Mycoplasma genitalium

What Is Mycoplasma genitalium?

Mycoplasma genitalium — often shortened to M. genitalium or MG — is a bacterium spread through sexual contact. It was first isolated in 1981 and has the smallest genome of any free-living organism that can be grown in pure culture, which is part of why it went unrecognized for so long. Most people who carry it have no symptoms: European guidance puts the asymptomatic share at 40% to 75%. When symptoms do appear they look like chlamydia — discharge, burning when passing urine, irritation — and the two cannot be told apart without a test. The CDC identifies it as the cause of roughly 15% to 20% of non-gonococcal urethritis in men, and finds it in 10% to 30% of women with cervicitis. In women it is also associated with pelvic inflammatory disease: the CDC reports it in 4% to 22% of PID cases.

How is Mycoplasma genitalium spread?

It is passed on mainly by genital-to-genital contact. Transmission through penile-anal sex is also established. Its role in oral sex is not established — the bacterium is uncommon in the throat, and UK and European guidelines judge the contribution of oral sex to be very small; throat testing is not recommended. Because it spreads by contact rather than by fluids alone, condoms reduce the risk without removing it. A partner with no symptoms may still carry it.

How is Mycoplasma genitalium treated?

It is treated with antibiotics, and which antibiotics matters more here than with most infections. The CDC reports that markers for macrolide resistance are found in 44% to 90% of infections and states plainly that a single 1 g dose of azithromycin should not be used. Its guidelines set out a two-stage course — doxycycline followed by moxifloxacin, or by azithromycin where the infection is known to be macrolide-sensitive — and recommend resistance-guided treatment wherever testing allows it. Because treatment failure is common, symptoms that persist afterwards need re-evaluation rather than a repeat of the same course. Guidance on a test of cure differs: BASHH does not require one where symptoms have resolved, while European and Australian guidelines set intervals of roughly two to three weeks after treatment — follow the timing your treating clinician gives you. Advice on partners differs too, between testing them first and treating alongside you, so that is also a clinician decision.