Congenital syphilis and perinatal STIs — branching viva

Opening question

Examiner: Take me through this infant. What is the most likely diagnosis, and what is your frame for managing it? [3]

Candidate: The most likely diagnosis is early congenital syphilis. The combination of hepatosplenomegaly, a copper-coloured maculopapular rash on the palms and soles, generalised lymphadenopathy, and snuffles — the profuse blood-tinged nasal discharge teeming with spirochaetes — is classic, and the painful limb suggests osteochondritis with pseudoparalysis of Parrot. The maternal treatment gap, only ten days before delivery when four weeks is needed, confirms high risk. My frame is two-layered: confirm and treat this infant now, and run the public-health response to the maternal, partner and next-pregnancy risk. I would isolate for the infectious secretions, confirm with comparative serology, and start ten days of intravenous aqueous penicillin. [6]

Examiner: Why ten days of intravenous penicillin rather than a single benzathine dose? [6]

Candidate: Because the central nervous system must be penetrated to treat neurosyphilis, and benzathine penicillin does not achieve reliable CSF concentrations. A symptomatic infant — or one with confirmed disease — gets aqueous crystalline penicillin G intravenously for ten days. A single benzathine dose is reserved only for the fully asymptomatic, well-evaluated, low-risk infant whose mother was adequately treated and whose serology is reassuring. [6]

Branch 1 — pathophysiology

Examiner: Explain the pathophysiology. How does the fetus get infected, and why does the maternal stage matter? [1]

Candidate: Treponema pallidum is a spirochaete that circulates in the blood during active disease. A spirochitaemic mother seeds the placenta and fetus haematogenously, with efficient transmission beginning after about sixteen weeks gestation as the placental barrier matures. The risk scales with how active the maternal disease is: primary, secondary and early-latent syphilis carry the highest transmission risk, around 70 to 100 per cent, because they represent active bacteraemia, whereas late-latent and tertiary disease carry a much lower risk. This infant's mother had active disease treated too late. [1]

Examiner: And the mechanism of fetal injury? [3]

Candidate: The spirochaete invades endothelium and perivascular tissue, producing a proliferative endarteritis and obliterative vascular changes that choke the organs forming around those vessels. The liver, with its rich vasculature, bears the brunt — hence the hepatosplenomegaly and jaundice. Bone, actively growing, shows osteochondritis and periostitis. The skin and mucous membranes erupt with the rash and snuffles, and the marrow is suppressed, causing anaemia and thrombocytopenia. When the injury is overwhelming, the fetus develops hydrops and dies in utero. The same vascular mechanism, at a slower tempo, fixes the late stigmata into the still-forming teeth, cornea and cochlea. [3]

Branch 2 — investigations

Examiner: How will you confirm congenital syphilis in this infant? [6]

Candidate: I use two complementary test types. Non-treponemal tests — the RPR or VDRL — measure disease activity and are quantitative; treponemal tests — the TPPA or treponemal immunoassay — confirm past or present infection and stay positive for life. In the infant, I send a quantitative non-treponemal test and compare it with the maternal titre: a neonatal titre fourfold or more higher than maternal strongly suggests true congenital infection rather than passive antibody transfer. I add treponemal IgM, which does not cross the placenta and confirms active neonatal infection, and I complete the workup with a full blood count, liver function tests, CSF cell count protein and VDRL, and long-bone radiographs. Dark-field microscopy or PCR of the nasal discharge can show the spirochaete directly. [6]

Examiner: The treponemal test is positive in the mother but also in her older, well child. What does that mean? [14]

Candidate: That treponemal tests stay positive for life, so a positive treponemal test alone does not distinguish past treated infection from active disease. In the older child, it reflects prior maternal infection or past treatment, and it is the non-treponemal titre trend and the clinical phenotype that matter. This is also why, in the older child with late stigmata, the diagnosis rests on the Hutchinson triad plus the persistent treponemal serology, not on a single titre. [14]

Branch 3 — maternal treatment and the penicillin-allergy question

Examiner: If the mother had reported a penicillin allergy, how would that change her treatment? [13]

Candidate: 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, established by Wendel and colleagues, is to desensitise the woman and treat her with penicillin, the only agent reliably effective against established fetal syphilis. Desensitisation is usually performed in a supervised setting with the penicillin dose given immediately afterward. [13]

Examiner: What reaction should you anticipate after maternal treatment? [13]

Candidate: The Jarisch-Herxheimer reaction — a transient fever, myalgia and uterine activity from spirochaetal antigen release as the organism dies. In pregnancy it can cause transient fetal heart-rate changes and uterine tightenings, so I would monitor the fetus and reassure the woman with antipyretics. It is expected and self-limiting, not an allergic reaction, and it does not require stopping penicillin. The operational rule that completes prevention is that adequate treatment must be finished at least four weeks before delivery. [13]

Branch 4 — the perinatal STIs

Examiner: How do the other perinatal STIs fit into this picture? [6]

Candidate: They are the wider group of infections a mother can pass to her baby around delivery, and they share the prevention frame of screen-and-treat. Neonatal herpes is usually intrapartum, acquired as the baby contacts HSV shed in the genital tract, and presents in the second to third week as SEM, CNS or disseminated disease — any vesicle or unexplained sepsis in that window gets empiric high-dose intravenous acyclovir immediately. Gonococcal ophthalmia neonatorum declares itself at day two to five as a hyperacute purulent conjunctivitis with risk of corneal perforation; it needs systemic ceftriaxone urgently. Chlamydial conjunctivitis comes at day five to fourteen, with a later afebrile staccato-cough pneumonia at two to nineteen weeks treated with oral erythromycin or azithromycin. Vertical HIV and hepatitis B prevention run in parallel. [6]

Examiner: What is the role of routine neonatal ocular prophylaxis? [6]

Candidate: Every newborn should receive ocular prophylaxis within the first hour of life — povidone-iodine, erythromycin or tetracycline — to prevent gonococcal conjunctivitis. Its effect against chlamydia is limited, so chlamydial disease still requires maternal screening and neonatal treatment. Ocular prophylaxis is a cheap, universal prevention layer, but it does not replace antenatal screening of the mother. [6]

Branch 5 — prevention and the resurgent epidemic

Examiner: Congenital syphilis is resurgent in Australia. Why, and what is the prevention strategy? [3]

Candidate: The resurgence is driven by rising syphilis in women of reproductive age, concentrated in Aboriginal and Torres Strait Islander and remote communities, compounded by late or absent antenatal care, inadequate or late treatment, and reinfection. Most cases are missed-prevention failures — no timely test, no timely treatment, or inadequate therapy — which means they are preventable. The prevention strategy is universal antenatal syphilis screening at booking, with repeat testing at twenty-eight to thirty-two weeks and at delivery in high-prevalence settings, immediate stage-appropriate benzathine penicillin treatment completed at least four weeks before delivery, partner treatment, and point-of-care testing and outreach to close the access gap in remote and Indigenous communities. [3]

Examiner: Summarise in one sentence. [6]

Wrap

Candidate: Congenital syphilis is a resurgent, largely preventable spirochaetal infection of the fetus and newborn: recognise the early snuffles phenotype and the late Hutchinson triad, confirm with comparative maternal-and-neonatal serology, treat the mother with benzathine penicillin dosed by stage and the symptomatic infant with ten days of intravenous aqueous penicillin, desensitise the penicillin-allergic pregnant woman, give ceftriaxone for gonococcal conjunctivitis and empiric acyclovir for suspected neonatal herpes, and prevent the case with universal antenatal screening and adequate, timely treatment — because the child who never acquires syphilis is the child the programme has protected. [6] [1]