Sexually transmitted infections are rising and it's feared the extra demand for check-ups means some patients can't access treatment quick enough.

In the first six months of 2023 more than 80,400 STI cases were reported to the National Notifiable Disease Surveillance System, up 23 per cent on the first half of 2022.

So many people have sought help from the Melbourne Sexual Health Centre some have had to wait up to four hours to be seen while others were turned away and referred to different clinics.

"We're seeing more and more people coming to us who we simply can't see," the centre's director and Monash University Professor Christopher Fairley says.

Cases dropped during the COVID-19 pandemic, particularly in Victoria and NSW, but this year have already overtaken the 76,341 reported in the first half of 2019.

Professor Fairley says the biggest cause is patients unable to access treatment at the start of their illness because without it they stay infectious longer and pass it on.

"It's a vicious cycle because if there are more cases next year than they were this year, the services will struggle even more," he says.

It's a similar story at Stonewall Medical Centre in Brisbane where bulk-billed appointments for STI checks on Thursday nights are usually booked out three weeks in advance.

"We've just put on a second doctor for that clinic to try and to keep up with demand," says GP Matthew Barber.

Many of the clinic's patients are well informed about their health but he's worried there could be a lack of testing among the general population.

A common theory behind rising STIs is that it's easier for people to meet new partners via social media however Dr Barber is concerned those in their 50s and 60s who have casual sex can feel embarrassed discussing it with their doctor or aren't aware they need to get tested.

There have been more than 56,500 cases of chlamydia, 20,400 of gonorrhoea and 3300 of recently-acquired syphilis in 2023.

Up to date HIV infection data is not released publicly but there were 522 new cases in 2021, reflecting a decade-long downward trend.

Prof Fairley says while the success of controlling HIV infection has been magnificent, the overall situation for STIs is a public policy failure and more government funding for services is needed.

The rise in cases comes as the federal government prepares the fifth national STI strategy for 2023-2030, designed to add to existing education programs, testing, immunisation, training and research.

Almost $20 million was allocated in the most recent budget to address HIV, other bloodborne viruses and STIs.

The overall rise in infections doesn't surprise Sam Read, who oversees Sexual Health Victoria's school and community education program.

She believes there's been an increase in screening after COVID lockdowns and wonders if the availability of PrEP medication to prevent HIV means some people are less likely to use condoms.

More than a quarter of all STIs are being diagnosed in people aged 20-24 and most chlamydia infections are in young women but Ms Read says they tend to get tested for STIs at the same time as cervical screenings so that could explain the numbers.

Overall, she's troubled by the likelihood that cost and access to sexual healthcare remains a significant barrier for young people, those without Medicare cards like international students and regional Australians.

"They're really, really worried their privacy mightn't be protected and also sometimes the discrimination they might face from other healthcare professionals," she says.

"I think there's ongoing need to educate healthcare providers and education professionals as well to make sure they have an approach that's really inclusive."

Dr Barber urges anyone who has casual sex to get checked at least twice a year and for high risk groups to get tested every three months.