The STI superbug you’ve probably never heard of

By Sara Kloepfer

A relatively new sexually transmitted infection (STI) is becoming increasingly common, and chances are, you probably haven’t even heard of it: mycoplasma genitalium, or MG.

Unlike other STIs, MG is concerning primarily because of the other conditions it can cause. Since it is tricky to diagnose, MG often goes untreated, which can lead to urethritis in men and women and cervicitis and pelvic inflammatory disease (PID) in women. The British Association of Sexual Health and HIV (BASHH) reported that MG could become a superbug within the next five years. A superbug is a strain of bacteria that has become resistant to antibiotic drugs, making it especially difficult to treat. Mycoplasma genitalium is often misdiagnosed as chlamydia, causing doctors to prescribe the wrong antibiotics, which creates antibiotic resistance in MG infections. Even though MG is on the rise globally, it is little known and under-diagnosed.

Before you freak out, take a deep breath and read all the facts:

What exactly is MG? 

Mycoplasma genitalium is a type of bacteria that can cause an STI. It is passed through bodily secretions, the way chlamydia and gonorrhea are. According to the Centers for Disease Control and Prevention (CDC), it was first discovered in the early 1980s, but the connection between MG and sexual activity did not come until the mid-1990s. 

How common is MG? 

According to the CDC, MG has surpassed gonorrhea in becoming the third most common STI among young people in the United States, behind chlamydia and trichomoniasis. An estimated 2-4% of Americans have MG. Though both men and women are at risk, the rates of infection for women are slightly higher.

How do you get MG? 

Like pretty much every other STI, MG is transmitted through unprotected sex, which can include genital-to-genital contact, anal, and oral sex. 

What are the symptoms? 

Like many other STIs, MG often has no symptoms — especially in women. If a woman does experience symptoms, they are usually similar to other gynecological issues, such as chlamydia: persistent vaginal irritation, pain in the pelvic area or during sex, fever, abnormal discharge, or bleeding after sex or between periods. In men, symptoms include watery discharge from the penis, and pain during urination. Although each case varies, it usually takes between 2-35 days after infection for symptoms to develop. 

How serious are the side effects? 

Mycoplasma genitalium is the second most common cause of urethritis (inflammation of the urethra) in men and women. In women, MG can double the risk of cervicitis (inflammation of the cervix), PID (an infection of the reproductive organs), spontaneous abortion, and pre-term delivery. The increased risk of PID is especially concerning, as severe cases can lead to infertility. 

How do I know if I have MG? 

Mycoplasma genitalium is especially difficult to diagnose for multiple reasons. Not only are the symptoms easily mistaken for other infections, but the testing process itself is not widely standardized or accessible. Mycoplasma genitalium is a slow-growing organism, so traditional testing methods, which require isolating and culturing bacteria from a sample, can take up to six months. This time-consuming process is not effective when immediate treatment is necessary.

Instead, doctors use nucleic acid amplification testing (NAAT), which tests urine, urethral, vaginal, and cervical swabs. However, NAAT for diagnosing MG was developed primarily for research, and, as a result, is only available in commercial laboratories or large university hospitals, making the testing inaccessible for most patients. Unlike other STIs, there is no diagnostic test for MG approved by the Food and Drug Administration (FDA) for use in the United States. Meanwhile, other countries, including Britain, provide tests through government labs. Currently, at least two companies are in the process of securing FDA approval, which should happen in the next 12-18 months. An alternative solution is to use a home test from a private company, such as myLAB (note that these options are not FDA approved). 

If you have symptoms of MG, or have been diagnosed with chlamydia and the symptoms do not go away with standard antibiotic treatment, ask your healthcare provider about testing. Mycoplasma genitalium is also very likely in cases of persistent or recurrent urethritis, cervicitis, or PID. It is important to note that MG can be asymptomatic for years, and doctors cannot know when a patient was exposed. So if you are in a monogamous relationship and you or your partner is diagnosed with MG, do not jump to conclusions. You can also get MG again even if you have already received treatment, so make sure your partner is tested and treated as well. 

How do I treat MG?  

Treating MG presents a number of challenges. Mycoplasma genitalium has rapidly developed a resistance to azithromycin, a common antibiotic used for bacterial infections, and is now showing resistance to other antibiotics used as a second-line defense. Mycoplasma genitalium is difficult to treat because it is not built like other infections — common antibiotics like penicillin kill bacteria by damaging a pathogen’s cell walls, but MG bacteria do not even have cell walls to attack. Mycoplasma genitalium also has the smallest-known genome of any free-living bacteria, meaning it can multiply quickly, which leads to a higher chance of error. This high error rate when multiplying translates to a high mutation rate that can outpace antibiotics. 

Another major issue is the misdiagnosis of MG. It is easy to mistakenly treat an MG patient for chlamydia, but this only makes MG more resistant to those antibiotics. A healthcare provider might also focus on the conditions caused by MG, but the antibiotics generally used to treat these are not actually effective against MG itself.   

If you are diagnosed with MG, your healthcare provider might first try the antibiotic azithromycin, and if that does not work, they might try the antibiotic moxifloxacin. After one month, you should take another test to ensure the infection is gone, but routine testing is not recommended if you have no symptoms. If you still have MG, you will need further treatment. Treatment failure rates for MG are 50% or more. To put it in perspective, for gonorrhea, a treatment efficacy rate below 95% is considered concerning. MG is not untreatable, but you may have to cycle through several different types of treatments before you are cured. 

How can I prevent MG? 

As with most STIs, condoms and other barrier methods reduce your chance of getting MG, although they cannot guarantee it. If you have been diagnosed with MG, avoid having sex for one week after beginning treatment so that you do not infect others.


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