Mgen reinfection happens when you get re-exposed to Mycoplasma genitalium after a cure, usually through an untreated partner who passes it back. That's different from treatment failure, where the bacteria survived therapy because of antibiotic resistance. The fix depends on which one you're dealing with.
with the right treatment
testing, not symptoms, decides
| Item | Value |
|---|---|
| Curable? | yes — with the right treatment |
| Tested by | NAAT / lab |
| Often | no symptoms |
| If you may have it | get tested — testing, not symptoms, decides |
Why mgen reinfection happens
Mycoplasma genitalium is a tiny, slow-growing bacterium that lacks a cell wall, which is why penicillins and cephalosporins do nothing against it. It's an emerging cause of urethritis in men and cervicitis in women, and it spreads through vaginal, anal, and oral sex. Once you've been treated and the bacteria are gone, you have no lasting immunity. Your body doesn't "remember" it the way it would after some viral infections, so a fresh exposure can plant it right back.
The most common route is a partner who was never tested or treated. If you took your full course but your partner still carries the organism, having sex again hands it straight back to you. That ping-pong cycle can repeat indefinitely until both people are clear, so partner management is the single most important step in stopping recurrence. You can read the full approach on our mgen partner treatment page.
It's not always treatment failure — partners and the retest
People often assume a returning infection means the medicine didn't work. Sometimes that's true, but plenty of "recurrences" are actually new exposures from a partner who was carrying the bacteria the whole time. The clinical picture can look identical, so the distinction matters most for what you do next: a true reinfection calls for treating the partner, while a true treatment failure calls for a different antibiotic.
Partners of symptomatic patients can be tested and treated if they're positive, which directly lowers your reinfection risk CDC, 2021. Finish every pill in your own course even after symptoms fade, and ask your clinician whether your partner needs treatment so you're not trading it back and forth. Skipping the partner step is the most common reason mgen keeps coming back.
How to tell reinfection from a missed cure
Resistance is what makes this organism difficult. Macrolide-resistance mutations now exceed half of strains in many areas, over 62% in one US STI clinic, so the older single dose of azithromycin frequently fails NYSDOH/JHU guideline. When that happens, symptoms never fully resolve or rebound within a few weeks. The bacteria were never knocked out because they shrugged off the drug.
Clinicians reason through it like this:
- Timing. Symptoms that never cleared, or returned soon after finishing pills, point toward resistant bacteria that survived treatment.
- Exposure history. Symptoms that come back weeks or months later, after sex with an untreated or new partner, point toward reinfection.
- Which drug you took. If you only had a single azithromycin dose, failure from macrolide resistance is very plausible given how common those mutations are.
- Partner status. An untreated regular partner makes reinfection far more likely no matter how the timeline looks.
Either way, the recommended treatment is resistance-guided and starts the same: doxycycline 100 mg twice daily for 7 days to lower the bacterial load, then azithromycin (1 g once, then 500 mg daily for 3 days) if the strain is macrolide-susceptible, or moxifloxacin 400 mg daily for 7 days if it's resistant or resistance testing isn't available. Because a true failure usually needs the moxifloxacin arm, telling the two apart changes the prescription.
Preventing mgen reinfection next time
Most reinfections are preventable with a few concrete habits. You want to clear it in both people at once and then reduce future exposure.
- Treat partners. Make sure any partner is tested and treated before you resume sex. This breaks the ping-pong loop.
- Wait until you're both done. Avoid sex until you and your partner have each finished the full course and any recommended cure check has passed.
- Use condoms every time. Condoms used consistently lower transmission risk for sexually transmitted infections, including this one.
- Finish all of it. Stopping pills early because you feel better is a classic mistake that lets the bacteria survive and rebound.
- Test new partners. Routine testing catches infections that cause no symptoms at all, so silent carriers can pass it on without knowing.
If you're not sure whether a recent partner was an exposure risk, our guide on when to test after exposure explains how soon a test can reliably detect an infection.
When to retest after mgen treatment
A cure check (test of cure) confirms the bacteria are actually gone, which matters here because resistance is so common. The diagnostic tool is an FDA-cleared NAAT run on urine or on a urethral, penile-meatal, endocervical, or vaginal swab. Men with recurrent non-gonococcal urethritis and women with recurrent cervicitis should be tested for this organism rather than assuming it's something else.
Macrolide-resistance testing should ideally guide therapy, but it isn't commercially available in the US, so clinicians often default to the resistance-assumed (moxifloxacin) path when the first regimen fails. For how the test works and where to get the right one, see our mgen testing guide. A standard STI panel usually doesn't include mgen, so you have to ask for it specifically. You can also get tested when you're ready.
When to see a clinician
Reach out promptly if any of the following apply, since persistent infection carries real consequences and a delay only lets it spread:
- Symptoms persist or come back after finishing treatment — discharge, burning with urination, or pelvic discomfort.
- You have recurrent urethritis (in men) or recurrent cervicitis (in women) that hasn't been worked up for mgen.
- A partner tests positive or has symptoms, even if you currently feel fine.
- You're concerned about complications. In women, untreated infection is linked to pelvic inflammatory disease (infection that spreads to the uterus and tubes), preterm delivery, and infertility, with about a twofold increased risk; in men, it causes persistent or recurrent urethritis.
A clinician can confirm with the right test, choose the resistance-guided regimen, and coordinate partner treatment so the cycle ends.
Treatment comparison: macrolide-susceptible vs. resistant mgen
| Scenario | First step | Second step |
|---|---|---|
| Macrolide-susceptible (testing shows it'll respond) | 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 |