The ‘great imitator’ is back with a vengeance in Canada: What clinicians need to know about the new face of syphilis

“Syphilis is at levels we haven’t seen since the Second World War,” says Dr. Marc Steben, a family physician specializing in sexual health and president of the International Society for Sexually Transmitted Diseases Research (ISSTDR). That's a striking statement as the numbers confirm the resurgence of the “big disease.” According to the latest data available in Canada, cases of infectious syphilis rose from 6,371 in 2018 to 12,135 in 2023. Over the same period, cases of congenital syphilis more than tripled, from 17 to 53.This summer, the Public Health Agency of Canada (PHAC) put the disease back in the spotlight for healthcare professionals with the release of new clinical case studies. Consultations with healthcare professionals revealed “a need to update clinical knowledge,” says Karine LeBlanc, a PHAC spokesperson PHAC, particularly on recognizing the varied presentations of syphilis, interpreting serological tests and adapting treatment to the stage of infection.In Quebec specifically, the trend is much the same. “There won’t really be any surprises. We’re seeing the same trend. Syphilis is on the rise,” warns Karine Blouin, a scientific advisor specializing in syphilis at the Quebec National Institute of Public Health (INSPQ), who is working on the next edition of the Portrait of STBBIs, expected in September. This edition should show a renewed increase, following the impression of stabilization given by the 2024 projections in the previous portrait, published in January 2026.In 2023, Quebec recorded 1,389 cases of infectious syphilis, including 1,172 in men and 213 in women. Men therefore remain by far the majority. But the profile is changing. “We are seeing a shift in epidemiology somewhat more towards women and heterosexual transmission,” notes Blouin. However, she cautions that the relative increases should be interpreted with care, since they are starting from historically very low levels among women, who have recorded around 200 cases per year for the past few years.What's more difficult is pinpointing the cause of the resurgence. PHAC says it does not have national data to distinguish between a genuine increase in transmission, improved screening, or a combination of both. However Dr. Annie-Claude Labbé, a microbiologist and infectious disease specialist at Maisonneuve-Rosemont Hospital, notes the resurgence concerns infectious syphilis—primary, secondary and early latent. “There is definitely community transmission.”Blouin places this increase in the context of a transformed prevention strategy since the arrival of effective HIV treatments. “It was truly a turning point,” she says, mentioning in particular “a general relaxation of prevention efforts,” but noting this is not the sole explanation.Dr. Steben is more categorical. For him, the success of HIV treatments has changed the perception of risk, and people are less careful than they were at the turn of the millennium. “Well, yes, because everything is treatable,” he laments. The return of 'The Great Imitator'The first fictional case presented by PHAC features a 25-year-old man who goes to a sexual health booth at a Pride festival. He has a rash that appeared a week ago. A reactive treponemal test and examination of lesions, particularly on the palms and soles of his feet, lead to a preliminary diagnosis of secondary syphilis.The problem is that the disease can disappear. “You can go through primary syphilis without ever having been diagnosed,” emphasizes Dr. Labbé, who chairs the INSPQ’s Committee on Laboratory Testing Related to STIs and sits on the PHAC’s National Advisory Committee on STIs. The chancre can go unnoticed, be mistaken for something else and then disappear without treatment. Secondary manifestations can, in turn, be subtle before resolving. Then comes the latent phase, without any clinical signs.Hence its nickname. “Syphilis is a great imitator. We have to keep it in mind in our differential diagnosis. All the time,” insists Dr. Labbé. Oral sex adds another pitfall. She regularly sees patients surprised to have contracted syphilis despite using condoms. “When I ask them, ‘Do you also use them for oral sex?’ the answer is 'no.'”Dr. Steben takes the observation further. “We don’t think about it because we haven’t seen it, we haven’t been trained,” he says, noting that outpatient manifestations of the disease are rarely encountered during some training programs. His colleague, Dr. Labbé, is more measured in her assessment. According to her, healthcare professionals are now much more aware of the resurgence of syphilis than they were 10 or 15 years ago.The increase among women is a game changerThat said, the increase among women of childbearing age is of particular concern to Dr. Labbé. “Congenital syphilis is unacceptable,” she maintains. In Quebec, screening is recommended in the first trimester or at the first prenatal visit. But a negative result doesn’t close the case: the infection can be acquired later, and the serological window period can last up to three months. In the presence of a new exposure or risk factors in the woman or her partner, the National Institute of Excellence in Health and Social Services (INESSS) recommends repeating the screening, at a minimum around 28 weeks and at delivery.However, not all cases involve a misdiagnosis. Blouin underlines women who did not receive prenatal care, particularly those in situations of recent immigration or significant socioeconomic vulnerability—drug use, sex work, homelessness, poverty or mental health issues. “Minor cases of error . . . at the clinical level, it’s a minority.” What should raise the alarm bells?An unexplained visual disturbance should also raise suspicion of syphilis. Loss of field of vision or visual acuity, red eye: syphilis should be among the possibilities, says Dr. Labbé. Conversely, when syphilis is diagnosed, ocular symptoms must be investigated. Its presence warrants an ophthalmological evaluation. Ocular involvement changes the treatment, which then switches to intravenous penicillin.Another challenge is the timing of serological testing. After recent exposure or in the presence of symptoms consistent with primary syphilis, a negative result may be premature. In this context, PHAC reminds us that non-treponemal titers can take at least two to four weeks to increase and therefore recommends repeating the test two to four weeks after the initial test.Determining the stage remains crucial. “Syphilis staging relies on integrating epidemiological data, medical history, clinical examination, and the results of additional tests. The stage of the syphilis infection guides treatment and follow-up decisions,” says LeBlanc.As for treatment, there are no major changes. “It’s good old penicillin,” says Dr. Labbé.This article has been translated from its original French and first appeared on our sister site Profession Santé.

The ‘great imitator’ is back with a vengeance in Canada: What clinicians need to know about the new face of syphilis

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