Syphilis is a sexually transmitted infection caused by the bacterium Treponema pallidum. It has often been called “the great imitator” because so many of the signs and symptoms are indistinguishable from those of other diseases. Accurate testing is critical for diagnosis and treatment.
When is syphilis most infectious?
Syphilis is divided into stages (primary, secondary, latent, and tertiary). A person is most infectious during the primary and secondary stages of syphilis.
The primary stage of syphilis is characterized by the appearance of a single sore or multiple sores at the site of infection. This typically occurs 10-90 days after infection. The sore is often painless and will heal on its own in 3-6 weeks even without treatment. However, the infection remains and can still be transmitted. This stage is highly infectious.
In the secondary stage, a rash appears along with other symptoms like fever, swollen lymph nodes, sore throat, headaches, weight loss, muscle aches, and fatigue. The rash most often appears on the palms of the hands and soles of the feet. This stage usually starts about 4-10 weeks after the syphilis sore appears and can last for up to 6 months. The rash is a sign that the body is reacting to the syphilis bacteria. This stage is also highly infectious.
The latent and late or tertiary stages are periods where symptoms may not be noticeable. However, a person can still transmit syphilis to others during early latent stage. Late latent syphilis is less infectious, but the infection can still be passed. Tertiary syphilis is not infectious.
When is the syphilis antibody test accurate?
There are two main types of blood tests for syphilis screening:
- Nontreponemal antibody tests such as RPR (rapid plasma reagin) and VDRL (Venereal Disease Research Laboratory)
- Treponemal antibody tests such as FTA-ABS (fluorescent treponemal antibody absorption) and TPPA (Treponema pallidum particle agglutination)
Nontreponemal tests check for antibodies that are produced by the body in response to syphilis infection, while treponemal tests look for antibodies that are specific to the bacteria that causes syphilis.
The nontreponemal antibody tests are used for initial screening and can usually detect syphilis within 1-2 weeks of infection. However, false positives are possible. These tests need to be confirmed with a treponemal test.
The treponemal antibody tests are more specific and accurate in detecting syphilis antibodies. These tests confirm a diagnosis when positive but do not distinguish between past and active infection. The FTA-ABS test is considered the gold standard confirmatory test for syphilis.
In summary, nontreponemal tests are ideal for initial syphilis screening but treponemal tests are necessary for accurate diagnosis confirmation.
When is syphilis testing most accurate?
In the early stages of syphilis infection, specifically during the first couple weeks of the primary stage, antibody levels may not be high enough to be reliably detected. Similarly, in late latent syphilis, antibody levels could decline to undetectable levels in some people.
Therefore, syphilis blood tests are most accurate and reliable when performed:
- At least 2-4 weeks after possible exposure to allow sufficient time for antibodies to develop.
- During the secondary stage when antibody levels peak.
If initial screening is negative but recent syphilis exposure is suspected, repeat testing in 2-4 weeks may detect an infection as antibodies rise.
When is syphilis cerebrospinal fluid (CSF) analysis accurate?
Syphilis can sometimes progress to the tertiary stage and affect the brain and central nervous system. This is known as neurosyphilis. Cerebrospinal fluid (CSF) testing can help diagnose neurosyphilis and determine the best treatment approach.
CSF analysis looks for signs of neuroinflammation as well as antibodies produced in response to syphilis infection. Two key tests performed are:
- VDRL: This is the same nontreponemal test as used for blood screening. However, when performed on CSF it is highly specific for neurosyphilis.
- CSF cell count: Elevated white blood cell count, especially increased lymphocytes, indicates inflammation.
CSF-VDRL is positive in only about 30% of neurosyphilis cases, so a negative result does not rule out the diagnosis. The CSF cell count is another useful marker, as a substantially elevated white blood cell count strongly suggests neurosyphilis.
In summary, CSF testing with VDRL and cell count is most accurate and informative when neurosyphilis is suspected based on neurological symptoms or late-stage syphilis infection.
What are the limitations of syphilis testing?
While syphilis blood tests are fairly reliable, there are some limitations to be aware of:
- False positives: Nontreponemal tests like RPR can occasionally be positive when a person does not have syphilis. Confirmatory treponemal testing is important.
- Window period: Testing too early before antibodies have developed or too late when titers are declining can miss infection.
- Past vs active infection: Treponemal tests stay positive for life even after treatment, so do not differentiate current vs past resolved infection.
- Neurosyphilis uncertainty: Negative CSF results do not completely rule out neurosyphilis, if clinical signs are present.
To account for these limitations, syphilis testing may need to be repeated at specific intervals and interpreted in conjunction with a person’s symptoms and risk factors.
What is the syphilis screening schedule?
The CDC recommends the following schedule for syphilis screening for those at risk of infection:
- Initial screening with a nontreponemal test (RPR or VDRL) plus a treponemal test like TPPA.
- Repeat testing at 3 months and 6 months if high-risk exposure occurred to detect new infections, since it may take up to 6 months for antibodies to reach detectable levels.
- Annual screening for those with ongoing high-risk behaviors.
- For pregnant patients, an additional repeat screen at 28-32 weeks gestation and at delivery if at risk.
Persons diagnosed with syphilis should be tested at intervals defined by CDC treatment guidelines to confirm cure after treatment.
Partners of infected patients should be notified, tested, and treated if infected.
Following this screening schedule allows for prompt diagnosis, treatment, and prevention of transmission.
Conclusion
Syphilis testing is most reliable and accurate when performed 2-4 weeks after potential exposure using both treponemal and nontreponemal antibody tests. Repeat testing may be needed to detect evolving antibody titers. CSF testing can confirm neurosyphilis when central nervous symptoms are present. Limitations like false positives and negatives need to be considered. Following the recommended screening schedule in high risk individuals enables early diagnosis and treatment to control spread of infection.