Article in Japanese

A case of congenital syphilis diagnosed by serologic retesting

Kensuke Horinouchi^1）, Yuichi Kodama^1）, Daisuke Hazeki^1）, Ryo Kusubae^1）, Yuichi Nomura^1）, Toshiro Fukushige^1）

Diagnosing congenital syphilis is challenging in neonates born to mothers with negative syphilis serology during early pregnancy. This study reports a case of congenital syphilis diagnosed by serologic retesting. A male infant was delivered by cesarean section at 39 weeks and 4 days of gestation, weighing 2,770 g. The mother’s syphilis serology was negative at 13 weeks of gestation. At 27 weeks, she developed genital herpes, which improved with oral treatment. The infant was discharged on day 6 of life without complications. On day 21, he was admitted with fever and poor feeding. Physical examination revealed erythematous papules and hepatomegaly. Laboratory tests showed a white blood count （WBC） of 9,900/μL, C-reactive protein （CRP） of 8.0 mg/dL, and platelet count of 70,000/μL. Empirical treatment with ampicillin, cefotaxime, and acyclovir was started. Initial Treponema pallidum hemagglutination assay （TPHA） was 14.7 COI and rapid plasma reagin （RPR） was ＜0.3 R.U. The fever resolved by day 2, but on day 8, the mother developed a faint rash and tested positive for TPHA and RPR. Repeat testing in the infant showed increased TPHA （182 COI） and RPR （1.8 R.U）. Considering the clinical findings and serologic results, the diagnosis of congenital syphilis was made, and the infant was treated with intravenous benzylpenicillin for 10 days. This case highlights the importance of repeated serologic testing in infants suspected of congenital syphilis, even when initial test results are negative.

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1）Department of Pediatrics, Kagoshima city Hospital

Key words	congenital syphilis, neonatal infection, serologic testing
Received	September 29, 2025
Accepted	February 1, 2026

38 (1)：19─25,2026