Mycoplasma genitalium (often called Mgen) infects roughly 1 to 2 percent of the general population in developed countries at any given time. In the United States, that translates to an estimated 3.3 million people between the ages of 14 and 59 carrying the infection, based on national survey data from 2017 to 2018. It’s less common than chlamydia overall, but it’s far from rare, and rates climb sharply in certain groups.
Prevalence in the General Population
The best population-level data for the U.S. comes from the National Health and Nutrition Examination Survey (NHANES), which tested nearly 7,800 people aged 14 to 59. The overall prevalence was 1.7%, with a range suggesting anywhere from 2 million to 5.1 million infections nationwide at a single point in time. A large meta-analysis covering multiple countries found a similar figure: 1.3% in higher-income nations and 3.9% in lower-income ones.
For context, chlamydia is typically detected in around 3 to 7 percent of people screened in clinical settings, making Mgen roughly half as common in most populations studied side by side. But Mgen often flies under the radar because routine STI panels don’t include it, so many infections go undiagnosed entirely.
Rates in Higher-Risk Groups
The picture changes dramatically in sexual health clinic settings. Among men visiting STI clinics with symptoms of urethritis (pain or discharge during urination), nearly 29% tested positive for Mgen in one major U.S. study. Among high-risk women at a Seattle STI clinic, 26% were infected. These numbers are roughly 15 to 20 times higher than the general population rate.
Geographic variation matters too. A multi-country study of women considered at higher risk found Mgen in 22.1% of participants in South Africa, 16.0% in Morocco, and 12.4% in Guatemala. Among men who have sex with men, prevalence ranged from 10% in Malta to 20% in Peru. The pattern is consistent: wherever sexual health risks are concentrated, Mgen prevalence rises substantially.
How It Compares to Other STIs
Mgen is responsible for a surprisingly large share of urethritis cases in men. It accounts for 15 to 20 percent of all non-gonococcal urethritis cases, 20 to 25 percent of cases where chlamydia has been ruled out, and a striking 40 percent of urethritis that keeps coming back after treatment. If you’ve been treated for urethritis and your symptoms won’t go away, Mgen is a leading suspect.
In studies that screen for both infections simultaneously, chlamydia tends to be somewhat more common. One large multicenter study found chlamydia in 5.6% of women and Mgen in 3.4%. Among women with lower reproductive tract symptoms, the gap narrowed: 7.1% for chlamydia versus 3.8% for Mgen. The two infections can also occur at the same time.
Many Infections Cause No Symptoms
A significant portion of people with Mgen have no idea they’re infected. The infection causes both symptomatic and asymptomatic urethritis in men, and in women it can silently persist in the reproductive tract for extended periods. Because there’s no standard screening recommendation for Mgen in people without symptoms, most asymptomatic cases are never detected or treated.
This matters because untreated Mgen in women can lead to pelvic inflammatory disease (PID), which carries serious consequences: scarring of the fallopian tubes, ectopic pregnancy, chronic pelvic pain, and infertility. The risk isn’t theoretical. These are the same complications associated with untreated chlamydia and gonorrhea, and Mgen is increasingly recognized as another cause.
Why Testing Isn’t Routine
Unlike chlamydia and gonorrhea, Mgen isn’t part of standard STI screening panels in most clinics. The FDA-cleared test for Mgen uses nucleic acid amplification technology (the same type of molecular test used for other STIs), and it performs well. For self-collected vaginal swabs, it’s about 99% sensitive and 98.5% specific. For male urethral swabs, sensitivity is 98.2% with 99.6% specificity. Male urine samples also work reliably, at around 91% sensitivity.
Female urine samples are the weakest option, detecting only about 78% of infections. If you’re a woman being tested for Mgen, a vaginal swab (even one you collect yourself) is considerably more accurate than a urine test. The testing technology exists and works. The main barrier is that most providers don’t order it unless symptoms persist after standard STI treatment fails.
Growing Antibiotic Resistance
One of the biggest concerns about Mgen isn’t just how common it is, but how difficult it’s becoming to treat. UK surveillance data from 2024 found that 63.6% of Mgen samples carried mutations making them resistant to macrolide antibiotics, the first-line treatment option. That’s up from 62.2% the year before. Resistance to a second class of antibiotics, fluoroquinolones, jumped from 12.1% to 16.7% over the same period.
Even more concerning, 13.7% of samples showed resistance to both drug classes simultaneously, leaving very few treatment options. Resistance rates aren’t uniform across groups. Among men who have sex with men, macrolide resistance reached nearly 80%, compared to about 57% in heterosexual men and 64% in women. Among people who failed their first course of treatment and still tested positive, over 90% had a macrolide-resistant strain.
This resistance trend is a major reason why resistance-guided treatment, where labs test the specific strain for drug susceptibility before choosing an antibiotic, is becoming the preferred approach in countries with access to that testing. Without it, there’s a high chance of prescribing an antibiotic that won’t work, which drives further resistance.
Who Should Consider Getting Tested
Testing is most useful in specific situations: persistent or recurrent urethritis that doesn’t respond to standard treatment, unexplained cervicitis or pelvic inflammatory disease in women, and as part of a workup when chlamydia and gonorrhea tests come back negative but symptoms remain. Sexual partners of someone diagnosed with Mgen should also be tested.
Routine screening of people without symptoms isn’t currently recommended by the CDC, partly because the natural history of asymptomatic infection isn’t fully understood, and partly because of concerns that widespread antibiotic use could accelerate resistance. If you’re symptomatic and your initial STI tests are negative, asking your provider specifically about Mgen testing is reasonable. The test is a simple swab or urine sample, and results typically come back within a few days.