In 2014,19,999 cases of syphilis were reported in the United States (double the amount seen in 2000). It seems as if clinicians and students alike are confused as to how to properly screen for this disease.
High risk: men who have sex with men (MSM), HIV, incarceration, and commercial sex work. MSM and those with HIV who are screened every 3 months are more likely to be diagnosed at various stages of disease when compared to once annual screening.
Half of MSM who have HIV are also co-infected with syphilis and men under 29 years of age are 3 times more likely to be infected with the disease. Syphilis rates were 18.9 cases per 100,000 in blacks vs 3.5 per 100,000 in whites.
Screening the asymptomatic patient:
It’s a 2-step process involving an initial nontreponemal test (VDRL or RPR] test) followed by a confirmatory treponemal antibody detection test (fluorescent treponemal antibody absorption [FTA-ABS] or Treponema pallidum particle agglutination [TP-PA] test).
The nontreponemal tests are sensitive but not specific. Many reasons as to why they can be falsely positive. So, if positive confirm with treponemal antibody test – if this is negative no further workup is required unless there is high suspicion because initial testing may be negative early in the disease (repeat in 2-4 weeks). 1-2% of the population will have false positives – especially true in pregnancy.
A reverse order of testing has been described by the CDC where you start with the treponemal antibody testing and confirm with the nontreponemal test. It’s positive and negative predictive value isn’t all too clear.
If both are positive then this is consistent with infection. The next step is to ask about prior infection and to look at the nontreponemal titer. If the titer is low and the patient has been treated no further management is necessary. If the patient was never treated and the titer is high – then treatment is necessary.
Titers decline with treated infection (may or may not remain positive for life) and will also wane with very old untreated infection. Treponemal anitbody tests will remain positive for life.
Titers are considered low if less than 1:8. Patients are considered serofast if titers remain at 1:8. New syphilis infection is diagnosed when titers increase 4x from their baseline after previous treatment.
If the reverse testing is done and we have a positive antibody test but negative RPR/VDRL then this indicates successfully treated syphilis. If there is no history of treatment then look for signs
of early syphilis as this may indicate the RPR/VDRL is falsely negative because it was done too soon.
If signs and symptoms (chancre and rash) are found – repeat a second nontreponemal test and treat. If no signs are found perform a second antibody test for the possible diagnosis of late latent syphilis (RPR/VDRL can become negative with very old infection).
If positive – treat. If negative – this is considered a false positive (spirochetal infections, malaria, and leprosy) and no further syphilis workup required.