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TOPLINE:

Individuals tested for syphilis had a higher risk for subsequent stroke than individuals from the general population, regardless of whether the test result was positive or negative. However, the risk for stroke was similar between those who tested positive and those who tested negative for syphilis.

METHODOLOGY:

• Researchers conducted a population-based cohort study in Denmark and used linked registry and laboratory data from 2000 to 2022 to examine whether syphilis infection increased the risk for subsequent stroke.
• A total of 3593 individuals with a positive syphilis test result were matched with 32,629 individuals from the general population. Separately, 3590 individuals with a negative syphilis test result were matched with the individuals with a positive syphilis test result. The overall median age was 36 years, and 81% of individuals were men.
• To assess the contribution of familial and shared environmental factors, sibling cohorts corresponding to each main cohort were constructed.
• The outcome was the time to the first recorded diagnosis of stroke; the median follow-up duration ranged from 7 to 8 years across cohorts.

TAKEAWAY:

• Individuals with a positive syphilis test had more than a fivefold higher risk for stroke than those from the general population (adjusted hazard ratio [aHR], 5.4; 95% CI, 3.7-7.7); however, the risk for stroke was similar between individuals with a positive test and those with a negative test.
• Individuals with a negative syphilis test also had a higher risk for stroke than those from the general population (aHR, 3.6; 95% CI, 2.3-5.4).
• Siblings of individuals with a positive syphilis test also had a higher risk for stroke than siblings from the general population (aHR, 2.2; 95% CI, 1.4-3.6).

IN PRACTICE:

“This finding suggests that undergoing testing, rather than syphilis infection per se, may serve as a marker of underlying factors associated with stroke risk. The consistency of findings across sibling cohorts supports the role of familial predisposition as well as lifestyle or other confounding factors in stroke risk,” the authors wrote.

SOURCE:

The study was led by Laura Glismann, Statens Serum Institut, Copenhagen, Denmark. It was published online on May 4, 2026, in Clinical Microbiology and Infection.

LIMITATIONS:

Some individuals classified as having negative syphilis test results based solely on a negative nontreponemal test may have had a prior positive result before 2000. The study lacked data on individual lifestyle factors. Stroke diagnoses were based on hospital codes; therefore, minor strokes and transient ischemic attacks may have been missed.

DISCLOSURES:

The study was funded by Copenhagen University Hospital, Bispebjerg, Denmark. Several authors disclosed receiving travel grants, payments for lectures and podcast production, institutional funding, and study materials from; serving on advisory boards and other boards of; or performing contract work for multiple pharmaceutical companies and organizations. One author reported holding shares in Novo and Vertex.

This article was created using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.