Blog Series Part 1: Key Periods for Diagnosing Syphilis


Intended Audience:

  1. Healthcare professionals looking for a syphilis public education resource
  2. Community educators looking for a syphilis community education resource
  3. People who are sexually active with multiple partners who want to learn more about syphilis
  4. People in general who want to learn more about syphilis


In the first blog of the series, we will define and illustrate some common terms related to key periods for diagnosing syphilis. It is commonly known that syphilis is a sexually transmitted infection (STI) and can be treated and cured with antibiotics. Worth mentioning, however, is that diagnosing syphilis can sometimes be challenging which can then create a second challenge for timely treatment. There are a variety of reasons behind the challenge of diagnosis that include:


  • Asymptomatic cases: Not all individuals with syphilis exhibit symptoms, especially in the early stages. Asymptomatic cases can lead to delays in seeking testing and diagnosis.
  • Variability in Symptoms: The symptoms of syphilis can be varied and may mimic those of other infections. This variability can make clinical diagnosis challenging.
  • Different Stages of Infection: Syphilis has distinct stages, and the accuracy of tests can vary depending on the stage. Tests that are reliable in one stage may not perform as well in another.
  • Diagnostic Tests: While blood tests are commonly used, if a person has a visible sore (chancre), a swab of the sore can also be tested. However, this method may not be as sensitive as blood tests. Furthermore, both the swab and blood test method have respective periods of time in the progression of syphilis where they can better detect antibodies.

A piece of knowledge that assists healthcare professionals in diagnosing syphilis is knowing about the incubation period, stages of symptoms, window period, and testing window. The same knowledge can be useful for sexually active individuals to understand the timing of getting tested based on potential exposure or onset of symptoms.


Defining the Incubation Period, Stages of Symptoms, Window Period, and Testing

FIGURE 1 below shows that after a person is exposed to a syphilis infection, the bacteria grow inside the body (incubation period) which can lead to acquiring a syphilis infection indicated by symptoms in the primary, then secondary stage of syphilis. When left untreated, symptoms can enter a hidden period called latency, or the latent stage. However, the person remains infected. Furthermore, a tertiary stage of syphilis can emerge years later after the latency which can be life threatening if still left untreated.


FIGURE 2 below shows that after a person is exposed to a syphilis infection, the bacteria are growing in the body and producing antibodies. However, there is a period when although antibodies are building up, there are not enough of them to be detected by a syphilis blood test for diagnosis which is called the window period. When enough antibodies are present in the body to be accurately detected by a diagnostic blood test it’s called the testing window.



Figures 1 and 2 might be helpful in providing some general definition, but they do not indicate any measurement of time. A key factor that can complicate the diagnosis of syphilis, is that the incubation period for any given individual may vary from days to weeks. For example, one person might experience a short incubation period and another person a long incubation period. Since the incubation and window periods can fluctuate, this affects the timing of showing symptoms and subsequently the timing of both transmissibility and the testing window.

Understanding the incubation period, stages of symptoms, window period, and testing window of syphilis can be beneficial because…



FIGURE 3 below shows measures of time applied to the various periods that were defined in Figures 1 and 2. Colour codes are used to illustrate the various periods based on degree of possibility, or likelihood, of occurrence. Purple indicates no possibility of occurrence, blue indicates low possibility, orange means some possibility, and red is high possibility. The information shown on the figure is meant for educational purposes and not a clinical guideline.


Some key points on Figure 3:

  • During the primary stage, a chancre (painless sore) can develop where syphilis entered the body. It is often not noticeable and often appears in the genital area but may be on the lips or mouth. It will go away on its on within a few weeks, but syphilis will continue to progress. Taken from SmartSexResource.
  • A swab test can be performed with the presence of a chancre sore which although typical, is not always present and a chancre can easily go unnoticed. A swab test directly detects the presence of the syphilis bacterium at the site of infection through microscopic examination of the collected sample. A blood test (described more below) is often conducted along with a swab test.
  • During the secondary stage, a non-itchy rash can develop anywhere from 14 to 90 days after sexual contact. The rash can appear anywhere on the body, but it is most often found on the chest, belly, genitals, palms of the hands and soles of the feet. The rash usually disappears, but it can come back months later. Other symptoms may include headache, fever, hair loss, swollen lymph nodes and bumps or patches inside the mouth, anus, penis/external genitals, or vagina/internal genitals. Taken from SmartSexResource.
  • Since blood tests are more commonly performed compared to swab tests, a syphilis diagnosis can be missed during the primary stage. This is because there may not be enough antibodies built up in the blood to be detected by the testing technology which would produce a false negative result. Meanwhile, the person could still pass on syphilis during this time. Most swab tests are accurate once you have symptoms. Blood tests are the most accurate 90 days after you come in contact with syphilis. Taken from SmartSexResource.


It becomes clear that there are no solid rules around pinpointing measures of time for the incubation period, stages of symptoms, window period, and testing window. However, it is important to know that if a person is sexually active with multiple partners to get a regular blood test every three months.

Detailed conversations between individuals and healthcare providers about things like known times of exposure, the presence of symptoms, and degree/nature of sexual activity can help diagnose and treat syphilis in a timely manner. Having knowledge of the various periods of syphilis can help facilitate those conversations.

Stay tuned for Part 2.

Read about the Blog Series Introduction.


To learn some basics of syphilis:


BC Centre for Disease Control Health Info

BC Syphilis Action Plan Refresh, 2023-2025


Interesting reads related to syphilis:

Research Update: Rapid HIV and syphilis test now approved for clinical use

The BCCDC Position Statement on Doxycycline as Prophylaxis for Sexually Transmitted Infections

CATIE Webinar – Doxy-PEP and doxy-PrEP: Pill to prevent syphilis

CATIE News – Study finds some people with HIV are at greater risk for STI’s


Questions? Get in touch:

Monte Strong, Research and Evaluation Assistant: monte [at]