Syphilis Is Rising Fast in Australia, Especially Among Women

Australia's newest national snapshot of sexual health shows syphilis and gonorrhoea rates holding at high levels after a decade of steep increases, with the fastest growth in syphilis now occurring among women. The numbers come from the Kirby Institute at UNSW Sydney, which released its annual data on September 15.

In 2025, Australia recorded 5,986 syphilis diagnoses, 42,393 gonorrhoea diagnoses and 94,184 chlamydia diagnoses. Syphilis and gonorrhoea diagnosis rates have each increased by more than 50 percent over the past ten years. Chlamydia rates have fluctuated but stayed roughly stable, leaving it the most commonly notified STI in the country.

Most infections show no symptoms

One reason STIs keep spreading is that they often show no symptoms. Chlamydia, gonorrhoea and syphilis can all go unnoticed for months, and untreated infections can cause pelvic inflammatory disease, infertility, and pregnancy complications including miscarriage and stillbirth. According to Dr Skye McGregor, the Kirby Institute epidemiologist who led the report, that is exactly why testing and treatment need to be easy to access and why prevention has to reach the communities most affected.

McGregor described sexual health as a normal and important part of overall health and wellbeing, and noted that many STIs have no symptoms but are straightforward to detect and treat. For people who are sexually active, she said, the practical steps are regular testing, early treatment, and honest conversations with partners and health providers about prevention.

Chlamydia is the clearest example. Around half of the country's 94,184 chlamydia diagnoses in 2025 were among people aged 20 to 29, and unlike syphilis and gonorrhoea, diagnosis rates were similar among men and women, suggesting transmission across a broad range of sexual networks. McGregor said regular testing matters most for young adults, who face the highest risk, and that chlamydia is easy to diagnose and simple to treat. Early treatment prevents complications and stops onward transmission.

Syphilis is climbing fastest among women

Men accounted for 78 percent of syphilis diagnoses in 2025, but the infection is increasing far more quickly in women: diagnoses rose 167 percent among women over the past decade, compared with 39 percent among men. The trend carries particular weight because syphilis in pregnancy can pass to the unborn child, causing miscarriage, stillbirth, or congenital syphilis in the newborn. Congenital syphilis can leave infants with lifelong health problems, and in the most severe cases it is fatal.

Australia recorded 14 cases of congenital syphilis in 2025. Over the past decade there have been 113, and 40 ended with the death of the infant. Australia is aiming for zero congenital syphilis cases, and in 2025 syphilis was declared a communicable disease incident of national significance after researchers, community groups and health departments raised the alarm.

McGregor said that with timely screening, syphilis can be cured and transmission prevented, so even one case of congenital syphilis is completely avoidable and unacceptable. National guidelines have recently been updated to recommend a minimum of three syphilis tests during pregnancy, and researchers will be tracking whether the change brings case numbers down.

First Nations Australians remain the most affected group overall. Compared with non-Indigenous Australians, they are diagnosed with chlamydia at more than 2.5 times the rate, gonorrhoea at more than four times the rate, and syphilis at more than six times the rate. Six of the 14 congenital syphilis cases in 2025 were in First Nations infants. Robert Monaghan, manager of the Kirby Institute's Yandamanjang First Nations Health Research Program, attributed the gap to ongoing inequities in access to culturally safe and trusted sexual health services. He pointed to modelling showing that First Nations-focused point-of-care testing programs can more than double the proportion of people treated and cured within two days. Since its 2013 launch, the national point-of-care program is estimated to have reduced both the risk of pelvic inflammatory disease and preterm births among First Nations women in the communities where it operates.

A prevention tool is working for gay and bisexual men

Gay and bisexual men accounted for 78 percent of syphilis and 73 percent of gonorrhoea diagnoses in 2025, which suggests most transmission occurs between men. But in this group the trend is moving in the right direction. Over the past three years, infectious syphilis diagnoses fell 30 percent and 37 percent in HIV-negative and HIV-positive gay and bisexual men respectively, while chlamydia diagnoses fell 31 percent and 26 percent.

Professor Andrew Grulich, who heads the Kirby Institute's HIV Epidemiology and Prevention Program, said the decline likely reflects growing use of doxycycline post-exposure prophylaxis, or doxy-PEP, an oral antibiotic taken after a risk event to prevent those STIs. Use of the practice has spread since the 2023 ASHM consensus statement, and Grulich said wider targeted uptake could drive syphilis and chlamydia down further. The longer-term rise in STIs over the past two decades likely reflects a mix of factors, including more comprehensive screening and the widespread availability of highly effective HIV prevention strategies, he added.

Gonorrhoea diagnoses among gay and bisexual men have stayed relatively stable over the past decade, and for now condoms and regular testing remain the trusted prevention tools, available through sexual health clinics and community-based testing services. Syphilis is curable, chlamydia is easy to treat, and every infection caught early is one that does not get passed on. The full data is available in the Kirby Institute's annual report on Australia's sexual health.