Mycoplasma genitalium: symptoms, testing and treatment

Most people infected have no symptoms, and BASHH says there is no evidence that screening people without symptoms is of benefit and it is likely to do harm at a population level. When symptoms do occur they depend on the person and the site of infection.

In men, the commonest symptoms are discharge from the penis and urethral irritation, and M. genitalium is strongly associated with non-gonococcal urethritis (NGU), found in 15 to 25% of men with NGU according to BASHH. In women, it is associated with post-coital bleeding and cervicitis. Other symptoms such as vaginal discharge, odour, itch or painful sex may occur but are not specific to M. genitalium.

• Discharge from the penis or burning or irritation when peeing (men).

• Bleeding after sex (women).

• Lower abdominal pain, which may indicate pelvic inflammatory disease.

• Persistent or recurrent urethritis after antibiotic treatment.

• Rectal symptoms (proctitis) in some people, although BASHH says it is only tested for in specific circumstances.

Treatment is with antibiotics chosen by a sexual health clinic. BASHH's 2025 guideline says doxycycline for 7 days followed by azithromycin is recommended where the organism is macrolide-sensitive or resistance status is unknown. Doxycycline on its own has poor efficacy (about 30 to 40%), but reduces the amount of bacteria so the second antibiotic is more likely to work.

Where the organism is macrolide-resistant, or azithromycin has failed, BASHH recommends doxycycline followed by moxifloxacin for 7 days. For complicated infection such as pelvic inflammatory disease or epididymo-orchitis, moxifloxacin is given for 14 days. Doses and combinations are for the clinic to decide, so do not use leftover antibiotics.

The Medicines and Healthcare products Regulatory Agency (MHRA) has restricted fluoroquinolones such as moxifloxacin to situations where no alternative is suitable, and BASHH says patients should be counselled on the risks of damage to tendons, muscles, joints and nerves and on psychiatric side effects. If you are given moxifloxacin, a local NHS leaflet advises avoiding indigestion remedies and medicines containing iron or zinc for two hours before and after each dose, and completing the course.

M. genitalium is a very small bacterium that lacks a cell wall. NHS Borders guidance describes it as the smallest known self-replicating bacterium, and UKHSA says that, because it has no cell wall, it is inherently resistant to antibiotics that target cell wall synthesis, such as penicillin.

It is spread by sexual contact. Like chlamydia and gonorrhoea, it can infect the urethra, cervix and rectum, and BASHH says infections with other bacterial STIs alongside it are common. Carriage in the throat is uncommon.

Diagnosis is by a nucleic acid amplification test (NAAT) on urine, a swab or other samples, because the bacterium is extremely slow growing and cannot be cultured routinely. BASHH recommends testing all positive samples for macrolide resistance, and says a UKHSA reference laboratory offers fluoroquinolone resistance testing for treatment failures.

Testing is targeted rather than routine. BASHH recommends testing people with non-gonococcal urethritis, people with signs and symptoms of pelvic inflammatory disease, and current sexual partners of people who test positive. It suggests testing only if symptoms persist after other infections are ruled out for post-coital bleeding or cervicitis, epididymo-orchitis and proctitis. NHS Borders adds that testing is not part of routine STI tests in Scotland.

BASHH says UK surveillance estimates macrolide resistance at around 62% (highest in gay, bisexual and other men who have sex with men), while UKHSA's 2023 report found 12.1% fluoroquinolone resistance and 10.1% dual resistance in the samples tested. It also reports success rates of 95.4% for azithromycin in macrolide-susceptible infection and 98.3% for moxifloxacin in fluoroquinolone-susceptible infection.

If symptoms continue after treatment, BASHH says to exclude re-infection and check the medicine was taken, and re-testing can be considered in people who remain symptomatic. Because treatment options are limited, BASHH says the pragmatic aim is the resolution of symptoms, and a test of cure is no longer recommended for everyone.

BASHH says people should abstain from sex until 14 days after starting treatment and until symptoms have resolved. Only current partners (including non-regular partners where there is likely to be further sexual contact) should be tested, and treated if positive, with the same antibiotic as the index person unless resistance information suggests otherwise.

Condoms reduce the risk of sexually transmitted infections generally. Surveillance of partners found that 48.2% of women, 31.0% of men who have sex with women and 41.7% of gay, bisexual and other men who have sex with men who reported contact with an infected person were infected.

BASHH says there is a possible increased risk of preterm birth but no association with miscarriage, and that where possible it is advisable to delay treatment until after pregnancy, after an informed discussion with the clinician. Moxifloxacin is contraindicated in pregnancy.

Treatment options in pregnancy are limited, and azithromycin is considered unlikely to increase the risk of birth defects. If you are pregnant or breastfeeding, discuss treatment with the sexual health clinician.

NHS sexual health services provide free, confidential testing and treatment, and are the usual route for persistent urethritis or suspected M. genitalium. Private and online tests are also available.

If you test positive privately, take the result to a sexual health clinic so that treatment can be chosen according to resistance patterns and partners can be informed, because the right antibiotic combination is guided by national guidelines.