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Trichomoniasis ?trik-?-m?-'ni-?-s?s

By J. Allen McCutchan, MD, MSc

Trichomoniasis is a sexually transmitted disease of the vagina or urethra that is caused by the protozoa Trichomonas vaginalis and that causes vaginal irritation and discharge.

  • Women may have a greenish yellow, frothy, fishy-smelling vaginal discharge with irritation and soreness in the genital area.

  • Men usually have no symptoms, but a few have a frothy discharge from the penis and mild pain or discomfort during urination.

  • Examination of a sample of the discharge under a microscope usually enables doctors to identify the infection.

  • A single dose of an antibiotic cures most women, but most men need to take an antibiotic for 5 to 7 days.

Trichomonas vaginalis commonly causes a sexually transmitted disease (STD) of the vagina in women and an STD of the urinary tract in men and women. Women are much more likely to develop symptoms. About 20% of women develop trichomoniasis of the vagina (trichomonas vaginitis) during their reproductive years (see Trichomonas Vaginitis).

Many people with trichomoniasis also have gonorrhea or other STDs.


In women, the infection usually starts with a greenish yellow, frothy, fishy-smelling discharge from the vagina. In some women, the discharge is slight. The genital area may be irritated and sore, and sexual intercourse may be painful. In severe cases, the genital area and surrounding skin may be inflamed, and the tissues around the vagina's opening (labia) may be swollen. Urination may be painful or frequent, as occurs in a bladder infection. Urinary and vaginal symptoms may occur alone or together.

Most men with trichomoniasis of the urethra have no or only mild symptoms, but they can still infect their sex partners. Some men have a frothy discharge from the penis, pain during urination, and an urge to urinate frequently.

Did You Know...

  • About 1 of 5 women develop trichomoniasis of the vagina.

  • Most men with trichomoniasis have no symptoms, but they can still infect their sex partners.


  • Examination and sometimes culture of a sample of discharge

Doctors suspect trichomoniasis in women with vaginal infections, in men with urethral infections, and in their sex partners.

The organism is much more difficult to detect in men than in women. In women, the diagnosis can usually be made quickly by examining a sample of the vaginal discharge with a microscope and identifying the organism. If results are unclear, the sample is cultured for several days. In men, a sample of the discharge from the end of the penis (obtained in the morning, before urination) may be examined under a microscope and sent to the laboratory for culture. Alternatively, doctors sometimes do tests to identify the genetic material of the organism.

Occasionally, microscopic examination of the urine detects Trichomonas, but identification is more likely if a urine culture is done.

Tests for other STDs are usually also done because many people with trichomoniasis also have gonorrhea or a chlamydial infection.


  • The antibiotic metronidazole or tinidazole

  • Simultaneous treatment of sex partners

A single dose of metronidazole or tinidazole (which are antibiotics), taken by mouth, cures up to 95% of infected women. However, their sex partners must be treated simultaneously or women may be reinfected. Sometimes, if a woman's partner is unlikely to return for follow-up, the woman is given drugs or a prescription to deliver to her sex partner.

Whether single-dose treatment is effective in men is unclear. But men are usually cured after taking the antibiotic for 5 to 7 days.

If taken with alcohol, metronidazole may cause nausea and flushing of the skin. The drug may also cause a metallic taste in the mouth, nausea, or a decrease in the number of white blood cells. Women who take the drug may be more susceptible to vaginal yeast infections (vaginal candidiasis). Metronidazole is best avoided during pregnancy, at least during the first 3 months.

Infected people should abstain from sexual intercourse until the infection is cured, or they can infect their partners.

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