4 infections you’ve never heard of: symptoms and risks

They’re four infections of the genitals, and some are more common than you might think:

• Mycoplasma genitalium: an STI caused by bacteria, with 8,265 diagnoses in England in 2025.
• Trichomonas: an STI caused by a tiny parasite, with 9,907 diagnoses in England in 2025.
• Gardnerella: bacteria found in the vagina of more than half of healthy women. It’s linked with bacterial vaginosis (BV), which isn’t classed as an STI.
• Ureaplasma: bacteria that many healthy people carry. It isn’t usually classed as an STI, and it rarely causes problems.

Many people with these infections have no symptoms, which is one reason they go unnoticed. Read more in “Can I still have an STI if I feel fine?”

Mycoplasma genitalium is passed on mainly through vaginal and anal sex. Oral sex is likely to play only a very small part. In England, around 1% to 2% of people have it.

Most people with Mycoplasma genitalium don’t get symptoms. When they do, they can include:

• discharge from the penis, or irritation inside it
• pain when peeing
• bleeding after sex
• pain in the lower tummy, which can be a sign of pelvic inflammatory disease (PID)

Without treatment, it can cause PID. It may also be linked with reactive arthritis and with babies being born early, but the evidence for these is less certain. UK guidelines recommend testing if you have symptoms like these, or if a partner has it.

Treatment depends on whether the bacteria are resistant to antibiotics, which is common. About two thirds of samples in England’s national surveillance in 2025 were resistant to azithromycin, one of the main treatments. Read more in “Is Mycoplasma genitalium gaining antibiotic resistance?”

Trichomonas (Trichomoniasis) is caused by a parasite that infects the vagina and the urethra (the tube you pee through). It’s passed on almost only through sex: vaginal sex, genital skin contact and sharing sex toys. You can’t catch it from towels, baths or toilet seats.

Symptoms can start 5 to 28 days after infection, or much later, and many people never get any. When they do, they can include:

• yellow-green discharge from the vagina, which may look frothy or smell fishy
• itching, soreness or redness in or around the vagina
• discharge from the penis
• pain when peeing, or needing to pee often

Without treatment, Trichomonas can last for months or years. It raises the chance of getting or passing on HIV, and in pregnancy it can cause a baby to be born early or with a low birthweight. It’s treated with an antibiotic called metronidazole. Read more in “Can you get Trichomonas without having sex?”

Gardnerella vaginalis is one of the bacteria that normally live in the vagina, and it’s found in more than half of women who have no problems at all, so finding it on its own doesn’t mean you have BV. Problems start when the balance of bacteria in the vagina changes, causing bacterial vaginosis (BV).

BV isn’t classed as an STI, but sex can trigger it, and it can pass between women during sex. It’s more likely if you’ve changed partner, have an IUD (coil) or use perfumed products in or around your vagina.

Half of women with BV have no symptoms. When there are symptoms, they include:

• discharge with a strong fishy smell, particularly after sex
• discharge that becomes greyish-white, thin and watery

BV doesn’t usually cause itching or soreness, and green, yellow or frothy discharge points to something else, like Trichomonas or Gonorrhoea. BV makes it easier to catch an STI, and in pregnancy there’s a small chance of complications, such as premature birth or miscarriage.

BV is treated with antibiotic tablets, gels or creams, but it often comes back within a few months. A 2025 trial found that treating male partners as well made BV less likely to come back, although UK guidance hasn’t changed yet. Read more in “What is Bacterial Vaginosis?”

Ureaplasma are bacteria that live in the urinary and genital tract of many healthy people, and adults usually pick them up through sex. There are two main types: Ureaplasma urealyticum and Ureaplasma parvum.

Most people who carry Ureaplasma never have any problems. It isn’t usually thought of as an STI, and UK and European guidelines don’t recommend testing people for it routinely, as so many healthy people carry it.

Ureaplasma urealyticum may cause urethritis (inflammation of the urethra) in some men, particularly when there’s a lot of it, and it may play a part when urethritis doesn’t clear up after treatment. Ureaplasma parvum is unlikely to cause urethritis. Other infections, like Chlamydia and Mycoplasma genitalium, are more common causes of these symptoms.

A positive result on its own doesn’t always mean you need treatment. A doctor will look at your symptoms and your other results too. Read more in “Ureaplasma vs Mycoplasma: which is it?”

Better2Know offers:

• Comfort Screen: a urine test for 8 infections, including all four in this blog, plus Chlamydia, Gonorrhoea, Herpes 1 and Herpes 2. You can test from 14 days after sex, with results in 2 days at a clinic, or order a Comfort Screen home test.
• Platinum Screen: our most comprehensive STI screen. It tests for 12 infections, including all four in this blog, HIV and Syphilis, from 28 days after sex, with results in 3 days. If you test before 45 days, a negative HIV result needs a repeat test. A Syphilis test in the first 3 months after sex can miss the infection, so you may need a repeat test.
• Mycoplasma and Trichomonas tests: urine tests from 14 days after sex, with results in 5 days.
• Bacterial Vaginosis test: a vaginal swab taken at a clinic, with results in 4 days.

The Full Screen includes Mycoplasma and Ureaplasma, but not Trichomonas or Gardnerella. Not sure which test you need? Our Patient Care Team is available 24/7 on 020 7099 0955.

Are Gardnerella and Ureaplasma STIs?

They aren’t usually classed as STIs. Gardnerella is linked with BV, which sex can trigger but which isn’t classed as an STI. Ureaplasma is carried by many healthy people and rarely causes problems.

Can men get these infections?

Yes. Men can get Mycoplasma genitalium and Trichomonas, often without symptoms, and can carry Ureaplasma and the bacteria linked with BV.

Can these infections be treated?

Yes. Mycoplasma genitalium, Trichomonas and BV are treated with antibiotics, although Mycoplasma genitalium is often resistant to some of them, and BV often comes back.

Mycoplasma genitalium and Trichomonas are STIs that deserve more attention: both are common, both often cause no symptoms, and both can be treated. Gardnerella and Ureaplasma are carried by many healthy people and are less of a worry than their names suggest. If you have symptoms like unusual discharge or pain when you pee, a test can find out what’s causing them.

Book a Comfort Screen at a clinic near you or order a home test kit from 14 days after sex. Our Patient Care Team is available 24/7 on 020 7099 0955.

Not in the UK? Choose your country from the selector at the top of the page for local tests and prices.

This article originally appeared on 6 August 2021 and was last updated on 30 September 2026.

This article is general information and not a substitute for personal medical advice.

Sources

1. British Association for Sexual Health and HIV, National guideline for the management of infection with Mycoplasma genitalium, 2025. https://www.bashh.org/_userfiles/pages/files/sonietal2025britishassociationofsexualhealthandhivnationalguidelineforthemanagementofinfectionwith.pdf
2. UK Health Security Agency, Mycoplasma genitalium antimicrobial resistance surveillance (MARS) report, 2025, published 30 July 2026. https://www.gov.uk/government/publications/mycoplasma-genitalium-antimicrobial-resistance-surveillance-mars/mars-report-2025
3. UK Health Security Agency, Fingertips sexual and reproductive health profiles: Mycoplasma genitalium and trichomoniasis diagnoses, England, 2025, updated 2 June 2026. https://fingertips.phe.org.uk/profile/sexualhealth
4. British Association for Sexual Health and HIV, United Kingdom national guideline on the management of Trichomonas vaginalis, 2021. https://www.bashh.org/_userfiles/pages/files/resources/tv_2021.pdf
5. NHS, Trichomoniasis, reviewed 16 July 2025. https://www.nhs.uk/conditions/trichomoniasis/
6. Brook, Trichomoniasis, updated 24 September 2026. https://www.brook.org.uk/your-life/trichomoniasis/
7. NHS, Bacterial vaginosis, reviewed 19 June 2026. https://www.nhs.uk/conditions/bacterial-vaginosis/
8. NHS, Vaginal discharge, reviewed 15 February 2024. https://www.nhs.uk/symptoms/vaginal-discharge/
9. British Association for Sexual Health and HIV, UK national guideline for the management of bacterial vaginosis, 2012. https://www.bashh.org/_userfiles/pages/files/resources/bv_2012.pdf
10. Vodstrcil LA, Plummer EL, Fairley CK, et al. Male-partner treatment to prevent recurrence of bacterial vaginosis. New England Journal of Medicine, 2025. https://www.nejm.org/doi/full/10.1056/NEJMoa2405404
11. British Association for Sexual Health and HIV, National guideline on the management of non-gonococcal urethritis, 2026. https://www.bashh.org/_userfiles/pages/files/resources/ngu_2026.pdf
12. Horner P, Donders G, Cusini M, et al. Should we be testing for urogenital Mycoplasma hominis, Ureaplasma parvum and Ureaplasma urealyticum in men and women? European STI Guidelines Editorial Board, 2018. https://iusti.org/wp-content/uploads/2019/12/UrogenitalMycoplasmas.pdf
13. British Association for Sexual Health and HIV, Position statement on the inappropriate use of multiplex testing platforms, updated 9 November 2021. https://www.bashh.org/resources/72/bashh_position_statement_on_the_inappropriate_use_of_multiplex_testing_platforms_and_suboptimal_anti
14. British HIV Association, British Association for Sexual Health and HIV and British Infection Association, Adult HIV testing guidelines, 2020. https://bhiva.org/wp-content/uploads/2024/10/HIV-testing-guidelines-2020.pdf
15. British Association for Sexual Health and HIV, UK guidelines for the management of syphilis, 2024. https://bashh.org/_userfiles/pages/files/syphilis_2024.pdf