A patient with a genital ulcer and inguinal lymphadenopathy has the following serological results: RPR 1:32 (reactive), TPHA positive. 6 months earlier, RPR was 1:16 with TPHA positive after treatment with 2.4 MU benzathine penicillin IM. Current RPR is now 1:32. What does this represent?

• A Serofast state — TPHA positive with RPR persisting; no treatment needed
• B Biological false positive RPR due to autoimmune disease
• C Prozone phenomenon — false positive at high titre
• D Treatment failure or reinfection — a 4-fold rise in RPR titre (two dilutions) indicates active syphilis requiring re-treatment ✓

Explanation

A 4-fold (two dilution) rise in non-treponemal titre (RPR/VDRL) — in this case 1:16 to 1:64, or 1:8 to 1:32 — indicates treatment failure, inadequate treatment, or re-infection and requires full re-treatment (benzathine penicillin 2.4 MU IM weekly for 3 doses for late/unknown duration, or re-treatment as per stage). RPR titre should fall 4-fold within 6 months of successful primary/secondary syphilis treatment. The serofast state is defined as persistently low and stable (not rising) non-treponemal titres despite adequate treatment, typically seen in late latent syphilis. TPHA remains positive for life after successful treatment and is not used to assess treatment response.

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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