Syphilis at 26 weeks' gestation with a history of penicillin anaphylaxis
A 27-year-old woman attends the antenatal clinic at 26 weeks' gestation. Booking serology shows RPR 1:16 and a positive TPPA; HIV and hepatitis B are negative. She mentions that about four months ago she had a painless ulcer on the labia that healed without treatment. She has no rash now. Three years ago she was treated for syphilis - she recalls 'two injections a week apart' - and her notes record a fall in RPR to 1:2. She reports anaphylaxis to penicillin as a child: urticaria, lip swelling and wheeze after amoxicillin. She lives with a partner of two years and asks you not to tell him anything. She is otherwise well and takes no regular medication.
1. How do you stage the infection, and what serological pattern would have changed your interpretation?
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Stage: early syphilis - most likely early latent with a recent reinfection, or secondary syphilis with the chancre being the primary lesion.
Reasoning:
- A painless genital ulcer four months ago is a chancre until proven otherwise, which places acquisition within the last 12 months - i.e. early syphilis, whether or not a rash is present.
- She has been treated before and her RPR fell to 1:2, which is a documented serological response. A rise to 1:16 with a new chancre is therefore much more likely to be reinfection than treatment failure three years later.
- TPPA stays positive for life, so it confirms the diagnosis but says nothing about activity; RPR is the activity marker here.
What would change my interpretation:
- A stable RPR of 1:2 with no chancre would have been a serofast result, not reinfection.
- An RPR that had never fallen after the earlier treatment would have raised treatment failure or late latent disease, in which case she would need three weekly doses rather than one.
- If the ulcer had been present more than 12 months ago, or if she could not date any lesion, I would treat as syphilis of unknown duration (three weekly doses) - the safe default in pregnancy.
Because duration is genuinely uncertain in the mind of a patient recalling a childhood injection schedule, I would state the stage clearly in the notes and justify why I chose early rather than unknown duration.
2. Write the treatment you would give today, dealing with the penicillin allergy, and explain the monitoring you would arrange.
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Treatment: benzathine benzylpenicillin 2.4 million units IM, given after formal desensitisation.
Why not just use an alternative?
- Penicillin is the only regimen proven to treat the fetus as well as the mother and to prevent congenital syphilis. There is no equally effective substitute.
- Doxycycline is contraindicated in pregnancy (tetracycline bone and tooth effects).
- Macrolides (erythromycin, azithromycin) cross the placenta unreliably, do not reliably cure fetal infection, and macrolide resistance in Treponema pallidum is well described. Using them would look like treatment while leaving the baby at risk.
Practicalities:
- Admit for oral or intravenous penicillin desensitisation according to a validated protocol, with resuscitation facilities available; her childhood reaction (urticaria, angioedema, wheeze) is a genuine immediate-type history and must not be dismissed.
- After desensitisation, give the full dose and keep her under observation. Continue penicillin cover if further doses are needed (a second dose one week later is used by many services in pregnancy, and three weekly doses are required if duration is uncertain).
- Warn her about the Jarisch–Herxheimer reaction - fever, myalgia, rigors, and in pregnancy possibly contractions or transient fetal distress. Give fetal monitoring if the unit's practice is to do so at this gestation, and ensure she knows to attend if she has reduced fetal movements.
- Repeat RPR at 28 weeks and at delivery, then at 3, 6 and 12 months; a fourfold fall is the expected response. Retest for HIV in the third trimester.
- Arrange neonatal assessment regardless of maternal response: examination, neonatal (not cord) serology, and investigation or empirical treatment if there are any abnormal findings.
3. She asks you not to tell her partner anything. How do you handle partner notification, confidentiality and the risk to the fetus?
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Confidentiality is the starting point, but this is not a 'say nothing' situation.
- I would not contact the partner without her consent. Sexual health confidentiality is a core professional obligation and breaching it without justification would destroy the trust needed to keep her in care - and she needs to complete treatment and follow-up for the sake of the pregnancy.
- I would explain, plainly, that her partner has almost certainly been exposed and that treating him prevents reinfection of her and infection of the baby. Reframing partner notification as something done for her and the pregnancy is more effective than a public-health lecture.
- I would offer the full menu: patient referral with written information, provider referral (I contact him without naming her if that is locally permissible), or a hybrid where she tells him and I confirm the appointment.
- I would explore why she does not want him told - fear of violence, relationship breakdown, or infidelity concerns are common, and any disclosed risk of domestic abuse triggers a safeguarding conversation and safety planning, not just a lecture on epidemiology.
- I would document the discussion, her decision, the risk explained, and the offer of help. If she continued to refuse and there were a serious risk to an identifiable third party, most jurisdictions permit disclosure in the public interest; that decision belongs at consultant/caldicott-guardian level, not as an impulsive act in clinic.
- Separately, the fetus is a patient too: I would ensure the neonatology team is informed, that she understands congenital syphilis is preventable but not curable once established, and that her follow-up is booked before she leaves.