What is Mycoplasma genitalium ? M . genitalium is an emerging sexually transmitted infection ( STI ). It is the most recently discovered bacterial STI and was first isolated in 1980 from urethral specimens of men diagnosed with non-gonococcal urethritis ( NGU ).¹ It is bottle shaped and at 200-300 nanometres , it is the smallest known living organism capable of self-replication . The ‘ neck ’ of the structure ends in a tip that helps it attach to the epithelial cells of the genital tract . M . genitalium is from a class of bacteria called mollicutes , from the Latin for ‘ soft skin ’, describing the lack of a cell wall .¹

How prevalent is it , and who is at increased risk ? Studies estimate the prevalence of M . genitalium infection in the general population is around 1-2 %, lower than that of chlamydia . 2 , 3 Surveillance of the infection in sexual health services began in 2015 , and rates have increased significantly from 0.1 % in 2015 to 12.8 % in 2022 . ⁴ A recent audit in a sexual health service in Liverpool demonstrated a 11.1 % prevalence in men * and 12.9 % in women *. ⁵

In common with many STIs , risk factors include younger age when starting to have sex , non-white ethnicity , smoking and increasing number of sexual partners . It is also associated with the detection of other STIs , with chlamydia the most frequently diagnosed co-infection .

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How is it transmitted ? M . genitalium can be transmitted via unprotected sex . Most cases occur as a result of genital-to-genital direct mucosal contact , but there is evidence that infection can occur in the rectum following transmission via penile-anal contact . Carriage in the throat is rare .¹

What are the symptoms ? Most people infected with M . genitalium will have no symptoms . In those who do , symptoms can be similar to those for other STIs such as chlamydia or gonorrhoea ( see Table 1 ). Infection is closely associated with NGU and is thought to contribute to between 10 % and 35 % of non-chlamydial NGU in men . NGU is inflammation of the urethra with a cause other than gonorrhoea , diagnosed by examining a sample from a urethral swab under a microscope .

M . genitalium is also associated with cervicitis and pelvic inflammatory disease ( PID ) in 10 % -25 % of cases . ⁶ PID occurs as a result of infection ascending to the upper reproductive tract in women and can lead to increased risk of ectopic pregnancy and infertility if left untreated .

How is M . genitalium diagnosed ? Diagnosis is made via nucleic acid amplification testing ( NAAT ) on urine samples or vaginal swabs . As the organism has no cell wall it is not seen on gram-stain microscopy , unlike other STIs including gonorrhoea . This

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