Question
How well do a T. pallidum IgM Western blot assay and a T. pallidum IgM enzyme immunoassay compare to a rapid plasma reagin (RPR) titer of >1:16 as predictors of congenital syphilis in their babies when performed on samples from mothers with syphilis?  

Design
The maternal T. pallidum IgM status was evaluated in a convenience sample of mother-baby pairs with reactive syphilis serology to determine if maternal IgM was more helpful in identifying babies at high risk of congenital infection than a maternal titer of >1:16 by RPR.  The two T. pallidum IgM tests were also evaluated for the identification of babies with congenital syphilis. 

Participants
A sequential sample of 97 mother-baby pairs (96 mothers and 100 babies) with reactive syphilis serology seen at Kings County Hospital in Brooklyn, New York, who had adequate blood samples available for testing were evaluated.  Mothers were eligible if they had a reactive RPR with a reactive confirmatory fluorescent titer antibody-antigen screen at delivery.  Mothers were excluded in they had no detectable T. pallidum IgG antibodies with either of the two methods used.

Description of Tests and Diagnostic Standard
Babies were evaluated for congenital syphilis with a routine physical examination as well as a long bone x-ray of the knee, and lumbar puncture for cerebrospinal fluid (CSF) VDRL testing.  Umbilical, nasopharyngeal, or CSF smears were tested with an immunofluorescent antigen detection method for T. pallidum, if material was available.  Clinical congenital syphilis was defined as the presence of any one or more of the following:  hepatosplenomegaly, rash suggestive of congenital syphilis, characteristic radiographic findings, positive CSF VDRL, a positive fluorescent antibody result, or a reactive FTA-ABS at or after 12 months of age.  

Discarded maternal and infant sera were used for T. pallidum IgM testing by 2 different methods: a Western blot (WB) and an enzyme immunoassay (ELISA).  The WB was performed as previously described (J Infect Dis, 1993;168:238-242). The presence of any band associated with T. pallidum was considered a positive result in babies, and the presence of the 47-kDa band and at least one other T. pallidum band was considered positive for mothers.  The ELISA assay (CAPTIA Syphilis-M, Mercia Diagnostics Ltd., Bradford Park, Surrey, UK) was performed according to the manufacturer’s protocol.  Maternal serum was also tested with a T. pallidum IgG ELISA (Mercia Diagnostics Ltd.) and a T. pallidum IgG WB.  

Main Outcome Measures
The associations between congenital syphilis and an RPR titer >1:16 or a maternal IgM WB-positive test were determined.  

Main Results
Among 32 mothers with RPR titers >1:16.  Five of the 7 babies with congenital syphilis born to T. pallidum WB-positive mothers also had positive IgM WB.  None of the 7 babies with congenital syphilis born to T. pallidum WB-negative mothers were positive by IgM WB.  One baby had a positive IgM WB but no other evidence of congenital syphilis.  

Results of maternal T. pallidum IgM antibody tests and of the diagnosis of congenital syphilis in their 100 babies for 97 women with reactive RPR tests at delivery

Positive maternal T. pallidum IgM WB testing on mothers with reactive RPRs at delivery identified a group of mothers at higher risk of delivering babies with congenital syphilis. The IgM ELISA was not as sensitive as the WB at detecting IgM antibodies in the mothers.  A maternal RPR titer >1:16 was not as useful as the IgM WB in defining the risk of having a baby with congenital syphilis.  However, the performance of the IgM WB in either mothers or newborns was not adequately sensitive to identify all infected babies. 

Source of funding:  Mercia Diagnostics Ltd. provided kits.  

For correspondence:  Sarah A Rawstron, Department of Pediatrics, Box 49, Children’s Medical Center of Brooklyn, SUNY Health Science Center at Brooklyn, 450 Clarkson Avenue, Brooklyn, NY 11203-2098.  E-mail address:  HYPERLINK mailto:sarah.rawstrom@downstate.edu sarah.rawstron@downstate.edu.