Merck Manual

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Trichomonas Vaginitis


Oluwatosin Goje

, MD, MSCR, Cleveland Clinic, Lerner College of Medicine of Case Western Reserve University

Last full review/revision Sep 2019| Content last modified Sep 2019
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Trichomonas vaginitis is a vaginal infection due to the protozoa Trichomonas vaginalis.

  • Trichomonas vaginitis is usually sexually transmitted.

  • It can cause a green or yellow discharge, which may be profuse, smell fishy, and be accompanied by itching or irritation.

  • If symptoms suggest a vaginal infection, doctors examine a sample of the discharge and/or fluid from the cervix and test it for microorganisms that can cause infection.

  • Always using a condom can help prevent this infection.

  • One dose of metronidazole or tinidazole taken by mouth cures most women.

The protozoa Trichomonas vaginalis can cause symptoms soon after they enter the vagina, or the protozoa can remain in the vagina or on the cervix (the lower part of the uterus that opens into the vagina) for weeks or months without causing any symptoms. The bladder may also be infected. In men, the protozoa usually cause no symptoms and may remain in the urinary tract for a few days or weeks without causing symptoms. Thus, women and men may be unaware that they are infecting their sex partners.


Trichomonas genital infections (trichomoniasis) are almost always sexually transmitted. Women can be infected through sexual contact with men or women. But men can be infected through sexual contact only with women, not with men. Many people who have this infection have other sexually transmitted diseases.

Because the protozoa can remain in women for a long time without causing symptoms, determining when the infection was acquired and thus from whom can be difficult or impossible.

Trichomoniasis may occur in children. If it does, the cause may be sexual abuse.


Women with Trichomonas vaginitis may have a green or yellow vaginal discharge that is sometimes frothy, profuse, or both. It may smell fishy. The genital area may itch, and the vagina may be red and tender (irritated). As a result, sexual intercourse may be painful. Urination may also be painful if the bladder becomes infected.

The infection can lead to pelvic inflammatory disease and, in pregnant women, preterm labor and delivery.


  • A doctor's evaluation

  • Examination of a sample of the discharge and/or fluid from the cervix

If girls or women have a vaginal discharge that is unusual or that lasts for more than a few days or have other vaginal symptoms, they should see a doctor.

Doctors suspect Trichomonas vaginitis based on symptoms, such as a green or yellow frothy discharge. They then ask questions about the discharge, other symptoms, and possible causes (such as sexually transmitted diseases).

To confirm the diagnosis, doctors do a pelvic examination. While examining the vagina, the doctor takes a sample of the discharge with a cotton-tipped swab. The sample is examined under a microscope. With information from this examination, the doctor can usually identify the microorganism causing the symptoms.

Usually, the doctor also uses a swab to take a sample of fluid from the cervix to test for other sexually transmitted diseases.

To determine whether there are other infections in the pelvis, the doctor checks the uterus and ovaries by inserting the index and middle fingers of one gloved hand into the vagina and pressing on the outside of the lower abdomen with the other hand. If this maneuver causes substantial pain or if a fever is present, other infections may be present.

If children have Trichomonas vaginitis, doctors evaluate them to determine whether sexual abuse could be the cause.


Always using a condom correctly during sexual intercourse can help prevent this infection from being transmitted. However, Trichomonas vaginalis protozoa can infect areas that are not covered by a condom. So condoms do not fully protect people from being infected.


  • Metronidazole or tinidazole

A single dose of metronidazole or tinidazole (antibiotics) taken by mouth cures up to 95% of women if sex partners are treated at the same time. So sex partners should be treated at the same time. People should not drink alcohol for at least 72 hours after they take metronidazole or tinidazole. Drinking alcohol while taking either drug can cause nausea, vomiting, cramps, flushing, and headaches.

During sexual intercourse, condoms should be used until the infection resolves to help prevent transmission of the infection.

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