Health agencies worry about Mycoplasma genitalium because it's an emerging sexually transmitted bacterium that's increasingly hard to cure. It lacks a cell wall, so common antibiotics fail, and resistance to the drugs that do work — especially macrolides like azithromycin — has climbed sharply. That combination means routine treatment often fails and resistance can spread quietly.
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 |
What Mycoplasma genitalium actually is
Mycoplasma genitalium (often shortened to Mgen or MG) is one of the smallest free-living bacteria known, and it has an unusual trait: it has no cell wall. That detail isn't trivia — it's the root of the problem. Beta-lactam antibiotics, the workhorse penicillins and cephalosporins, kill bacteria by attacking the cell wall. With no wall to attack, those drugs do nothing here. Clinicians are left with a much narrower toolbox, and the bugs have been adapting to it.
Mgen is recognized as a genuine cause of urethritis (inflammation of the urethra, the tube urine passes through) in men and cervicitis (inflammation of the cervix) in women. It's no longer a curiosity — it's a recognized pathogen with its own treatment guideline. For the full background, see our mycoplasma genitalium overview.
Symptoms — and the silent reality
Many people with Mgen have no symptoms at all, which is part of why it spreads undetected. This is especially true in women, where infection can sit silently while still causing inflammation.
In men, Mgen is a leading cause of non-gonococcal urethritis — meaning urethritis not caused by gonorrhea. The hallmark is discharge from the penis and dysuria (a burning sensation when you urinate). What makes Mgen distinctive is its tendency to be persistent or recurrent: symptoms that linger after treatment for something else, or keep coming back, are a classic clue that pushes a clinician to look for it CDC, 2021.
In women, Mgen shows up as cervicitis, which may cause abnormal discharge, bleeding between periods or after sex, or no noticeable symptoms at all. The concern is what happens when it climbs higher into the reproductive tract, which we cover under complications below.
How it spreads
Mgen is sexually transmitted, passed through genital contact during vaginal and other forms of sex. Like other STIs, the people most at risk are those with new or multiple partners and anyone whose partner is infected. Because so many carriers have no symptoms, transmission often happens between people who don't know they're infected.
How it's tested
Diagnosis uses a NAAT (nucleic acid amplification test), a molecular test that detects the bacterium's genetic material. FDA-cleared NAATs can run on a urine sample or on a urethral, penile-meatal, endocervical, or vaginal swab — and the vaginal swab can often be self-collected. In practice that means a urine cup or a quick swab, with results usually back within a few days. Many people get tested free or low-cost at health departments, Planned Parenthood, and Title X clinics.
Mgen is not part of a standard STD panel and there's no routine screening of people without symptoms — current guidance reserves testing for men with recurrent urethritis and women with recurrent cervicitis NYSDOH/Hopkins. If your symptoms keep returning after treatment, ask specifically for a mgen testing, because a general panel won't catch it. If you're trying to figure out timing, our guide on when to test after exposure walks through it, and you can get tested when you're ready.
There's one important gap: macrolide-resistance testing — which would tell your clinician whether azithromycin will work — should guide therapy, but it isn't commercially available in the US. That missing piece is exactly why treatment has gotten complicated.
Treatment: why one pill no longer does it
For years, a single dose of azithromycin cured most cases. That era is ending. Macrolide-resistance mutations now exceed half of all strains in many areas — over 62% in one US STI clinic — so the old single dose frequently fails. The current standard is resistance-guided and two-step, and it always begins with doxycycline to knock down the bacterial load:
| 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 |
Because resistance testing usually isn't available here, many US patients end up on the doxycycline-then-moxifloxacin path. Whatever you're prescribed, finish the entire course even after you feel better — stopping early is one of the surest ways to let a resistant strain survive. Ask whether your partner should be treated too, so you don't pass it back and forth. For a deeper dive into cure rates and the resistance picture, see is mycoplasma genitalium curable? treatment & resistance.
Complications if it's left untreated
In women, untreated Mgen can move from the cervix up into the uterus and fallopian tubes, causing PID (pelvic inflammatory disease — infection of the upper reproductive organs). PID can scar those tubes, and the downstream consequences are serious: it's linked to preterm delivery (giving birth too early) and to infertility, with roughly a twofold increased risk of infertility tied to infection.
In men, the main consequence is persistent or recurrent urethritis — uncomfortable, frustrating, and a sign the infection hasn't been cleared. The longer it goes unrecognized, the more chances it has to be passed on and to develop or spread resistance.
How to prevent it
The same basics that work for other STIs apply here. Condoms used every time lower the risk, and because Mgen so often has no symptoms, testing when you have recurrent symptoms — and treating partners who test positive — is what actually breaks the cycle.
- Use condoms consistently to reduce transmission.
- If you're diagnosed, partners of symptomatic patients can be tested and treated if positive, which lowers your chance of reinfection.
- Don't share leftover antibiotics or self-treat — incomplete or wrong treatment fuels resistance.
- If symptoms keep returning after treatment, ask specifically about Mgen rather than assuming it's the same old problem.
When to see a clinician
Get checked if you have penile discharge or burning with urination that won't quit, abnormal vaginal discharge or bleeding, or pelvic pain — and especially if you were treated for an STI but symptoms came back or never fully went away. That recurrent pattern is the signal that pushes clinicians to test for Mgen specifically. A diagnosis here is common and treatable; clinics handle it daily, and it says nothing about you as a person. If you want to weigh your options, you can compare testing providers.