Syphilis Screening in Pregnant Women

Syphilis is caused by the spirochete bacterium, Treponema pallidum.  In the primary stage of disease patients may present with a sore or chancre typically located at the site of infection.  During the secondary stage patients may show symptoms of rash, fever and general malaise.  And in the late or latent stages, there may be organ damage, paralysis or mental status changes.

In a recent article in the Clinical Review and Education section of JAMA, it examined the recommendation of the US Preventive Services Task Force (USPS) reaffirming continued screening for syphilis in pregnant women.  The article also examined the current laboratory methodologies for syphilis screening.

Serological testing has been the commonly used diagnostic tool for many decades.  There are two types of serologic tests.  Non-treponemal assays have endured the test of time and they detect antibodies to nonspecific antigens such as cardiolipin that are produced in most patients with syphilis infection.  Examples of non-treponemal tests include rapid plasma regain (RPR) and the venereal disease research laboratory (VDRL) assays.  These tests have low sensitivity in very early or late disease and, in addition, they generally become negative after treatment.  They also have a low sensitivity in areas where the prevalence of syphilis is low and false positive results are not uncommon in low prevalence settings. 

The second serologic tools are the treponemal assays which detect antibodies against specific T. pallidum antigens.  Examples of such tests are the Treponema pallidum particle agglutination test (TP-PA) and the fluorescent treponemal antibody (FTA) test.  There are multiple ELISA direct assays which are widely used. These treponemal assays remain positive for years after treatment. 

The choice of first line test today is the treponemal test.  When a treponemal screening test has negative results, no further testing is needed unless early syphilis is suspected.  However, if the results are positive, follow up with a non-treponemal test is indicated.  If the non-treponemal result is negative a second treponemal assay should be performed to assist in result interpretation.

Coming back to the USPS recommendation to continue to screen pregnant patients for syphilis, remember untreated maternal syphilis infections can lead to congenital syphilis which is associated with stillbirth, neonatal death, bone deformities and neurologic impairment.  It is recommended that all pregnant women be tested for syphilis when they first present.  CDC and ACOG also recommend repeat screening in the third trimester in women at high risk for acquiring syphilis and again at the time of delivery.  High risk is generally defined as living in communities with high syphilis prevalence, patients infected with HIV and those with a history of incarceration or commercial sex work.