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Trichomonas is the most common non-viral sexually transmitted infection in the world. It is less common in the UK. However, it is thought that many cases are still not recognised and are not diagnosed. It can be cured with antibiotic treatment.

How do you get trichomoniasis?

Dr Rosemary Leonard MBE

Trichomonas is a protozoan, which is a tiny germ, similar to bacteria. It can infect your genital area. That is, the vagina and urethra in women, and the urethra and sometimes the prostate gland in men. This infection is passed on to other people by having sex (intercourse). This infection does not usually go further into your body and so does not tend to be as serious as some other sexually transmitted infections (STIs). It can also be completely cured, unlike some other STIs.

As with most STIs, it is most common in younger people under the age of 25. In England, there are ten times as many cases of trichomonas in black ethnic minority populations as there are in the general population. Other than in this group of the population, trichomonas infection is very uncommon in the UK. (In England in 2016 for example, there were 7,075 new diagnoses of trichomonas, compared to 202,546 of chlamydia, 36,244 for gonorrhoea and 31,860 for genital herpes.)


  • A vaginal discharge is common. This is typically greeny-yellow and may be 'frothy'. The discharge usually has an unpleasant or fishy smell.
  • Your vagina and vulva may be itchy and uncomfortable. The irritation may extend into your groin. Sex may be painful.
  • You may have pain in the lower part of your tummy (abdomen).
  • It may be sore when you pass urine.
  • No symptoms occur in some women. However, you can still pass on the infection even if you have no symptoms.


  • Discharge from the penis is common.
  • It may be sore when you pass urine.
  • You may pass urine frequently (due to irritation inside the penis).
  • No symptoms occur in most infected men. However, you can still pass on the infection even if you have no symptoms.

Trichomonas infection is usually passed on by having sex (intercourse) with an infected person. As no symptoms may occur in both men and women who are infected, you can pass on the infection without realising it.

  • Pregnancy. If you have untreated trichomonas infection during pregnancy, you have an increased risk of having an early labour and a baby with a low birth weight. You are also more at risk of sepsis after your baby is born.
  • In women it may go on to cause pelvic inflammatory disease, and you are more likely to develop another infection called bacterial vaginosis.
  • In men, trichomonas infection can, rarely, cause an unpleasant infection of the prostate gland (called prostatitis).
  • HIV. If you have untreated trichomonas infection, you have an increased risk of developing HIV infection if you have sex (intercourse) with someone who is infected with HIV.
  • Infertility. In both men and women, trichomonas infection can result in reduced fertility.

It is important to obtain the correct diagnosis, as the same symptoms can be caused by a number of different infections:

  • A sample (swab) of the discharge from your vagina or penis is sent to the laboratory to be tested. This may be taken by a healthcare professional, or they may show you how to take one yourself.
  • Trichomonas is sometimes seen by chance when a smear test is done in women.
  • A sample of urine from men may also show the infection.

If you suspect that you have trichomonas or any other STI then contact your local genitourinary medicine (GUM) clinic or see your GP. In the UK you can go to the local GUM clinic without a referral from your GP. You can ring your local hospital, GP or health authority and ask where the nearest clinic is. Local and national information is also available on the internet - for example, from

An antibiotic medicine called metronidazole is the common treatment. You and your partner should be given treatment at the same time and you should avoid having sex (intercourse) for at least one week after receiving your treatment.

Most people with this infection clear with a short course of metronidazole tablets. Treatment is usually straightforward. Read the leaflet that comes with the tablets for a full list of possible side-effects and cautions. However, the main points to note about metronidazole include:

  • This is usually given as a tablet twice a day for 5-7 days or a higher dose as a single dose.
  • Some people feel sick, and may be sick (vomit) when they take metronidazole. This is less likely to occur if you take the tablets straight after food.
  • A metallic taste is also a common side-effect.
  • Do not drink any alcohol while taking metronidazole and for at least 48 hours after stopping treatment. The interaction with alcohol can cause you to be sick and can cause other problems.
  • Breastfeeding: metronidazole can get into breast milk but is not thought to affect breast-fed babies. However, to play safe, the standard seven-day course with the lower dose is preferred so that a baby does not receive a large dose. If it is essential to use the large 2-gram single dose then breastfeeding should be discontinued for 12-24 hours after taking it. Pregnant women can also use the seven-day course of metronidazole if they have symptoms of trichomonas infection.

Tinidazole is an alternative antibiotic medicine that is sometimes used. This cannot be taken if you are pregnant. Breastfeeding should be avoided when taking tinidazole and also for three days after stopping it.

Yes. Even if they do not have symptoms. You and your partner should be treated at the same time. Anybody you have had sex with in the four weeks before your symptoms started should be treated.

  • After you are treated, you may get the infection back if your sexual partner was not treated, or if you have sex with a new partner who has this infection.
  • Other STIs are more common in people with trichomonas infection. You (and your partner) may be advised to be tested for other infections.

Further reading and references

  • ; British Asociation of Sexual Health and HIV (Feb 2014)

  • ; NICE CKS March 2015 (UK access only)

  • ; Royal College of General Practitioners and British Association for Sexual Health and HIV (Apr 2013)

  • ; Global epidemiology of Trichomonas vaginalis. Sex Transm Infect. 2013 Sep89(6):418-22. doi: 10.1136/sextrans-2013-051075. Epub 2013 Jun 6.

  • ; Trichomoniasis - are we giving the deserved attention to the most common non-viral sexually transmitted disease worldwide? Microb Cell. 2016 Jun 273(9):404-419. doi: 10.15698/mic2016.09.526.

  • ; Public Health England, 2016

  • ; Interventions for trichomoniasis in pregnancy. Cochrane Database Syst Rev. 2011 May 11(5):CD000220. doi: 10.1002/14651858.CD000220.pub2.

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