Mycoplasma Genitalium: The Hidden STI You Need to Know About

Mycoplasma genitalium (MG) is a bacterial STI that causes urethritis in men and cervicitis or pelvic inflammatory disease in women. It is more common than gonorrhea in many populations, yet absent from most standard STI panels. Because it is frequently asymptomatic and increasingly antibiotic-resistant, MG is one of the most underdiagnosed infections in sexual health today.

• Up to 70% of MG infections cause no symptoms at all

• MG is not included in routine STI screening at most clinics — you must request it specifically

• Antibiotic resistance rates have reached 50–80% in some regions, complicating treatment

• Untreated MG can cause PID, chronic pelvic pain, and infertility in women

• A test of cure is required 3–4 weeks after completing treatment

What Is Mycoplasma Genitalium?

Mycoplasma genitalium is one of the smallest self-replicating bacteria known to science. First identified in 1981, it was only recognised as a clinically significant STI in the past two decades. It primarily infects the urogenital tract — the urethra in men, and the cervix and upper reproductive tract in women.

What makes MG unusual among STIs is its lack of a cell wall, which makes it naturally resistant to penicillin and other beta-lactam antibiotics. It also multiplies extremely slowly, which contributes to both chronic, hard-to-clear infections and the rapid development of resistance when antibiotics are used incorrectly.

How Common Is It?

MG is more prevalent than most people — and many clinicians — realise. Estimates suggest it affects approximately 1–3% of the general adult population, rising to 4–38% among people seeking STI testing, and 15–25% of patients presenting with urethritis symptoms. In many clinical settings it is more common than gonorrhea, though it receives far less public attention.

It is most prevalent among sexually active adults aged 18–35, particularly those with multiple partners or inconsistent condom use. Because MG is not a notifiable disease in most countries and is excluded from standard screening panels, true prevalence figures are likely an underestimate.

Symptoms: What to Watch For

Symptoms in men

When symptoms do occur in men, they typically include painful or burning urination, a clear or white urethral discharge, and itching or irritation at the tip of the penis. These are signs of urethritis — inflammation of the urethra. Men who have receptive anal sex may also develop proctitis, with rectal pain, discharge, or bleeding. In rarer cases, MG has been associated with epididymitis — pain and swelling in the testicles.

Symptoms in women

In women, MG most commonly causes cervicitis: abnormal vaginal discharge, spotting between periods or after sex, pain during intercourse, and lower abdominal discomfort. If the infection spreads to the upper reproductive tract, it can trigger Pelvic Inflammatory Disease (PID), with severe pelvic pain, fever, and irregular bleeding — a serious complication that can permanently damage fertility.

Asymptomatic infection

Approximately 70% of people with MG have no symptoms at all. This makes it particularly dangerous: people unknowingly transmit the infection to partners, and the bacteria continue to cause inflammation and tissue damage silently over months or years.

How Is It Transmitted?

MG is transmitted primarily through vaginal and anal intercourse. Unlike some STIs, it is not spread through kissing, casual contact, sharing towels, or toilet seats. Risk increases with multiple sexual partners, inconsistent condom use, and the presence of other STIs. Because infected individuals are often asymptomatic for extended periods, transmission frequently occurs without either partner knowing.

Testing: Why You Have to Ask for It

Standard STI panels at most clinics do not include MG testing. This is a significant gap — if you want to be tested, you need to specifically request it. Testing is done using a Nucleic Acid Amplification Test (NAAT), which uses PCR technology to detect MG's genetic material. It is highly accurate and can be performed on a urine sample, urethral swab, vaginal swab, or cervical swab.

Some specialist labs now offer resistance testing alongside NAAT, which simultaneously identifies the presence of MG and checks for macrolide resistance markers. This is increasingly important given the high rates of antibiotic resistance and significantly improves treatment outcomes where available.

Who should get tested?

Testing is recommended for men with persistent or recurrent urethritis that does not respond to standard treatment, women with cervicitis or PID, sexual partners of anyone with a confirmed MG diagnosis, and people with unexplained genital symptoms after other common STIs have been ruled out. Specialist sexual health clinics are the most likely setting to offer MG testing — some primary care providers also offer it, but availability varies.

Treatment: A Two-Step Process

Treatment of MG has become significantly more complex due to rising antibiotic resistance. Current guidelines follow a sequential approach designed to reduce the bacterial load before targeting it with a second antibiotic.

The standard protocol begins with doxycycline (100mg twice daily for 7 days) to reduce bacterial load, followed by either azithromycin (1g initially, then 500mg daily for 3 further days) or moxifloxacin (400mg daily for 7–10 days), depending on resistance testing results and local guidelines.

The resistance problem

Macrolide resistance — resistance to azithromycin — has reached 50–80% in some regions, meaning the standard second-line drug fails in a majority of cases in those areas. Fluoroquinolone resistance (to moxifloxacin) is also increasing. This makes resistance testing before treatment highly valuable where available, and underscores why MG should never be treated with a single-dose azithromycin regimen, which actively promotes resistance.

After treatment

A test of cure should be performed 3–4 weeks after completing antibiotics to confirm the infection has cleared. All recent sexual partners should be informed and tested. Sexual activity should be avoided until both partners have completed treatment and received a negative result.

Complications of Untreated MG

Left untreated, MG can cause serious and lasting harm. In women, the primary risk is Pelvic Inflammatory Disease, which can lead to chronic pelvic pain, tubal scarring, ectopic pregnancy, and infertility. Some studies also suggest associations between MG and preterm birth, though research is ongoing. In men, possible complications include chronic prostatitis and, in rare cases, reactive arthritis. There is also emerging evidence that MG infection may increase susceptibility to HIV acquisition.

Prevention

Preventing MG follows the same principles as preventing other STIs. Consistent and correct condom use during vaginal and anal sex provides significant protection. Open communication with partners about STI testing, reducing the number of concurrent sexual partners, and seeking prompt testing when symptomatic all reduce transmission risk. There is currently no vaccine for MG.

Frequently Asked Questions

Is mycoplasma genitalium the same as chlamydia?

No. MG and chlamydia are distinct bacteria with different biology, treatment protocols, and resistance patterns. They can co-occur, but testing for one does not detect the other. Chlamydia is routinely included in STI panels; MG typically is not.

Can MG go away on its own without treatment?

Spontaneous clearance does occur in some cases, but it is not reliable and cannot be counted on. The infection can persist for months or years, causing ongoing inflammation and complications. Treatment is always recommended when MG is detected.

Can I get MG more than once?

Yes. There is no lasting immunity after MG infection. Re-infection is possible if you have sex with an untreated partner or a new partner who carries MG. This is why partner testing and treatment are essential alongside your own.

Does MG affect fertility?

In women, untreated MG that leads to PID can cause fallopian tube scarring and infertility. The evidence is clearest for women; data on male fertility effects is less conclusive but suggests possible links to chronic prostatitis and epididymitis.

Why is MG not on standard STI panels?

Primarily because MG was only recently recognised as a clinically significant pathogen, and because resistance-guided treatment requires more sophisticated testing infrastructure than most routine screening settings currently have. Guidelines are evolving — coverage in standard panels is expected to increase over the coming years.

Get Tested Today

If you have unexplained genital symptoms, have been treated for urethritis or cervicitis that did not fully resolve, or simply want comprehensive STI coverage, ask specifically for mycoplasma genitalium testing at your next sexual health appointment. Early detection prevents complications and stops transmission to partners.

Related reading: STD Symptoms in Women · Can You Have an STD With No Symptoms? · The Rise of Antibiotic-Resistant STDs · How STDs Affect Pregnancy