Seroreversion of serological tests for syphilis in neonates born to mothers with syphilis: a follow-up study

Abstract

Objective To observe the seroreversion of serological tests for syphilis in neonates born to mothers with syphilis and to evaluate the influence of antisyphilitic treatment on the time of seroreversion in uninfected neonates.Methods A total of 115 neonates born to mothers with syphilis were recruited in this study,and underwent toluidine red unheated serum test (TRUST),Treponema pallidum particle assay (TPPA)and 19S IgM-TPPA at birth.Follow up was scheduled at 1,3,6,9,12,18 and 24 months of age,and cancelled as soon as both TRUST and TPPA became negative during the 24 months.Both TRUST and TPPA were carried out at each follow-up visit.Kaplan-Meiter survival analysis and Wilcoxon rank-sum test were conducted to assess these data by using SPSS 13.0 software.Results At birth,TPPA was positive in all (100％) of the neonates,TRUST in 97 neonates (84.3％) with the titer ranging from 1 ∶ 1 to 1 ∶ 256,19S IgM-TPPA in 3 neonates who were diagnosed with congenital syphilis (CS).CS was ruled out in the other 112 neonates with negative 19S IgM-TPPA after follow up.Of the 3 neonates with CS,all became negative for TRUST within 12-18 months after birth,2 remained positive for TPPA at 24 months of age,1 remained positive for TPPA at 20 months of age,and all were still followed at the time of this writing.The cumulative seroreversion rate was 82.2％,98.9％ and 100％for TRUST at 0-3,4-6 and 7-9 months of age,respectively in 90 uninfected neonates,3.1％,30.2％,85.4％ and 100％ for TPPA at 0-3,4-6,7-9 and 10-12 months of age,respectively in 96 uninfected neonates.Of 16 neonates who missed some follow-up visits,all turned negative for TRUST and TPPA within 15 months after birth.As far as the TP-seropositive uninfected neonates were concerned,no statistical differences were observed in the seroreversion time of TRUST or TPPA between neonates receiving antisyphilitic treatment and those without antisyphilitic treatment (x2 =0.54,2.41,respectively,both P ＞ 0.05).The seroreversion of TRUST occurred earlier than that of TPPA (Z =10.45,P ＜ 0.01).Conclusions Most uninfected neonates born to syphilitic mothers turn negative for TRUST within 6 months after birth,and for TPPA within 12 months.And the seroreversion of TRUST usually occurs earlier than that of TPPA.Antisyphilitic treatment shows no significant influence on the seroreversion time of TRUST or TPPA in these seropositive uninfected infants. Key words: Syphilis; Syphilis, congenital; Syphilis serodiagnosis; Follow-up studies