Infection: Syphilis; Treponema pallidum infection; many other historical names

Brief description:
  • A sexually transmitted bacterial infection.
  • Typically begins as a painless ulcer (primary syphilis) at point of inoculation (i.e. usually on genitals, but can be e.g. oral if acquired via oral sex). Often goes unnoticed. If untreated can then disseminate (secondary syphilis), most commonly seen as a generalised rash. May then over a longer period cause tertiary syphilis e.g. chronic neurologic, vascular disease.
  • Highest, and increasing, incidence seen in men who have sex with men (MSM), however increasing in women also. Can cause serious congenital infection.
Did you know?

Syphilis can present in many different ways: it has been known as ‘the great mimicker’.

Who should I test?
  • Due to increasing incidence, the fact presentations can be highly variable, and testing is straightforward, the threshold for testing should be low.
  • Any undiagnosed genital ulcer in a sexually active person should prompt testing.
  • MSM: test at least annually, and with any unexplained systemic or genital symptoms.
Test of choice:

Request Syphilis serology

Can answer two questions:

  • Has this person ever had infection with syphilis (including if treated/cleared)?
    • EIA and TPPA
  • Does this person have current active infection?
    • RPR

Syphilis EIA detects anti-treponemal antibodies (a ‘treponemal’ test). These develop shortly after primary infection and usually last lifelong i.e. indicate infection at some stage.

  • Excellent sensitivity – a negative result excludes syphilis unless very early infection/treatment, or rarely in HIV/immune compromise
  • Good specificity – however, a second test is used to confirm a positive result, as false positives can occur.
    • TPPA (another ‘treponemal’ test) is used for this purpose
      • EIA pos &TPPA pos = treponemal infection at some stage. Note, other treponemal infections, e.g. Yaws, give the same result.
      • EIA pos &TPPA neg = false positive EIA (most common explanation) or very early infection.

RPR detects non-specific antibodies (a ‘non-treponemal’ test) caused by active infection.

  • This is added on automatically by the lab in patients with a positive EIA and TPPA.
  • Unlike EIA/TPPA, which remain positive regardless, the value of this test changes over time due to treatment or the immune response to infection.
  • Used to assess for inactive vs active infection and response to treatment.
Tests to avoid/specialist tests:

Syphilis PCR of a lesion

  • Rarely offers additional information over serology. Reserved for specialist use.
Other considerations:

Is notifiable and requires contact tracing. Sexual Health should be involved in the management of people with suspected or proven syphilis.