Mycoplasma genitalium — often shortened to MGen — is a bacterial sexually transmitted infection. It causes urethritis in men and can cause cervicitis and pelvic inflammatory disease in women.
It is a relatively recently recognised pathogen, and awareness of it lags well behind chlamydia and gonorrhoea.
Why It Gets Missed
Two reasons, and both matter if you are buying a test kit.
It is not in most panels. Standard STI screens and most home testing kits cover chlamydia and gonorrhoea, sometimes with syphilis and HIV. MGen requires a specific test that many services do not offer routinely.
Testing is targeted rather than universal. UK guidance generally recommends testing for MGen in people with symptoms of urethritis or pelvic inflammatory disease, and in partners of people who test positive — rather than screening everyone. That is a deliberate approach, partly to avoid treating asymptomatic infections with antibiotics unnecessarily.
The Symptom Pattern That Should Prompt It
The classic scenario: urethral discharge, discomfort passing urine or pelvic pain, treated for chlamydia, and the symptoms persist. Persistent or recurrent urethritis after treatment is exactly the situation where MGen should be considered.
If that describes you, ask specifically. Do not simply take another course of the same antibiotic.
Antibiotic Resistance Is the Real Problem
MGen has developed substantial resistance to azithromycin, which was the original first-line treatment. Treatment now typically involves a longer, sequential regimen, and resistance testing where available guides which antibiotic to use.
This is why self-treating with leftover antibiotics or antibiotics bought online is worse than useless here. Partial treatment of MGen is one of the reliable ways to create resistant infection, both for you and for everyone you subsequently have contact with.
Test of Cure
Because resistance is common, a test of cure after treatment is standard practice for MGen — usually several weeks after finishing. Attend it even if symptoms have resolved. Symptom resolution is not proof of cure, and a persisting resistant infection is exactly what the follow-up test is designed to catch.
Partners
Current partners should be tested and treated, otherwise reinfection is likely and the whole cycle repeats with more antibiotic exposure. Sexual health services can help with partner notification, including anonymously.
What This Means When Comparing Test Kits
If you have persistent symptoms and are choosing between home testing options, check whether MGen is in the panel — and be aware that a negative result on a four-infection kit does not mean nothing is there.
More importantly: persistent symptoms after treatment are a reason to see a sexual health service, not a reason to buy a broader kit. Diagnosis here needs the right test, interpreted alongside your symptoms and treatment history, and increasingly needs resistance testing that a postal kit cannot provide.
The Broader Lesson
Home testing is genuinely useful for routine screening. Where it falls down is exactly here: an unusual or persistent problem that needs a clinician to think about which test to order. Knowing the difference between screening and diagnosis is what stops people cycling through kits while an infection goes untreated.