Congenital syphilis and perinatal sexually transmitted infections — formative SAQs

SAQ 1 (10 marks)

A two-week-old infant from a remote northern Australian community is brought in with poor feeding, fever, and a swollen abdomen. On examination there is hepatosplenomegaly, a copper-coloured maculopapular rash on the palms and soles, generalised lymphadenopathy, and a profuse blood-tinged nasal discharge. The left arm is held still and appears tender. The mother booked late to antenatal care; her syphilis serology was treated with a single dose of benzathine penicillin only ten days before an uncomplicated vaginal delivery. [3]

Question: Outline the diagnosis, investigations, immediate and stepwise management of this infant, including the maternal-treatment-adequacy review and public-health follow-up. (10 marks) [6]

Model answer

Diagnosis and disposition (2 marks). This is classic early congenital syphilis: hepatosplenomegaly, the copper maculopapular rash on palms and soles, generalised lymphadenopathy, snuffles (the profuse blood-tinged nasal discharge teeming with spirochaetes), and the painful osteochondritis causing pseudoparalysis of Parrot in the left arm. The maternal treatment gap (only ten days before delivery, far less than the four weeks needed for prevention) confirms high risk. Admit for full evaluation, empiric therapy, and isolation for the infectious secretions. [6]

Investigations (3 marks). Send comparative serology: a quantitative non-treponemal test (RPR) on the infant compared with the maternal titre — a neonatal titre fourfold or more higher than maternal strongly suggests true congenital infection — plus treponemal IgM (19S-IgM), which does not cross the placenta and confirms active neonatal infection. Add a full blood count and film (anaemia, thrombocytopenia), liver function tests, a lumbar puncture for CSF cell count, protein and CSF VDRL, and long-bone radiographs for the osteochondritis and periostitis. Dark-field microscopy or PCR of the nasal discharge can demonstrate spirochaetes directly. Confirm the maternal serology and treatment record. [6] [3]

Treatment (3 marks). Treat with aqueous crystalline penicillin G intravenously for ten days, because the CNS must be penetrated and benzathine penicillin does not achieve reliable CSF concentrations. Provide supportive care — fluids, transfusion for severe anaemia, antipyretics — and treat intercurrent problems. Isolate for the infectious secretions with standard precautions and gloves. Do not use a single benzathine dose for a symptomatic infant. [6]

Maternal-treatment review and public health (2 marks). Review the maternal treatment adequacy: a single benzathine dose ten days before delivery is inadequate by timing — the four-week-before-delivery rule was not met — placing the infant at high risk. Notify public health, trigger partner notification and treatment, and arrange maternal and partner sexual-health follow-up. Plan long-term infant surveillance: quantitative non-treponemal serology every two to three months until non-reactive, plus developmental, audiological and ophthalmological surveillance for the late stigmata (Hutchinson teeth, interstitial keratitis, eighth-nerve deafness). Address the access barriers (remoteness, late booking) that drove the missed prevention. [11] [14]

SAQ 2 (10 marks)

Question: A 26-year-old woman at 30 weeks gestation is found on routine antenatal screening to have a reactive RPR at 1:32 with a confirmed positive TPPA. She has no symptoms. She reports a penicillin allergy (urticaria after amoxicillin). (a) What is the diagnosis, staging, and the correct maternal treatment regimen? (b) How will you manage her penicillin allergy, and what reaction should you anticipate after treatment? (c) What is the operational prevention rule governing treatment timing, and what is the neonatal plan at delivery? (10 marks) [6]

Model answer

(a) Diagnosis, staging and treatment (3 marks). The diagnosis is latent syphilis in pregnancy confirmed by a reactive non-treponemal test (RPR 1:32) and a positive treponemal test (TPPA), with no clinical features of primary or secondary disease. The staging determines the regimen: early-latent disease (acquired within one year) is treated with a single intramuscular dose of benzathine penicillin G; late-latent or unknown-duration disease requires three doses one week apart. Benzathine penicillin is the only regimen proven to prevent congenital infection effectively. Do not substitute an alternative antibiotic in pregnancy. [6] [11]

(b) Penicillin allergy and the anticipated reaction (3 marks). Penicillin allergy in pregnancy with active syphilis is a desensitisation problem, not a substitution problem. Erythromycin, azithromycin and the tetracyclines do not reliably cross the placenta and do not cure fetal infection; ceftriaxone has limited evidence in pregnancy. The proven approach (Wendel et al.) is to desensitise the woman and treat her with penicillin, the only agent reliably effective against established fetal syphilis. After treatment, anticipate the Jarisch-Herxheimer reaction — a transient fever, myalgia and uterine activity from spirochaetal antigen release — which is expected and self-limiting; monitor the fetus and reassure the woman with antipyretics. [13]

(c) Prevention timing and neonatal plan (4 marks). The operational rule is that adequate maternal treatment must be completed at least four weeks before delivery to prevent congenital infection, so a woman first treated at 30 weeks has time to complete the regimen and show a titre response before labour. After treatment, monitor the non-treponemal titre for a fourfold fall over the following months, treat the partner, and re-screen for reinfection if ongoing risk. At delivery, risk-stratify the newborn by maternal treatment adequacy and titre trend: because she was adequately treated more than four weeks before delivery with a falling titre, the infant is lower risk and may need careful examination, comparative serology and follow-up rather than empiric ten-day therapy — but any sign of clinical disease, a rising titre, or treatment within four weeks of delivery escalates the infant to full evaluation and treatment. [6] [11]