Background: Identification of infants with Treponema pallidum infection of the central nervous system remains challenging.
Methods: We used rabbit-infectivity testing of the cerebrospinal fluid to detect T. pallidum infection of the central nervous system in infants born to mothers with syphilis. The results were compared with those of clinical, radiographic, and conventional laboratory evaluations; IgM immunoblotting of serum and cerebrospinal fluid; polymerase-chain-reaction (PCR) assay testing of serum or blood and cerebrospinal fluid; and rabbit-infectivity testing of serum or blood.
Results: Spirochetes were detected in the cerebrospinal fluid of 19 of 148 infants by rabbit-infectivity testing. Exposure of the infant to antibiotics before cerebrospinal fluid was obtained for rabbit-infectivity testing was associated with a negative test result (P=0.001). Spirochetes were detected in the cerebrospinal fluid in 17 of 76 infants (22 percent) who had no prior antibiotic exposure. These 17 infants included 41 percent (16 of 39) of those with some abnormality on clinical, laboratory, or radiographic evaluation; 60 percent (15 of 25) of those with abnormal findings on physical examination that were consistent with congenital syphilis; and 41 percent (17 of 41) of those with a positive result on IgM immunoblotting or PCR testing of serum, blood, or cerebrospinal fluid, or a positive result on rabbit-infectivity testing of serum or blood. Only one infant who had normal findings on clinical evaluation had a positive cerebrospinal fluid rabbit-infectivity test. Overall, central nervous system infection was best predicted by IgM immunoblotting of serum or PCR assay of serum or blood.
Conclusions: Most infants with T. pallidum infection of the central nervous system can be identified by physical examination, conventional laboratory tests, and radiographic studies. However, the identification of all such infants requires the use of additional tests, including IgM immunoblotting and PCR assay.