From the Guidelines
The best way to evaluate for congenital syphilis infection on follow-up in an infant is through serial serologic testing using quantitative nontreponemal tests (such as RPR or VDRL) at 3,6, and 12 months of age, or until the tests become nonreactive, as recommended by the most recent guidelines 1.
Key Considerations
- Treponemal tests should not be used to evaluate treatment response because the results for an infected child can remain positive despite effective therapy 1.
- Passively transferred maternal treponemal antibodies can be present in an infant until age 15 months, and a reactive treponemal test after age 18 months is diagnostic of congenital syphilis 1.
- If the nontreponemal test is nonreactive at 18 months, no further evaluation or treatment is necessary, but if it remains reactive, the infant should be fully reevaluated and treated for congenital syphilis 1.
Follow-Up and Treatment
- Infants with initially abnormal CSF findings should have repeat CSF examinations every 6 months until results normalize 1.
- Clinical follow-up should include regular assessments for signs of congenital syphilis such as hepatosplenomegaly, rash, pseudoparalysis, or developmental delays.
- Retreatment with a 10-day course of aqueous crystalline penicillin G (200,000-300,000 units/kg/day IV, administered as 50,000 units/kg every 4-6 hours) may be necessary if the nontreponemal test remains reactive or if there are signs of active infection 1.
Prioritizing Morbidity, Mortality, and Quality of Life
- The approach prioritizes the decline and disappearance of nontreponemal antibodies in uninfected infants, while persistent or increasing titers indicate active infection requiring intervention, thus minimizing morbidity and mortality while improving quality of life 1.
From the Research
Evaluation of Congenital Syphilis Infection
To evaluate for a congenital syphilis infection on follow-up in an infant, several methods can be employed:
- Detection of specific IgM is currently the most sensitive serological method, and the presence of specific IgM should be considered as evidence of a congenital T. pallidum infection 2
- Serial post-partum tests of antibody kinetics can also be used to confirm or exclude suspected cases 2
- Fluorescent treponemal antibody absorption (FTA-ABS) test can be used, but a reactive FTA-ABS after the age of 12 months is not always indicative of congenital syphilis 3
- Combination of Treponema pallidum-specific IgM detection with immunofluorescent antigen detection for T. pallidum can be used to make a diagnosis of congenital syphilis 4
Follow-up Tests
Follow-up tests can be performed to assess the outcome of congenital syphilis:
- Serum venereal disease research laboratory (VDRL) test can be used to monitor the response to treatment, but it may be negative at birth in some cases and become positive after the second day 5
- Cerebrospinal fluid (CSF) examination can be used to assess for central nervous system (CNS) involvement, but it is not always necessary for asymptomatic infants 6
- Regular follow-up evaluations can be performed to assess for sequelae and to monitor the infant's development 5, 6
Interpretation of Test Results
When interpreting test results, it is essential to consider the following:
- A reactive FTA-ABS test does not always indicate congenital syphilis, and FTA-ABS reactivity can wane with time 3
- T. pallidum-specific IgM detection alone is inadequate for the diagnosis of congenital syphilis, and a combination of tests may be necessary 4
- The presence of specific IgM should be considered as evidence of a congenital T. pallidum infection, but other tests may also be necessary to confirm the diagnosis 2