A Mycoplasma genitalium (Mgen) test of cure is a repeat NAAT done 3-4 weeks after you finish treatment to confirm the bacterium is gone. It matters because macrolide resistance now causes the standard single-dose azithromycin regimen to fail often, so a follow-up test catches treatment failures that would otherwise keep spreading and causing symptoms CDC, 2021.
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 |
What is a Mgen test of cure, and why does it exist?
A test of cure (TOC) is simply repeating the diagnostic test after treatment to prove the infection cleared. For most bacterial STIs, clinicians don't routinely do this — they assume the antibiotics worked. Mgen is the exception, because of resistance.
Mgen is an unusual bug: it lacks a cell wall, so beta-lactam antibiotics like penicillins and cephalosporins are useless against it. That biological quirk, plus its slow growth, has left only a narrow set of drugs that work, and the bacterium has been steadily beating them. Macrolide-resistance mutations now exceed 50% in many areas, with one US STI clinic reporting over 62%. The old reflex of a single azithromycin dose frequently fails. Since you can't assume the drug worked, a test of cure tells you whether it didn't.
This is the idea behind why awareness is key in mg diagnosis and treatment: the infection is quiet, the resistance is real, and confirming success means looking again. For the full picture of the organism itself, see our overview of mycoplasma genitalium.
How a Mgen test of cure is done
The test of cure uses the same method as the original diagnosis: an FDA-cleared nucleic acid amplification test (NAAT). NAAT detects the bacterium's genetic material, which is the only reliable way to find Mgen — it's too fastidious to grow in routine culture.
The sample depends on your anatomy and what was tested the first time. Options include a first-catch urine specimen, a urethral or penile-meatal swab, an endocervical swab, or a self-collected vaginal swab. Self-collected vaginal swabs perform well, so you usually don't need a speculum exam just for this.
Macrolide-resistance testing — the lab assay that tells your clinician whether your strain will respond to azithromycin — is not commercially available in the US. That gap puts a lot of weight on the test of cure. Without a resistance result up front, the follow-up NAAT is often the first concrete signal of whether your treatment worked NYSDOH.
When to do the test of cure after treatment
Timing is the part most pages get wrong. Do the test of cure 3-4 weeks after you complete the antibiotic course, not sooner. Testing too early gives false positives, because NAAT can still pick up fragments of dead bacterial DNA before they fully clear, making a successful treatment look like a failure.
Don't confuse this with the window after a new exposure. If you're testing because of recent sexual contact rather than confirming a cure, the relevant timing is different — see our guide on when to test after exposure. The 3-4 week TOC clock starts the day you take your last pill, not the day of exposure.
Who should be tested for Mgen at all
Mgen is not part of routine screening. There is no recommendation to test asymptomatic people, and a standard STI panel usually doesn't include it. Testing is reserved for people with symptoms or signs that point to it:
- Men with recurrent or persistent non-gonococcal urethritis (NGU) — urethral discharge, burning, or irritation that didn't clear after treatment for chlamydia and gonorrhea.
- Women with recurrent cervicitis — inflammation of the cervix that keeps coming back despite treatment, sometimes with abnormal discharge or bleeding.
- Anyone whose symptoms persist after a course of antibiotics, which is itself a red flag for a resistant strain.
If you were diagnosed and treated, you need a test of cure whether or not your symptoms resolved, since clearing symptoms doesn't always mean clearing the bacterium.
What getting tested is actually like
The visit is undramatic. Most Mgen samples are collected in minutes — you urinate into a cup or do a self-collected swab in a private bathroom, hand it off, and leave. There's no fasting, no needle for the NAAT itself, and results are usually back in a few days. Testing is free or low-cost at health departments, Planned Parenthood, and Title X clinics, and you can get tested through several routes.
Not every lab or at-home kit offers a dedicated Mgen NAAT. A standard panel typically won't catch it, so you specifically need the M. genitalium test ordered. If you're shopping options, compare testing providers to confirm Mgen is included before you pay.
| Sample type | Who it suits | Notes |
|---|---|---|
| First-catch urine | Men; also an option for women | Easiest; collect the first part of the stream |
| Self-collected vaginal swab | Women | Performs well; no speculum needed |
| Urethral / penile-meatal swab | Men, clinic-collected | Used during an exam for symptoms |
| Endocervical swab | Women, during pelvic exam | Collected if an exam is already happening |
Reading your test of cure results
A negative result on a properly timed test of cure means the treatment worked and the infection cleared. That ends the episode for you.
A positive result means the bacterium is still there, which almost always indicates a resistant strain or reinfection rather than a flaw in how you took your medicine (assuming you finished the full course). Given how common macrolide resistance is, persistence happens often enough that the test of cure exists to catch it. A positive TOC tells your clinician to move to the next, stronger step.
If your test of cure is positive
Mgen now needs resistance-guided treatment: doxycycline first to lower the bacterial load, then azithromycin if the strain is macrolide-susceptible or moxifloxacin if it's resistant. A persistent infection usually means stepping up to the moxifloxacin pathway. Don't self-treat or reuse leftover antibiotics — get the regimen from a clinician. Finish every dose even once you feel better, and ask whether your partner needs treatment so you don't pass it back and forth.
When to see a clinician
See a clinician if your symptoms persist or come back after treatment, if your test of cure is positive, or if you develop new symptoms like pelvic pain, painful urination, or unusual discharge. Untreated or resistant Mgen can lead to ongoing inflammation and, in women, pelvic inflammatory disease — read more on mgen complications. Clinics handle this diagnosis daily.