What is trichomonas?

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Trichomonas is a common sexually transmitted disease (STD), or infection. It is a symptomatic infection of the vaginal tract in women and a usually asymptomatic infection of the urethra in men.
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Trichomonas is a common sexually transmitted disease (STD), or infection. It is a symptomatic infection of the vaginal tract in women and a usually asymptomatic infection of the urethra in men.


Trichomonas is caused by infection with the single-celled protozoan parasite Trichomonas vaginalis, which is transmitted almost exclusively through vaginal sexual intercourse. Extremely rare cases of fomite transmission, that is, transmission through a contaminated object, have been reported.

Risk Factors

Risk factors for contacting trichomonas include those things that increase the chances of contact with an infected partner. Persons with multiple sexual partners, who have unprotected sexual intercourse, and who have untreated sexual partners are at high risk.

In addition to the noted risk factors for trichomonas, associated high risks have received focused attention from researchers. Increased rates of human immunodeficiency virus (HIV) infection have been documented in women with a history of trichomonas. Biological changes associated with trichomonas may occur. Microabrasions caused by the inflammatory response associated with the organism, and possibly with itching and scratching from the discomfort caused by the infection, can make trichomonas-infected women more susceptible to seroconversion with HIV if they are exposed to infectious fluids. Pregnant women infected with T. vaginalis have demonstrated increased rates of complications, including premature rupture of membranes, preterm birth, and delivery of low-birth-weight neonates.


In women, trichomonas symptoms include a foamy grayish discharge with a foul odor; mild, moderate, or intense itching and burning that often includes pain with intercourse; and, in severe cases, erythema (redness) of the vagina and inner vulvar folds. Some women may experience pain with urination and may confuse their symptoms with that of a urinary tract infection.

Men are usually asymptomatic, but men who do have symptoms present with penile burning on urination, a reddened urethral opening, and a clear penile discharge that is often misdiagnosed as nongonococcal urethritis or chlamydia. This misdiagnosis can result in the provision of antibiotics that are effective against chlamydia but that have no treatment value for trichomonas. Men with longstanding infection may also have symptoms of prostatitis.

Symptoms may present anywhere from a few days to a month following transmission, so for persons with multiple partners, there is often no way to determine when the infection was acquired based on symptoms.

Screening and Diagnosis

Trichomonas is one of the STDs for which screening tests are not widely employed. Infection in women is marked by an increased pH (acidity) of the vaginal fluid in most cases, so screening women who are undergoing vaginal speculum examinations with pH paper has been suggested.

For many years the gold standard for diagnosis has been the saline wet prep, which requires a working microscope, skill in examining wet prep specimens, and a laboratory certification for the clinical setting for provider-performed microscopy. The sensitivity (the percentage of time a positive result is identified from the testing) of vaginal wet preps for trichomonas is estimated to be between 60 and 70 percent, but the specificity is very high if only mobile trichomonads are used for identification. Specificity refers to a lack of false-positive results and is especially important for a sexually transmitted infection that can raise serious issues in a relationship. Sensitivity is increased by scanning multiple fields and by examination immediately after collection of a specimen, because the organisms may die quickly. Because of these limitations, many clinical settings have not always been able to offer wet prep testing, and laboratory diagnostic testing methodologies have become available with send-out and point-of-care testing.

Many issues remain concerning the low specificity of these DNA (deoxyribonucleic acid) probe or PCR-based tests. Commercial tests continue to enter the market. Pap screening may also produce incidental findings of trichomonal organisms, but because of a high rate of false-positive results (low specificity), this should only be treated as a screening, rather than a diagnostic finding, so confirmatory testing is required. Culture is also available in a few specialty laboratory settings, utilizing vaginal secretions in women and urine, urethral swabs, or semen in men. In laboratories that have the capability of centrifuging urine and doing a microscopic examination of the spun sediment, trichomonal organisms, or trichomonads may be identified in male urine sediment.

Diagnosis is usually made from testing symptomatic women through a wet prep of vaginal discharge. Male partners receive a presumptive diagnosis.

Treatment and Therapy

Trichomonas is a curable sexually transmitted infection, without a high rate of relapse if partners are properly treated and if future behavioral changes can be implemented. Treatment is generally with only two approved medications: metronidazole in a single 2 gram (g) oral dose, or tinidazole in a single 2 g oral dose. Alternatively, metronidazole can be given as one 500 milligram tablet twice each day for seven days.

Persons who are treated with a one-dose regimen are given multiple tablets (often four). They need to remain abstinent for one week while the medication is eradicating the organism. They also need to abstain from alcohol for twenty-four hours before taking the medications and for twenty-four hours after completing metronidazole and for seventy-two hours after completing tinidazole, as severe symptoms can result from interaction with alcohol. If a provider has concerns about resistant infection, he or she can contact the Centers for Disease Control and Prevention. Metronidazole is safe to give during pregnancy and is preferred over tinidazole.

Prevention and Outcomes

Prevention of infection with T. vaginalis involves decreasing one’s number of sexual partners, practicing mutual monogamy, and using barrier protection such as male or female condoms. Prevention is also accomplished at the community level through the contact and treatment of all potentially infected partners.


Boston Women’s Health Collective. Our Bodies, Ourselves: A New Edition for a New Era. 35th anniversary ed. New York: Simon & Schuster, 2005. A popular, classic book dealing with all aspects of women’s sexuality, including sexually transmitted infections and safer sex.

Grimshaw-Mulcahy, Laura J. “Now I Know My STDs: Part II—Bacterial and Protozoal.” Journal for Nurse Practitioners 4 (2008): 271-281. A review article that has a comprehensive section on trichomonas.

Holmes, King K., et al., eds. Sexually Transmitted Diseases. 4th ed. New York: McGraw-Hill Medical, 2008. A comprehensive text covering all aspects of sexually transmitted infections and diseases.

Johnston, Victoria J., and David C. Mabey. “Global Epidemiology and Control of Trichomonas Vaginalis.” Current Opinion in Infectious Diseases 21 (2008): 56-64. Updated information on epidemiology and treatment trends.

Szumigala, J. A., et al. “Vulvovaginitis: Trichomonas.” In Ferri’s Clinical Advisor 2011: Instant Diagnosis and Treatment, edited by Fred F. Ferri. Philadelphia: Mosby/Elsevier, 2011. Provides recommendations on clinical treatments for trichomonas infection.

Van Der Pol, Barbara, et al. “Trichomonas Vaginalis Infection and Human Immunodeficiency Virus Acquisition in African Women.” Journal of Infectious Diseases 197 (2008): 548-555. Research article on the risks that trichomonas can pose for increased seroconversion to HIV.