The infection
Mycoplasma genitalium is a very small bacterium identified in the 1980s and now recognised as a frequent cause of non-gonococcal urethritis in men and cervicitis in women. Its extremely slow growth long prevented study, and routine diagnosis became possible only with amplification techniques. It now poses a major problem of macrolide resistance, exceeding 50% in many settings.
Key facts
| Organism | Bacterium Mycoplasma genitalium |
|---|---|
| Asymptomatic carriage | Very common |
| Test | NAAT, only where there are symptoms or persistent urethritis |
| Routine screening | Not recommended: it drives resistance |
| Macrolide resistance | Above 50% in many countries |
| Curable | Yes, but antibiotic choice must be guided |
| Vaccine | None |
How it is transmitted
Transmission is sexual, through vaginal and anal sex, and probably oral sex, although throat colonisation is rare. As with other genital bacteria, the frequency of asymptomatic infection keeps it circulating. Carriage without symptoms is common and does not automatically justify treatment.
Symptoms
In men it causes urethritis: scanty clear discharge, discomfort or burning on passing urine, generally milder than with gonorrhoea. In women it can cause cervicitis, bleeding after sex, pelvic pain or pelvic inflammatory disease. In both, infection is very often entirely asymptomatic, which complicates the interpretation of a positive test.
Testing
Diagnosis is by NAAT on urine or a genital swab. Routine screening of people without symptoms is not recommended: it leads to treating carriers who gain nothing and accelerates resistance. Testing is indicated for urethritis or cervicitis, and above all for symptoms persisting after treatment for chlamydia. Where available, macrolide resistance testing is done on the same sample.
Treatment
The usual approach combines an initial phase of doxycycline, reducing the bacterial load, then a second antibiotic chosen on the resistance profile: azithromycin if the strain is macrolide-sensitive, moxifloxacin if not. A repeat test is only useful if symptoms persist after treatment (some countries still offer it routinely). Empirical azithromycin alone, long standard, is now discouraged because it generates resistance.
If left untreated
In women the infection is associated with pelvic inflammatory disease and, in some studies, with tubal infertility and preterm birth, although the evidence is weaker than for chlamydia. In men it sustains recurrent chronic urethritis, often treated repeatedly without a precise diagnosis.
Prevention
- Condoms protect during vaginal and anal sex.
- Do not request a test without symptoms: a positive result in an asymptomatic person creates more problems than it solves.
- Where urethritis persists despite treatment, ask specifically for mycoplasma testing.
- Never restart antibiotics left over from a previous course.
After a diagnosis
- Treat partners only as national guidance directs; recommendations differ between countries.
- Avoid sex until treatment is complete.
- Get retested if symptoms persist, particularly where resistance is known.
- Report any treatment failure: it guides the next choice.
Worth remembering
This is one of the few infections here where testing without symptoms is discouraged. Looking for it routinely means treating people who do not need it and manufacturing resistance.
A little history
Mycoplasma genitalium is the youngest microbe in this section: it was isolated in 1980 in London, at St Mary's Hospital, from the urethra of two men with urethritis of unknown cause, by Joseph Tully and David Taylor-Robinson, who published their discovery in 1981. Extremely hard to grow — several months for a single strain — it remained a laboratory curiosity for twenty years.
It became famous for another reason: in 1995 its genome was among the first to be sequenced in full, and it is the smallest known of any organism able to reproduce on its own, about 580,000 base pairs; in 2008 Craig Venter's team assembled it chemically, the first synthetic bacterial genome. It was the amplification tests of the 2000s that finally made it detectable in routine practice, and its frequency measurable.
British and then American guidelines only recognised it as a cause of STI in its own right in the 2010s, with a new difficulty: half of the strains already resist macrolides in several countries, and susceptibility is now determined by a genetic resistance test even before treating.
How this differs between countries
This is where national guidance diverges most, because no stable international consensus exists.
- Should you test at all? Several countries explicitly advise against testing people without symptoms; others include it in commercial panels sold directly to the public, which results in treating healthy carriers.
- Resistance testing. Macrolide resistance testing on the same sample is routinely available only in some countries; elsewhere treatment is blind.
- Partner treatment. Recommended in some countries, left to clinical judgement in others.
- Antibiotic availability. Moxifloxacin, needed where there is resistance, is not equally accessible or affordable everywhere.
- Online panels. Their spread has sharply increased diagnoses in people without symptoms, with a direct effect on resistance.