- Syphilis is on the rise across Canada and the U.S., including among heterosexual people
- The infection causes inflammation and sores that heighten the risk of HIV transmission
- HIV diagnoses have increased among heterosexual people in Alberta and nearby U.S. states
Rates of new syphilis diagnoses have been increasing over the past 20 years. As a result, there is now an epidemic of this sexually transmitted infection (STI) across Canada and the U.S. The initial symptoms of syphilis—a sore or chancre on or inside the genitals, mouth or other parts of the body—may be painless or go unnoticed. The germs that cause syphilis (called treponemes) quickly spread from the site of first contact. These germs can attack nerves, eventually causing problems in the ears (hearing loss) and eyes (loss of vision). If left untreated, over time syphilis can cause injury to vital organs, including the brain, bones, heart and circulatory system, liver and kidneys. Syphilis during pregnancy can harm the fetus and baby (congenital syphilis).
Symptoms of syphilis can mimic many other diseases; however, this STI can be easily diagnosed with a simple blood test. Most people can recover with a single course of antibiotic therapy. As syphilis can cause inflammation and sores in the delicate wet (mucosal) tissues that line the genitals, mouth and anus, it can help facilitate the entry of HIV into the body.
Across North America, rates of syphilis diagnoses among heterosexual people are on the rise. As mentioned, because of the effects of syphilis on mucosal tissue, having syphilis can increase the risk of acquiring HIV. What’s more, according to a team of Canadian and American scientists, “syphilis and HIV share overlapping transmission pathways, and both can be amplified within sexual networks encompassing multiple partners, transactional sex and substance use.” The team states that “in the early 21st century, syphilis was largely concentrated [among some gay, bisexual and other men who have sex with men] before expanding into heterosexual networks, particularly among individuals facing social and economic vulnerabilities, including homelessness and substance use. A similar shift in HIV transmission could emerge if prevention efforts fail to reach those at risk.”
An increase in HIV diagnoses
A team of researchers in Washington state found that there was a sustained recent increase in HIV diagnoses among people born in the U.S. who reported having only heterosexual contact. As outbreaks and epidemics do not stay in one place, the Washington state researchers reached out to other researchers to find out what was happening with new HIV diagnoses among heterosexual people in the following nearby areas:
- Alberta
- California
- Idaho
- Oregon
The team compared rates of HIV diagnoses in the years 2018-2022 to 2023. They found that in 2023 HIV diagnoses increased by 82% in Oregon, 82% in Washington state, and 32% in Alberta. There was no large increase in Idaho (where diagnoses fell by 29%) or California (where they rose by 12%).
From 2018-2022, in all five regions studied, heterosexual people comprised 11% of HIV diagnoses. However, in 2023, heterosexual people comprised 17% of all HIV diagnoses.
Researchers noted that in the five years prior to their HIV diagnosis, these new cases were more likely than not to have had a history of gonorrhea or syphilis.
The researchers stated that there was “no commensurate increase in [HIV infections] among people who reported a history of injection drug use in Oregon and Washington [during the study period].”
Bear in mind
The research team is experienced in studying outbreaks and epidemics. They stated that the large increase in new HIV diagnoses “suggests this change represents a change in transmission rather than changes in testing or data collection.”
What’s more, the researchers recommended that public health and medical authorities in other places that have observed an increase in syphilis “should be vigilant for changes in related conditions,” such as HIV.
They also stated that with the increase in reported heterosexual HIV transmission, “expanded HIV and sexually transmitted infection screening and targeted prevention and intervention strategies will be essential to mitigate further transmission.”
—Sean R. Hosein
Resources
Winnipeg researchers warn about rising cases of syphilis-related stillbirths – CATIE News
Views from the front lines: Congenital syphilis – CATIE
Congenital syphilis – NCCID
Early access to syphilis screening and treatment needed to prevent stillbirths – CATIE News
Rapid combined syphilis-HIV testing found accurate and useful in an Alberta study – CATIE News
Alberta study underscores the importance of syphilis testing in people who use stimulants – CATIE News
New HIV infections in Manitoba intersect with housing and methamphetamine use – CATIE News
Understanding the impact of the antibiotic doxycycline on the sexual well-being of users – CATIE News
REFERENCE:
Erly S, Troupe D, Capizzi J, et al. Increase in heterosexual transmission of HIV in international Pacific Northwest region (United States and Canada). AIDS. 2025 Sep 1;39(11):1666-1668.