What type of syphilis does a 23‑week pregnant woman with a history of reactive rapid plasma reagin six years ago, a low non‑treponemal titer, and a positive treponemal test have?

Classification: Late Latent Syphilis (Previously Treated)

This pregnant patient has late latent syphilis with a history of prior treatment, evidenced by her reactive treponemal antibody (which remains positive for life), low RPR titer of 1:2, and documented reactive RPR six years ago. 1

Staging Rationale

• Late latent syphilis is defined as infection acquired more than 12 months previously, which clearly applies to this patient with a 6-year history of reactive serology. 1, 2

• The low RPR titer (1:2) is entirely consistent with late-stage disease, as nontreponemal antibody titers naturally decline over time following infection or treatment, with only 41% of late latent cases maintaining titers >1:8. 2

• Treponemal antibodies (positive in this patient) remain reactive for life in 75-85% of patients regardless of treatment status, so this result alone cannot distinguish active from previously treated infection. 3

Critical Determination: Adequately Treated vs. Untreated

The single most important clinical question is whether she received appropriate penicillin treatment after that reactive RPR 6 years ago:

If She Was Adequately Treated 6 Years Ago:

• No additional treatment is required if she received benzathine penicillin G (either 2.4 million units IM × 1 dose for early syphilis OR 2.4 million units IM weekly × 3 weeks for late latent) more than 4 weeks before this pregnancy, her RPR titer declined appropriately (≥4-fold), and there is no evidence of reinfection. 1, 4

• The current RPR of 1:2 represents a "serofast" state—persistent low-level reactivity that does not indicate treatment failure or active disease. 3, 2

• Reinfection should be suspected only if there is a 4-fold rise in titer above her established baseline (e.g., if her post-treatment titer was 1:1 and is now 1:4, or if it was nonreactive and is now 1:2). 3

If Treatment History Is Unknown or Inadequate:

• She must be treated immediately as late latent syphilis with benzathine penicillin G 2.4 million units IM once weekly for 3 consecutive weeks (total 7.2 million units). 1, 2

• Penicillin is the only acceptable treatment during pregnancy to prevent congenital syphilis; if she reports penicillin allergy, she must undergo desensitization. 1, 4

• Treatment must be completed at least 4 weeks before delivery to be considered adequate for preventing congenital infection. 1, 4

Mandatory Concurrent Actions

• Review all prenatal and historical medical records to document: (1) whether she received penicillin treatment after the positive test 6 years ago, (2) what her RPR titers were at that time and subsequently, and (3) whether titers declined ≥4-fold after treatment. 4

• HIV testing is essential immediately if not already performed this pregnancy, as HIV coinfection significantly increases neurosyphilis risk and alters monitoring requirements. 4, 3, 2

• Assess for any neurologic or ocular symptoms (headache, vision changes, cranial nerve dysfunction) that would mandate CSF examination to exclude neurosyphilis. 1, 4

Infant Management

• If the mother was untreated or inadequately treated (treatment <4 weeks before delivery, wrong antibiotic, or no documented 4-fold titer decline), the infant requires full evaluation including CSF examination, long-bone radiographs, CBC with platelets, and treatment with aqueous crystalline penicillin G 100,000-150,000 units/kg/day IV for 10 days. 1, 4

• If the mother received adequate treatment >4 weeks before delivery with documented serologic response, the infant may require only a single dose of benzathine penicillin G 50,000 units/kg IM or close serologic follow-up without treatment. 1, 4

Follow-Up Monitoring

• Quantitative RPR titers should be checked at 6,12, and 24 months after any new treatment using the same test method and laboratory. 3, 2

• Infant nontreponemal titers should be monitored at 3,6,12, and 15 months of age; passively transferred maternal antibodies should decline and become nonreactive by 6 months. 4

Critical Pitfalls to Avoid

• Never use the treponemal test result to monitor disease activity or treatment response—it remains positive for life regardless of cure. 4, 3

• Do not assume low titers mean no treatment is needed—if her treatment history is uncertain, she requires the full 3-week late latent regimen regardless of the 1:2 titer. 2

• Do not delay treatment waiting for old records—if documentation cannot be obtained promptly, treat empirically as untreated late latent syphilis to protect the fetus. 4

• Do not use alternative antibiotics (doxycycline, azithromycin, ceftriaxone) during pregnancy—only penicillin prevents congenital syphilis. 1, 4