What is Mgen, and why isn’t it in a standard STI screen?

You might have seen “Mgen” mentioned alongside other STIs, or noticed it isn’t on a standard test list, and wondered what it is and whether you should be tested. Mgen (Mycoplasma genitalium) is a common, usually silent sexually transmitted infection — and there’s a good, deliberate reason it’s left off the routine screen. Here’s what it is, and when testing actually makes sense.

What is Mgen?

Mgen is short for Mycoplasma genitalium, a bacterium and one of the smallest known to infect people. It was first identified in the 1980s and is now recognised as a genuine STI, though it’s still less well understood than long-established infections like chlamydia. In many ways it behaves like chlamydia: it infects the same parts of the body, often causes no symptoms, and can lead to similar complications. It’s increasingly common, and a frequent cause of urethritis (inflammation of the urethra) that isn’t explained by chlamydia or gonorrhoea.

At Clinic365 we go beyond the standard screen and can test for Mgen when it’s clinically appropriate. If you want to arrange it, see our Mgen test.

How do you get Mgen?

Mgen is passed on through unprotected vaginal and anal sex, and through genital-to-genital contact. As with other STIs, it’s more likely with a new partner or multiple partners, and condoms reduce the risk. It can affect the urethra in men, and the cervix and urethra in women.

What are the symptoms of Mgen?

Most people with Mgen have no symptoms at all, which is exactly why it spreads quietly. When symptoms do appear, they closely resemble chlamydia.

In men, Mgen is a common cause of urethritis, which can bring:

• discharge from the penis
• pain or burning when passing urine
• discomfort or irritation in the urethra.

In women it’s more often silent, but it can cause:

• unusual vaginal discharge
• pain when passing urine
• pain during sex, or bleeding after sex
• pelvic pain.

Because these overlap so heavily with chlamydia and gonorrhoea, symptoms alone can’t tell you which infection you have — that takes a test. See how the common infections compare in chlamydia vs gonorrhoea.

Why isn’t Mgen in a standard STI screen?

This is the question that brings most people here, and the answer is deliberate, not an oversight. Australian guidelines specifically recommend against screening people who have no symptoms for Mgen. There are two main reasons.

We still don’t fully understand it

Mgen is a relatively recent discovery, and many people carry it without ever developing problems. Because we don’t yet know which silent infections will go on to cause harm and which won’t, testing everyone would mean finding — and treating — a lot of infections that may never have caused any trouble.

Antibiotic resistance

This is the bigger reason. Mgen has become strikingly resistant to the antibiotics used against it: nationally, resistance to azithromycin (long a mainstay treatment) now exceeds 60%, and it’s higher still in some groups. Every unnecessary course of antibiotics pushes that resistance further. Screening and treating people with no symptoms would fuel resistance without a clear health benefit, so the guidelines reserve testing for situations where it genuinely changes care.

That’s why a standard screen focuses on the infections where screening clearly helps — chlamydia, gonorrhoea, syphilis, HIV and hepatitis B — and Mgen is tested only when there’s a specific reason. It’s a case of testing smarter, not testing more.

When should you be tested for Mgen?

Testing for Mgen is recommended when the result will actually guide treatment, including if you:

• have symptoms of urethritis or cervicitis (discharge, pain passing urine) that persist or aren’t explained by chlamydia or gonorrhoea
• have pelvic inflammatory disease (PID) or unexplained pelvic pain
• have post-coital bleeding (bleeding after sex)
• are the sexual partner of someone diagnosed with Mgen.

If that sounds like you, a Specialist GP can arrange the right test. If you simply want a routine check-up and have no symptoms, a standard STI screen is the appropriate choice.

How is Mgen tested for?

The test itself is straightforward. In men it’s usually a first-pass urine sample (the first part of the stream); in women, it’s a self-collected vaginal swab, which is quick and private. The laboratory uses a NAAT — a sensitive DNA-based test — to detect the bacterium. Crucially, the same sample can also be checked for macrolide resistance, so if Mgen is found, your doctor already has a good idea of which antibiotics are likely to work. That single step is what makes resistance-guided treatment possible, and it’s a key reason Mgen is best handled through proper testing rather than a guessed course of antibiotics.

Treatment and antibiotic resistance

Mgen is treatable, but it’s more complicated than a typical STI because of resistance, so it’s worth treating carefully rather than reaching for the usual antibiotics. Best-practice treatment is resistance-guided: the same sample used to diagnose Mgen is also checked to see which antibiotics it’s likely to respond to, and treatment is chosen accordingly. This approach has lifted first-line cure rates from around 60% to over 90%.

Because of resistance, a few principles matter:

• treatment usually involves a specific combination or sequence of antibiotics chosen by your doctor, not a single standard dose
• you’ll need to finish the full course and avoid sex until it’s complete
• a follow-up “test of cure” a few weeks later confirms the infection has gone
• partners should be tested and treated too.

It’s not something to self-treat or treat on spec: using the wrong antibiotic can make resistance worse, both for you and more broadly. That’s a big part of why Mgen is handled through proper testing rather than guesswork.

Complications if left untreated

Like chlamydia, untreated Mgen can cause problems, particularly in women. It’s associated with pelvic inflammatory disease, which can cause pelvic pain and may affect fertility, and in pregnancy it’s linked to a higher risk of miscarriage and preterm birth. In men it’s a common cause of persistent urethritis. These risks are exactly why Mgen is taken seriously when symptoms or a partner’s diagnosis point to it — even though blanket screening isn’t recommended.

The bottom line: Mgen isn’t missing from the standard screen by accident. For most people with no symptoms, not testing is the right call. But if you have symptoms that won’t settle, or a partner has been diagnosed, it’s worth testing properly — and a Specialist GP can arrange the right test, including resistance testing, and guide treatment that actually works.