Syphilis Serology
The Rapid Plasmin Reagin (RPR) measures disease activity, but is not specific for syphilis. False RPR positive reactions may occur, notably in patients with connective tissue disorders (false positive reactions are usually low titre < 1:8). For this reason, positive RPR results should be confirmed as due to syphilis by further testing of the serum with a specific treponemal test, e.g.:
- Treponema pallidum haemagglutination (TPHA) assay
- Treponema pallidum particle agglutination (TPPA) assay
- Fluorescent Treponemal Antibody (FTA) assay
- Treponema pallidum ELISA
- Rapid treponemal antibody test
Screening can also be done the other way around starting with a specific treponemal test followed by a RPR in patients who have a positive specific treponemal test. This is sometimes referred to as the “reverse algorithm”.
Once positive, specific treponemal tests generally remain positive for life. The RPR can be used:
- To determine if the patient’s syphilis disease is active or not,
- To measure a successful response to therapy (at least a fourfold reduction in titre, e.g. 1:256 improving to 1:64), or
- To determine a new re-infection
Some patients, even with successful treatment for syphilis, may retain life-long positive RPR results at low titres (≤1:8), which do not change by more than one dilution difference (up or down) over time (so-called serofast patients).
Note:
- Up to 30% of primary syphilis cases, i.e. those with genital ulcers may have a negative RPR.
- The RPR is always positive in the secondary syphilis stage and remains high during the first two (infectious) years of syphilis.
Medicine Treatment
Early Syphilis Treatment
Check if treated at initial visit.
- Benzathine benzylpenicillin, IM, 2 .4 MU immediately as a single dose
- Dissolve benzathine benzylpenicillin, IM, 2 .4 MU in 6 mL lidocaine 1% without epinephrine (adrenaline) .
In penicillin-allergic patients:
- Doxycycline, oral, 100 mg twice daily for 14 days
If penicillin-allergic and pregnant: Refer for penicillin desensitisation.
Late Syphilis Treatment
Check if treatment was commenced at initial visit.
- Benzathine benzylpenicillin, IM, 2 .4 MU once weekly for 3 weeks .
- Dissolve benzathine benzylpenicillin, IM, 2 .4 MU in 6 mL lidocaine 1% without epinephrine (adrenaline).
If penicillin-allergic and pregnant: Refer for penicillin desensitisation.
Syphilis in Pregnancy
Mother-to-child transmission of syphilis occurs in up to 40% of cases in untreated mothers. Untreated maternal syphilis may lead to miscarriage, stillbirth, non-immune hydrops fetalis, or congenital syphilis in the newborn. Syphilis may be asymptomatic in pregnant women with diagnosis made by positive serology, preferably with on-site rapid testing.
Referral
- Neurosyphilis
- Clinical congenital syphilis
