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The bacterium Mycoplasma genitalium (MG) is sexually transmitted and can cause inflammation of the urinary and genital tracts in men and women. This germ may also be linked to other problems, including some cases of arthritis and, in women, pelvic inflammatory disease and infertility.

MG appears to be spread by unprotected anal or vaginal intercourse, as it can be detected in fluid samples from the penis, rectum and vagina. So far it has not been detected in fluid samples from the throat.

MG, like other sexually transmitted infections (STIs), can cause inflammation of delicate genital tissue. Such inflammation can make the genitals more susceptible to infection with other STIs, including HIV.

In high-income countries, overall rates of MG infection appear to be low, ranging between 1% and 3%. Several studies have found that rates of MG infection tend to be greater among people who seek care for STIs.


Urethritis is an inflammation of the tube (urethra) that carries urine out of the body. Common causes of urethritis are chlamydia and gonorrhea. However, testing of urine and other samples can fail to detect possible causes of urethritis. In such cases, and depending on the degree of distress caused by symptoms, some doctors may treat their patients with a presumed diagnosis of urethritis caused by MG and/or other STIs. In women, MG can cause inflammation of the urethra and cervix (cervicitis) and likely the uterus and the fallopian tubes.

Symptoms of urethritis in men can include one or more of the following:

  • frequent urination or the feeling of having to urinate frequently
  • a burning sensation while urinating
  • pain during intercourse or on ejaculation
  • discharge from the penis

Symptoms of cervicitis and urethritis in women can include one or more of the following:

  • abdominal pain
  • vaginal pain
  • frequent urination or the feeling of having to urinate frequently
  • pain during intercourse
  • a burning sensation while urinating
  • discharge from the vagina
  • abnormal vaginal bleeding – after intercourse, after menopause, between periods


MG is difficult to grow on a culture in the laboratory, meaning that many patients with an MG infection will have false-negative results for their culture. Some labs may have access to specialized tests that can multiply and then detect the genetic material or DNA of MG. Such tests are called nucleic acid amplification tests (NAAT).

Distribution by gender – MG in men

Here are several studies that sought to assess the incidence (new cases, usually with symptoms) and prevalence (existing cases) of MG among men in high-income countries:

London, UK

In a study with 438 men who have sex with men (MSM), researchers found that about 7% had MG. HIV-positive MSM were significantly more likely (nearly eight-fold) to have MG infection compared to HIV-negative MSM. Among HIV-positive men, MG was more common than the bacteria that cause gonorrhea and chlamydia.

Oslo, Norway

Researchers tested fluid samples from the anus/rectum, penis and throat of 1,778 MSM. They found that 5% had MG; in 70% of these men, it was found in samples taken from the anus/rectum.

Sydney, Australia

In a study of 1,182 men, 8% tested positive for MG.

New Orleans, U.S.

In a study of people who visited a sexual health clinic, researchers found the following rates of MG infection among men who tested negative for chlamydia and gonorrhea:

  • 25% of 97 men with urinary tract symptoms
  • 7% of 184 men without urinary tract symptoms

At the same clinic, 35% of men who were co-infected with chlamydia and who had urinary tract symptoms also had MG co-infection. Among those with urinary tract symptoms due to gonorrhea, 14% were co-infected with MG.

Distribution by gender – MG in women

Here are several studies that sought to assess the incidence (new cases, usually with symptoms) and prevalence (existing cases) of MG among women in high-income countries:

Melbourne, Australia

In this study of 1,110 women aged 16 to 25 years, only 1.3% had detectable MG.

Sydney, Australia

In this study of 527 women, 4% had MG.

Chapel Hill, U.S.

In a study done in North Carolina with 381 women, MG was found in nearly 20%.

Malmo, Sweden

In this study of 5,519 tested women, only 2% had MG.

London, UK

In a study of 2,378 young women, researchers found that about 3% had MG.

Treatment options

Regimens for the treatment of MG can vary depending on the region or medical centre and the severity of the disease. In clinical trials comparing the antibiotics azithromycin and doxycycline, azithromycin resulted in more cures. However, those trials were done several years ago and since then MG may have acquired more tolerance and even resistance to azithromycin. Based on reports and clinical trials, there are at least two possible regimens of azithromycin that doctors can consider, as follows:

  • azithromycin single treatment – one dose of 1 gram taken orally
  • azithromycin extended treatment – 500 mg on the first day followed by 250 mg per day for the next four days

Unfortunately, these two regimens have not been compared against each other in clinical trials so doctors are not certain if one is better than the other.

There is also a 2 gram extended-release formulation of azithromycin (sold as Zmax SR by Pfizer). However, no data on the effectiveness of this dose on MG has been reported.

Increasingly, there have been reports of treatment failure when a single 1 gram dose of azithromycin is used in MG infection. In such cases, some STI experts suggest the use of another antibiotic, moxifloxacin (Avelox), given as 400 mg once daily for between seven to 10 days.

However, it is important to note that reports of MG resistant to both azithromycin and moxifloxacin have been documented.

Our next CATIE News bulletin will focus on antibiotic resistance by MG and a possible emerging therapy.


We thank Marc Steben MD, Institut national de santé publique du Québec, for his helpful discussion, research assistance and expert review.


STIs: What role do they play in HIV transmission?Prevention in Focus

—Sean R. Hosein


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