Mycoplasma genitalium can cause real complications when it's missed or undertreated: in women it can drive cervicitis up into pelvic inflammatory disease (PID), and emerging evidence links it to tubal infertility and preterm birth. In men it causes stubborn, recurrent urethritis. The biggest modern threat is antibiotic resistance, which makes the old one-dose cure fail.
rising — guides therapy
doxy → moxifloxacin
| Item | Value |
|---|---|
| US adults infected | ~1–2% |
| Azithromycin resistance | ~50% — rising — guides therapy |
| Often | no symptoms |
| Treatment | resistance-guided — doxy → moxifloxacin |
The essentials: what Mgen is and why it matters
Mycoplasma genitalium — often shortened to Mgen — is one of the smallest known free-living bacteria, and it has an unusual trick: it has no cell wall. That single feature explains a lot of its behavior. Beta-lactam antibiotics like penicillins and cephalosporins kill bacteria by attacking the cell wall, so they do nothing against this organism CDC, 2021. It's now recognized as an emerging cause of urethritis (inflammation of the urethra) in men and cervicitis (inflammation of the cervix) in women. To understand how it spreads and where it lives, see our full overview of mycoplasma genitalium.
The reason Mgen has become a headache for clinicians isn't that it's especially aggressive — it's that it has quietly become a resistance problem. Macrolide-resistance mutations now exceed half of strains in many areas, and topped over 62% in one US STI clinic sample. That means the old approach — a single dose of azithromycin — frequently fails, leaving the infection to smolder and, in some people, to climb into the upper reproductive tract.
Symptoms and the complications to watch for
Mgen is frequently silent, especially in women, which is exactly why complications sneak up. When symptoms do appear, they differ by anatomy. For a side-by-side breakdown, read mgen symptoms in men vs women.
In men
Men typically develop non-gonococcal urethritis (NGU) — urethral discharge and dysuria (burning when you pee) — that is often persistent or keeps coming back after treatment. Recurrent or treatment-resistant NGU is, in fact, one of the strongest clues that Mgen is the culprit rather than chlamydia. Less commonly, the infection can extend to cause epididymitis (inflammation of the coiled tube behind the testicle, which can be painful and, if severe, affect fertility).
In women
In women the organism causes cervicitis, which may show up as abnormal discharge, bleeding between periods or after sex, or no symptoms at all. The concern is what happens when it doesn't stay put. Cervicitis can progress to PID — infection that spreads to the uterus, fallopian tubes and surrounding tissue. PID matters because it can scar the fallopian tubes, and that scarring is the mechanism behind two serious downstream harms.
Proven vs. suspected long-term harms
Honesty about the evidence matters here, so it's worth separating what's established from what's still being studied:
- Cervicitis and urethritis — well established. Mgen is an accepted cause of both.
- PID — supported by good evidence; Mgen is recognized as a cause of pelvic inflammatory disease in women.
- Tubal (tubal-factor) infertility — biologically plausible and supported by emerging data, because the same tubal scarring that follows PID is the route to infertility. The link is still being quantified rather than fully settled.
- Preterm birth and adverse pregnancy outcomes — an emerging, suspected association under active investigation, not a proven cause-and-effect.
- Ectopic pregnancy — a theoretical risk that follows the same tubal-damage pathway as infertility.
The practical takeaway: the most solid links are to inflammation (urethritis, cervicitis) and to PID. The fertility and pregnancy risks are real enough to take seriously and treat promptly, but the science is still maturing — be wary of any source quoting precise risk percentages for them.
Testing: getting the right test, not a standard panel
A standard STI panel usually won't catch Mgen — you need a specific test for it, which is why so many cases go unnoticed. Diagnosis uses an FDA-cleared NAAT (nucleic acid amplification test) run on urine or on a urethral, penile-meatal, endocervical or vaginal swab. Testing is recommended for men with recurrent NGU and women with recurrent cervicitis — the people most likely to be harboring it.
There's an important gap: macrolide-resistance testing should ideally guide therapy, but it isn't commercially available in the US. That limitation shapes treatment, as you'll see below. For how to collect the sample and where to order it, see our guide to mgen testing.
What the experience is actually like: most cases are diagnosed from a simple sample — a urine cup, a self-collected swab, or a quick exam — with results usually back in a few days. Testing is often free or low-cost at health departments, Planned Parenthood and Title X clinics. If you had a specific exposure, timing matters — check when to test after exposure so you don't test too early and get a false negative, then get tested when the window is right.
Treatment: why it's now a two-step plan
Because resistance is so common and resistance testing isn't widely available, current guidance uses a resistance-guided, two-step approach — and it always starts with doxycycline to lower the bacterial load before the second drug. The second step depends on whether the strain is macrolide-susceptible or resistant.
| Scenario | Step 1 | Step 2 |
|---|---|---|
| Macrolide-sensitive strain | Doxycycline 100 mg twice daily for 7 days | Azithromycin 1 g once, then 500 mg daily for 3 days |
| Macrolide-resistant, or resistance testing unavailable | Doxycycline 100 mg twice daily for 7 days | Moxifloxacin 400 mg daily for 7 days |
The reason for the doxycycline-first sequence is mechanical: it knocks down the organism count so the follow-on antibiotic has a better chance of finishing the job NYSDOH/Johns Hopkins. Skipping straight to a single azithromycin dose — the old habit — is what drove resistance in the first place and why it so often fails today.
Treatment reality: this is a defined course of pills, not a one-and-done. Finish every dose even after you feel better, because stopping early is exactly how a partly-treated strain becomes a resistant one. Ask your clinician whether your partner needs treating too, and avoid sex until you've both completed therapy.
Prevention
Condoms used every time lower the risk of getting or passing Mgen, the same way they do for other STIs. Because the infection is often symptom-free, routine testing — especially if you have recurrent urethritis or cervicitis, or new partners — catches what you'd never feel. Partners of symptomatic patients can be tested and treated if positive, which is the single most effective way to stop the ping-pong of reinfection between two people.
When to see a clinician
See a clinician promptly if you have discharge, burning with urination, pelvic or testicular pain, bleeding between periods or after sex, or — importantly — urethritis or cervicitis symptoms that came back or never fully cleared after a previous course of antibiotics. Recurrence is the classic Mgen signature. A diagnosis here is common and treatable; clinics handle it daily, and it says nothing about you as a person.