Over the last three decades, sexually transmitted infections (STIs) have quietly but steadily climbed in Australia, with bacterial diseases like chlamydia, gonorrhoea, and syphilis spreading across the country. In 2004, just over 35,724 new cases of chlamydia were recorded in Australia, according to federal government data. By 2024, that figure had roughly tripled to more than 102,000 notifications, with infections spread roughly evenly across men and women. "When we look at these data, we can see that chlamydia continues to be the most frequently notified sexually transmissible infection," said Skye McGregor, an epidemiologist with UNSW's Kirby Institute, leading its Australian STI and bloodborne virus surveillance reporting. Gonorrhoea and syphilis have followed a similar trajectory. Annual confirmed cases of the former had risen from 7,047 in 2004 to more than 44,000 in 2024. Syphilis numbers climbed by almost ninefold to 5,969 over the same period. While these infections can be treated with antibiotics and lack the harm potential of other sexual diseases like HIV, they present serious health consequences if they remain undetected, including infertility, congenital transmission and, in the case of syphilis, organ damage. Those first-line treatments are also at risk of soon becoming ineffective, with antimicrobial resistance an expanding global issue. Last year, NSW Health issued a public warning of how gonorrhoea cases resistant to azithromycin and ceftriaxone were growing in the state. "It makes infections harder to treat, which increases the risk of transmission, illness and even death," Dr McGregor said. Though the rise of bacterial STIs is well-documented — long observed by health workers in the country and overseas — exactly why it's happening is something more complex and opaque. 'We can't just point to one thing' While specific populations — including men who have sex with men (MSM) — have long been associated with higher risk, the current data indicates these diseases are proliferating across age, gender and sexuality demographics. "There's a range of factors. We can't just point to one thing and go, 'This is the main reason we're seeing an increase in STIs'," Dr McGregor said. Included in that range of factors are the asymptomatic nature of these bacterial diseases, declining condom use and the unintended impacts of medical innovation. Research has found the widespread availability of pre-exposure prophylaxis (PrEP), a medication that prevents HIV infection, has contributed to more unprotected sex. The most immediate solution to all of this is also the most basic: Safer sexual practices alongside regular, proactive sexual health screenings. "It's really important to have the message of regular, comprehensive testing," Dr McGregor said. But despite that message's simplicity, enacting that change is difficult. One explanation held by Dr McGregor is the lack of awareness of diseases like chlamydia, gonorrhoea and syphilis alongside infection risk factors. This blind spot, she said, stems in part from years of underinvestment, with few public health campaigns and research efforts matching the scale of those targeting HIV or Hepatitis C — diseases where infection rates have dropped in recent years. "It's complex, but if you take into account where the reductions have been, there's a reason for it." Stigma, healthcare costs fuelling screening avoidance While greater investment in prevention initiatives could raise the necessary awareness, other experts say strategies targeting the full spectrum of those at risk are as crucial. "Traditionally we focused on what we call high-risk populations: MSM and Indigenous and so on. But maybe that's not the only group that needs all these resources poured into," Melbourne Sexual Health Centre's Jason Ong said. It's something the sexual health physician and researcher has observed firsthand. In recent years, the number of people seeking screenings has increased. Yet, infection numbers are still continuing to rise. "If you're testing more people, why aren't the STI rates dropping? And so that's also part of that story where, maybe, we're not testing the right populations," he said. "Within certain groups, we know definitely there are people that are not testing." The lack of testing may come down to awareness, but it could also be deliberate avoidance. It's long been established how the stigma surrounding STIs can dissuade someone from seeking medical care. In 2021, Professor Ong co-authored a meta-analysis on what encourages young people from high-income countries to seek STI testing. Both limited awareness and stigma were named as key deterrents. "If we can address that stigma piece, I think that will help a lot so that people can feel comfortable to talk to a doctor about it — and get the proper testing and treatments if needed." But stigma isn't the only barrier to receiving sexual healthcare. The decline of bulk-billing practices within a cost-of-living crisis is keeping people away, too. "It's now expensive for people to go to the GP," said David Lewis, the conjoint professor of the University of Sydney's Sydney Medical School and a sexual health physician in the city's western suburbs. "You can do health promotion, but if you don't make the testing easily accessible for people, then it's a challenge." 'These interventions need to be tailored' One workaround could be importing the strategies embraced for other sexual diseases. At-home rapid tests for HIV have been available in Australia since 2019, with a pilot program providing free access in NSW launched last year. While self-test kits for chlamydia and gonorrhoea were approved for Australian use in November, a similar initiative doesn't exist. But this model of private and instant care could be a blueprint for increasing screening rates. "There's all these other bits of the puzzle. It's not just a question of promotion and education." Professor Lewis said. "It's very hard to shift sexual risk. What programs are successful in doing is often changing health-seeking behaviour," said Burnet Institute's head of public health Mark Stoové. This use of new approaches that centre availability, accessibility and less visibility could be one way forward to circumnavigate those hurdles to testing and sexual healthcare. Pointing to the introduction of point-of-care testing and telehealth in response to HIV and Hepatitis C, Professor Stoové said similar adaptive models of care would — when combined with targeted education and public health messaging — close gaps in testing, in turn lowering infection rates. Any response, he added, needs to be tailored to meet the needs of wherever people are — whether that be financially, culturally, socially or geographically. "Particularly in the space of sexual health education, if we're putting a campaign out there, people need to recognise that the campaign is speaking to them."