Superbug crawls out of the shadows

New treatment options are urgently needed to combat the STI mycoplasma genitalium

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A sexually transmitted superbug affecting up to 400,000 Australians is coming out of hiding thanks to new testing technologies.

The recent TGA approval of two PCR assays for mycoplasma genitalium, a chlamydia-like infection, will finally enable doctors to test for the bug, which is has a prevalence of 1 to 3% in the community.

Associate Professor Catriona Bradshaw, a Melbourne sexual health physician and mycoplasma genitalium researcher, said she anticipated a large escalation in diagnoses as a result.

But unfortunately, the efficacy of both treatments for mycoplasma genitalium is in “a rapid downward slide”, she said.

Mycoplasma genitalium is already resistant to the first-line therapy, azithromycin, in 50% of cases, and up to 80% in men who have sex with other men.

The second-line therapy, moxifloxacin, is now only 80 to 85% effective, down from 100% effectiveness only a decade ago, according to experts.

The PBS doesn’t cover moxifloxacin for this indication, so patients would be out of pocket around $80 to $140 for the week-long course of therapy.

Mycoplasma genitalium has a prevalence of 1 to 3% in the community.

The lack of commercial assay up until now, and a current lack of effective, affordable antimicrobial treatment options, have led to great reluctance for guideline committees to include this organism, Professor Bradshaw said.

“It’s this incredible difficulty that has paralysed the field to a degree and paralysed guidelines committees,” she said.

“It’s a very good example of how a disaster can unravel, hidden from public view,” Professor Bradshaw said.

The Australian STI Management Guidelines currently recommend either one dose of azithromycin treatment, or to seek specialist advice for persistent infection or before treating any complicated presentation.

But Professor Bradshaw said this was out of step with current awareness of antibiotic resistance.

The WHO recommends when the failure rate of any antimicrobial reaches a threshold of 95% the drug treatment must be changed, and “we are way past that with mycoplasma genitalium”, she said.

“We are in a situation where we desperately need new treatment approaches and we desperately need to stop using azithromycin,” she said.

“It is handed out like lolly-water in the STI field. This is a real, tangible example of this microbial resistance manifesting.”

Mycoplasma genitalium is an established cause of non-gonococcal urethritis in men, proctitis, cervicitis and pelvic inflammatory disease in women.

There is also some evidence to suggest it increases the risk of preterm delivery, spontaneous abortion, and lower level evidence suggests it may cause tubal factor infertility.

It’s a very good example of how a disaster can unravel, hidden from public view.

Professor Basil Donovan, a sexual health and public health physician at the Kirby Institute in Sydney, called the development of SpeeDx, a test that also informed clinicians if the strain was drug resistant, a “breakthrough”.

But while testing in symptomatic patients was recommended, screening was not, he said.

Mycoplasma genitalium had an “eerie propensity” to develop resistance, which was strange because it was among the bacterium with the smallest genome ever found, Professor Donovan said.

“So you would think it would be very dumb and very stable, but it’s not. It’s a very dynamic one,” he said.

But it was not as nasty as superbugs such as golden staph or multidrug-resistant tuberculosis, he added.

A test of cure is recommended at least two weeks after treatment is completed, and a retest should be done three months after exposure.