Syphilis is a sexually transmitted infection caused by the bacterium Treponema pallidum. While syphilis can be tricky to diagnose in some cases, there are some key signs and tests that doctors use to identify syphilis.
How is syphilis transmitted?
Syphilis is primarily spread through sexual contact with an infected person. The bacteria typically enter the body through mucous membranes such as the mouth, vagina, penis, or anus. Less commonly, syphilis can be spread through contact with open sores during the secondary stage of infection. Syphilis can also be transmitted from mother to baby during pregnancy or childbirth.
What are the stages of syphilis?
Syphilis progresses through four different stages if left untreated:
- Primary syphilis – Characterized by a painless sore called a chancre at the site of infection. The chancre develops around 3 weeks after exposure and will heal on its own after 3-6 weeks.
- Secondary syphilis – Usually occurs 2-8 weeks after the chancre heals. Symptoms include a rash on the palms, soles of feet, mouth, genitals or other parts of the body. Other symptoms may include fever, swollen lymph nodes, sore throat, patchy hair loss, headaches, weight loss, muscle aches, and fatigue.
- Latent syphilis – After secondary syphilis, the infection enters a latent phase where there are no symptoms. Latent syphilis is divided into early latent (less than 1 year after infection) and late latent (more than 1 year after infection).
- Tertiary syphilis – The final stage of syphilis that occurs 10-30 years after infection. Symptoms include difficulty coordinating muscle movements, paralysis, numbness, gradual blindness, and dementia. Major organ systems can be damaged leading to heart disorders, neurological problems, and even death.
How is syphilis diagnosed?
Diagnosing syphilis requires a combination of physical examination, medical history, and lab tests. Here are some of the main ways syphilis is diagnosed:
Physical exam
A provider will perform a physical exam looking for signs of syphilis such as rashes, sores or lesions on the genitals, mouth, hands or other body parts. Enlarged lymph nodes may also be felt during palpitation.
Medical history
Information about symptoms, sexual history, and possible exposures can help determine risk of syphilis infection. Providers will ask about any sores or rashes noticed, as well as ask about high-risk sexual behaviors.
Microscopic examination
During primary or secondary syphilis, fluid from a chancre or syphilis sore may be examined under a microscope. This allows providers to visually confirm the presence of Treponema pallidum bacteria.
Blood tests
There are two main types of blood tests used to diagnose syphilis:
- Nontreponemal tests – Also called RPR or VDRL tests, these look for antibodies produced by the body in response to syphilis infection. A positive test means antibodies were detected but doesn’t definitively diagnose syphilis.
- Treponemal tests – Tests for specific antibodies to Treponema pallidum. Includes tests like FTA-ABS, TP-PA, enzyme immunoassays, and chemiluminescence immunoassays. Positive results strongly indicate syphilis infection.
Often nontreponemal tests are used for initial screening, followed by a treponemal test to confirm diagnosis. Two types of blood tests are recommended due to the possibility of false positive or false negative results from just one test.
Cerebrospinal fluid analysis
In later stage syphilis, a sample of cerebrospinal fluid may be analyzed for evidence of syphilis infection in the central nervous system. Abnormalities may indicate neurosyphilis.
How soon can syphilis be detected?
The time from syphilis infection to detection depends on the stage of the disease:
| Stage | Time from Infection | Time to Detection |
|---|---|---|
| Primary syphilis | 3 weeks | Can often be detected during initial chancre |
| Secondary syphilis | 3-6 weeks | Symptoms prompt testing which can confirm diagnosis |
| Latent syphilis | After secondary stage | Patient has no symptoms, requires screening |
| Tertiary syphilis | 10-30 years | Symptoms bring patient in for testing |
During the primary and secondary stages, symptoms are apparent prompting earlier testing and detection. Latent syphilis with no symptoms can only be detected through screening high risk individuals. Tertiary syphilis occurs decades later when antibody levels may decrease and symptoms warrant testing.
Who should be tested for syphilis?
The CDC recommends routine syphilis screening for the following populations:
- Pregnant women at first prenatal visit with additional screening later in pregnancy for high risk women
- People with HIV infection should have syphilis testing at time of HIV diagnosis and annually after that
- Men who have sex with men should have annual syphilis screening
- Screening 3 months after diagnosis with other STIs such as gonorrhea or chlamydia
- Individuals who exchange sex for drugs or money
- Testing when people present with signs/symptoms of primary or secondary syphilis
In areas with high syphilis prevalence, screening high-risk groups more frequently than yearly may be useful. Treating partners of infected individuals is also essential. Universal screening is not recommended for low-risk heterosexuals.
Why can syphilis be hard to diagnose?
There are a few reasons properly diagnosing syphilis can be challenging at times:
Nonspecific symptoms
The signs of secondary syphilis like rash, fever, sore throat and fatigue are fairly general. The rash may be dismissed as a mild viral infection. Unless healthcare providers test specifically for syphilis, it can be mistaken for other diseases.
Overlapping stages
The stages of syphilis may overlap, with symptoms of the secondary stage occurring while the chancre is still present. This can muddy the clinical picture and make it less straightforward to diagnose.
Asymptomatic phases
During latent syphilis, infected individuals have no symptoms at all. Unless high risk groups are screened, latent syphilis goes undiagnosed.
Unreliable antibody response
Some patients may not produce the expected antibodies, leading to negative test results even when syphilis is present. Weakened immune systems can alter antibody production.
Treatment masking disease progression
If patients are treated with antibiotics that resolve some initial symptoms without fully curing the infection, they may not progress to later stages. Lack of symptom progression makes it difficult to reach a syphilis diagnosis.
Conclusion
While syphilis diagnosis can be complex, doctors have a reliable set of tests to detect most cases. Screening high-risk individuals and recognizing symptom patterns are key. Public health efforts to increase awareness and testing have improved early detection. Advances in laboratory tests also support accurate diagnosis. Although syphilis prevalence is rising in the U.S., improved clinical practices are combating this trend with better detection and treatment.