A little-known sexually transmitted infection is rapidly becoming resistant to drugs, scientists have warned.

Hundreds of thousands of people across the world are believed to carry Mycoplasma genitalium (MG), which can cause infertility and lead to premature births.

Now sexual health researchers in Australia are warning scores of doctors are unaware of the STI as it is 'extraordinarily unrecognised' because it rarely causes symptoms.

However, they claim a new test could allow doctors to treat it before it wreaks havoc and robs young women of their dreams of having a family.

The STI, which can cause pain during sex and bleeding after, has become widespread across the world in the past decade as cases continue to escalate.

Figures suggest one in 100 adults in the UK and US carry the bug, while it is estimated to strike double that in Australia.

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MG, or mycoplasma genitalium, is carried by up to 400,000 Australians, according to researchers' estimates

Its rapid spread across the globe – caused primarily by a lack of awareness - is helping MG become resistant to antibiotics, researchers fear.

The new test, developed by SpeeDz in collaboration with the Melbourne Royal Women's Hospital, hopes to stop that by making doctors more aware of it.

Natika Halil, chief executive of the sexual health charity FPA, explained MG can multiply quickly as a result of illness or stress, which is when most people notice symptoms.

'Mycoplasma genitalium are tiny organisms, or bacteria, that can live in the body without causing any symptoms at all,' she said.

If left untreated the infection can also lead to pelvic inflammatory disease in women, an infection of a woman's reproductive organs that can cause infertility.

The new test will identify the most suitable treatment, according to Dr Alexandra Marceglia, Unit Head of the Sexual Health and Rapid Access Service.

She told 9 News: 'We are no longer guessing in the dark. We can treat patients immediately with the antibiotic we know will work.'

Dr Catriona Bradshaw, sexual health researcher at Monash University, previously told the Sydney Morning Herald of her concerns over MG.

Speaking last year, she said: 'Many doctors don't really know about it, most doctors aren't testing for it, it's extraordinarily unrecognised.'

Dr Bradshaw added the resistance to frontline therapy has occurred over the last decade and has gone unnoticed because of a lack of testing.

MG is a small parasitic bacterium that can infect both men and women, passed through sexual contact or activity, such as foreplay.

Testing is usually undertaken to diagnose a problem if all other tests are inconclusive, for example if tests for chlamydia or gonorrhoea come back negative.

It is often asymptomatic, however other symptoms often include those similar to other STIs, such as pain while urinating, pain during sex, painful or discoursed discharge.

The bug has been around since the 1980s, but it was only classed as an STI in 2015 when scientific research showed it can be passed on through sex.