An estimated half a million people in the UK are living with a sexually transmitted infection that the overwhelming majority have never heard of, public health experts have warned. The bacterial infection, Mycoplasma genitalium (Mgen), is as prevalent as some well-known STIs but remains absent from public consciousness and routine screening.
According to research by LloydsPharmacy Online Doctor, just 15% of Britons are aware of Mgen, despite it affecting around 2% of the sexually active population. For comparison, while chlamydia is a household name—with hotspots like Liverpool reporting over 21,000 cases—the silent spread of Mgen is occurring on a similar scale. A UK study of female students found a baseline prevalence of 3.3% for Mgen, compared to 5.8% for chlamydia.
An elusive infection
Discovered in 1981—74 years after chlamydia—Mycoplasma genitalium is a bacterium that infects the urethra, cervix, and sometimes the rectum. A reliable test for it was only developed in 2017. It is primarily transmitted through unprotected vaginal or anal sex, though researchers are still determining the risk from oral sex.
Like human papillomavirus (HPV) and chlamydia, Mgen is frequently symptomless. When symptoms do appear, typically one to three weeks after infection, they are easily mistaken for other conditions. According to the British Association of Sexual Health, between 50-70% of infected women and 80% of infected men experience no symptoms at all.
For those who do, signs can include pain or burning during urination, unusual vaginal or penile discharge, pelvic pain, bleeding after sex, testicular pain, genital itching, or rectal inflammation.
Potential complications and diagnostic grey areas
Left untreated, Mgen can lead to serious complications. In men, it is linked to epididymitis—a swollen and painful tube behind the testicles—and proctitis, or rectal inflammation. It can also cause persistent urethritis.
In women, the infection can lead to cervicitis (inflammation of the cervix) and pelvic inflammatory disease (PID), which in some cases may affect fertility and cause spotting between periods. Research into the long-term impacts is ongoing; some studies suggest an association between Mgen and PID independent of chlamydia, though one indicated it might not be a major risk factor for clinical PID in the population studied.
Unlike chlamydia, Mgen is not part of standard NHS STI screening. Testing, which involves a vaginal swab, urine sample, or anal/oral swab analysed via PCR technology, is usually only offered if a patient has persistent symptoms. Health officials are cautious about widespread screening due to fears it could drive unnecessary antibiotic use—a critical concern given the infection’s alarming and growing resistance to drugs.
The rising superbug threat
The most pressing challenge with Mgen is its rapid development of antibiotic resistance, which requires the most explanation. The infection is becoming “worryingly resistant” to first-line treatments, with resistance rates exceeding 90% in some regions, prompting experts to warn it could be classed as a “superbug.”
This resistance has forced a shift in treatment strategy. Where a single antibiotic might once have sufficed, clinicians now typically use a two-stage approach. This often involves a course of doxycycline followed by a second antibiotic such as azithromycin or moxifloxacin.
While antibiotics can still be effective, their application must be careful and specific. The situation mirrors broader lessons from efforts to control chlamydia, where large-scale testing programmes have had limited success. The approach to managing Mgen may need to focus more on targeted treatment and antimicrobial stewardship than on mass screening, to prevent its resistance from worsening further.
For the public, the advice remains consistent with general sexual health: using condoms significantly reduces the risk of transmission, and sexually active individuals should seek regular STI testing, particularly if symptoms arise.