A new test to detect a superbug similar to chlamydia is being rolled out across the nation – and experts are urging those with symptoms including painful urination to get checked.

Mycoplasma genitalium is thought to affect about 400,000 Australians, but many people have never heard of it, unlike other sexually transmitted infections.

The bacterium can cause painful urination, itching and bleeding in the rectum, and in women has been linked to pelvic inflammatory disease, spontaneous miscarriage and infertility.

Up until recently only a small number of GPs have been able to access Mycoplasma genitalium testing, despite experts believing infection rates are similar to chlamydia (about 1 to 2 per cent of the population).

A new Australian-developed test is being made widely available to doctors and, significantly, it also checks if patients have strains of the infection resistant to the "go-to" antibiotic for bacterial STIs, azithromycin.

Developer SpeeDx said testing facilities were already in place in Victoria, NSW and Queensland, and expected them to be in all other states by the middle of the year.

Mycoplasma genitalium has shown increasing levels of resistance to medication. In some cases, no effective treatment has been available.

Professor Suzanne Garland from the Royal Women's Hospital in Melbourne said resistance to first-line treatments was now about 60 per cent. About 10 per cent of cases were resistant to first and second-line drugs.

She is calling for a surveillance laboratory to be set up to monitor the organism across the nation, as is already the case with HIV, chlamydia and gonorrhoea.

"MG is not [monitored] and we are running out of drugs to treat it," Professor Garland said.

Experts say the disease is most likely to affect the same sexually active groups as similar sexually transmitted infections.

Associate Professor Catriona Bradshaw from the Melbourne Sexual Health Centre said the highest prevalence was among people in their 20s.

In late 2016, Melbourne man Chris Williams was contacted by a recent casual sexual partner to say that he had contracted Mycoplasma genitalium.

Despite not having any symptoms (which isn't unusual), Mr Williams also tested positive for the infection.

He was concerned, as he had never heard of it before – and there was no information on his usual online channels.

"Dr Google told me this was one of the resistant things to first-line treatment," said Mr Williams, 38.

"That made me quite nervous about the future and what it might hold me for me."

Mr Williams said he was treated with a number of antibiotics including doxycycline, as he had a strain that would not respond to other medications – and was cured after about five weeks.

In future, it is hoped Mycoplasma genitalium testing will become part of routine screening for sexually active people

But at present, Professor Bradshaw said, it was recommended only for those with symptoms, due to shortfalls in the limited treatments available.

She said these shortfalls included the bug's propensity to develop resistance, the increasing cost of the drugs and, in rare cases, serious side-effects, including rupture of the Achilles tendon and irregular heartbeat.

"Once we have better information about the infection's impact and a better-tolerated, highly effective treatment, we can recommend widespread screening," Professor Bradshaw said.

She said that while Mycoplasma genitalium had been shown to double the risk of women having pelvic inflammatory disease, spontaneous miscarriage and a pre-term delivery, more work was needed to conclusively prove it caused infertility.

Royal Australian College of General Practitioners president Dr Bastian Seidel said growing treatment resistance emphasised why it was important to put more focus on prevention and safe sex.

The new Mycoplasma genitalium test involves a urine test or a swab of the genital area. A Medicare rebate of $28.65 is available.