's sample (lane 2) is shown. No differences between the two specimens are noted. (B) A comparison between an infected newborn's serum sample (lane 1) and its mother's sample (lane 2) is shown. The black arrows on the left indicate the differences showed by the two serum samples. The positions of the four classic diagnostic T. pallidum antigens are indicated on the far right.