Background: Trichomoniasis is a sexually transmitted protozoal infection caused by Trichomonas vaginalis. Women may be an asymptomatic carrier or experience a range of symptoms up to a mild fulminant inflammatory disease. Its widespread prevalence in the US and international populations creates an important public health concern.

Pathophysiology: T vaginalis inhabits the vaginal and urethral tissues. In women, T vaginalis is isolated from the vagina, cervix, urethra, bladder, and Bartholin and Skene glands. In men, the organism is isolated from the anterior urethra, external genitalia, prostate, epididymis, and semen. Symptoms typically occur after an incubation period of 4?8 days. The protozoan pathogen causes direct damage to the epithelium, leading to microulcerations.


  • In the US: Trichomoniasis affects 2-3 million women annually. The organism also is detected in 30-40% of men who are exposed. The prevalence of T vaginalis infection at clinics treating sexually transmitted diseases (STDs) varies between 8-31%. In men, trichomoniasis may account for as much as 17% of nongonococcal, non-chlamydial urethritis.
  • Internationally: Trichomoniasis affects approximately 180 million women worldwide. The frequency in Europe is similar to the US. In Africa, the prevalence may be much higher. Trichomoniasis was present in 65% of pregnant women attending an antenatal clinic in South Africa.


  • Pregnant women infected with T vaginalis are 30% more likely than uninfected women to deliver preterm or to have a low birth weight infant. They are also 40% more likely to deliver a preterm, low birthweight infant.
  • Complications in men include prostatitis, epididymitis, urethral stricture disease, and infertility.
  • T vaginalis infection is highly associated with the presence of other STDs, such as gonorrhea, chlamydia, and HIV. Coexisting symptomatic trichomoniasis in men with HIV have a 6-fold increase in concentration of HIV in their semen. Theoretically, this confers an increased risk of transmission to their sexual partners.


  • Symptomatic trichomoniasis more commonly occurs in women.
  • Trichomoniasis infection in men is less clinically apparent. 10-50% of the infected men may be asymptomatic carriers.


  • Trichomoniasis is a STD; therefore, it is encountered in sexually active adolescents and adults.




  • Women
    • Symptoms range from none in asymptomatic carriers to a severe pelvic inflammatory disease.
    • Common symptoms are yellow vaginal discharge, abnormal vaginal odor, dyspareunia, and vulvar itching.
    • Some may experience dysuria.
  • Men
    • Symptoms range from none in asymptomatic carriers to urethritis complicated by prostatitis.
    • The usual incubation period for the development of symptomatic disease is 10 days or less.
    • Nongonococcal urethritis is the most typical clinical syndrome in symptomatic men.
    • Discharge is present in 33-50% of symptomatic men and varies from purulent to mucoid in character.
    • Most symptomatic infections are intermittent and self-limiting.


  • Women
    • Purulent or homogenous vaginal discharge, and vulvar or vaginal erythema are common.
    • The finding of colpitis macularis, or strawberry cervix, describes a diffuse or patchy macular erythematous lesion of the cervix. This is a specific sign for trichomoniasis, but visible only 1-2% of the time without the aid of colposcopy. With colposcopy, colpitis macularis is detected in up to 45% of the cases.
    • Lower abdominal tenderness may be present; however, this is described in less than 10% of the patients. If this occurs, the possibility of a coexisting salpingitis or an intra-abdominal pathology is evident.
    • Coexisting infections with Neisseria gonorrhea, candidiasis, and bacterial vaginosis are common and may produce a mixed clinical picture.
  • Men
    • The physical examination is generally unremarkable unless the infection is complicated. It may be associated with local inflammatory states, including balanitis and balanoposthitis.
    • Physical findings of epididymitis and prostatitis also may occur.



Bacterial vaginosis
Atrophic vaginitis with secondary infection
Erosive lichen planus
Foreign body vaginosis



Lab Studies:

  • Laboratory studies aid in the demonstration of the T vaginalis organism and to differentiate the infection from other causes of vaginitis.
  • Bedside laboratory studies
    • The vaginal pH measured on Nitrazine paper is elevated.
    • Usually, the pH is above 5.0 and may be as high as 6.0.
    • Bacterial vaginosis or atrophic vaginitis also may cause elevation in the vaginal pH.
    • The potassium hydroxide amine test reveals a fishy odor from the application of 10% potassium hydroxide to a vaginal swab sample, which suggests trichomoniasis and bacterial vaginosis.
  • Saline microscopic examination
    • Obtaining a vaginal swab sample for saline wet mount evaluation is an easy, valuable, and economical tool for obtaining diagnosis.
    • Trichomonads, which are ovoid-shaped parasites, are slightly larger than polymorphonuclear lymphocytes (PMNs) and may be identified by their ameboid mobility. Trichomonads cause an inflammatory reaction; therefore, a large number of PMNs usually are present and this number correlates with the severity of the infection.
    • A saline wet prep is positive for identifying trichomonads in approximately 60% of the cases.
  • Papanicolaou smears
    • Trichomonads may be viewed on pap smears, but they only have a sensitivity of 60-70% when compared to the use of saline microscopy.
    • False-positive results are common with this technique.
  • Cultures
    • Incubate the cultures anaerobically.
    • Growth is detected within 48 hours and has a sensitivity of 95%.
    • Culture is important in the diagnosis of men, because the wet prep is often negative.
  • Polymerase chain reaction
    • Polymerase chain reaction (PCR) methods report high sensitivity and specificity (97% and 98%, respectively).
    • The availability of this test may be limited.



Medical Care:

  • Systemic treatment is important to ensure a cure, since trichomoniasis is an infection of multiple sites (eg, vaginal epithelium, Skene glands, Bartholin glands, urethra).
  • Oral metronidazole is the treatment of choice and is shown in multiple studies to be superior in efficacy when compared to intravaginal treatment. Treatment failures may require a high-dose metronidazole regimen.


  • Instruct the patient to avoid alcohol while taking metronidazole, because it may cause a disulfiram-like reaction.



The 5-nitroimidazole group of drugs are antiprotozoal effective agents, which are used for the treatment of trichomoniasis. The mechanism of action is not well understood; however, it is known that anaerobic organisms preferentially reduce the 5-nitro group and active metabolites likely interact with anaerobic bacterial and protozoal DNA.

Drug Category: Antiprotozoal agents -- Therapy must be comprehensive and should cover all likely pathogens in the context of this clinical setting.

Drug Name

Metronidazole (Flagyl) -- This medication is available PO, IV, and as intravaginal suppository gel. Highly effective in the treatment of many anaerobic bacterial and protozoal infections.

Adult Dose

250 mg PO tid qwk or 2 g PO one time dose

Pediatric Dose

15 mg/kg/d divided tid qwk


Documented hypersensitivity to the 5-nitroimidazole class of medications


Inhibits metabolism of warfarin and potentiates the anticoagulant effect; causes an intolerance to alcohol similar to disulfiram; abdominal cramps, nausea, vomiting, headaches, and flushing when co-ingested with alcohol; cimetidine prolongs the plasma clearance by inhibiting metabolic enzymes; conversely, drugs that induce liver enzymes (eg, phenobarbital) may increase the elimination of metronidazole


B - Usually safe but benefits must outweigh the risks.


Usually well tolerated; commonly encountered side effects are nausea, vomiting, anorexia, and a metallic taste in the mouth; most serious side effects involve the nervous system and are manifested as convulsions and peripheral neuropathy, which are rare unless large doses are given for a prolonged period of time; drug is slowly impaired in patients with reduced hepatic function; reduce dose in patients with reduced hepatic function to prevent toxic levels from building in the plasma




Further Outpatient Care:

  • Sexual partners must be treated to prevent reinfection.
  • Consider empiric treatment of other STDs that frequently coexist with trichomoniasis.
  • Advise the patient to avoid intercourse until therapy is complete and the patient and partner are asymptomatic.
  • Persistent treatment failures may require metronidazole susceptibility testing through the Center for Disease Control (CDC).


  • Condoms and oral contraceptives may protect against transmission of trichomoniasis.


  • Please see Morbidity section

Patient Education:

  • Educate the patient about STDs, including HIV, and methods of prevention.
  • Discuss the side effects and interactions encountered with metronidazole.



Medical/Legal Pitfalls:

  • Failure to treat during pregnancy may result in an adverse fetal outcome.
  • Screen for STDs in the pregnant patient and treat appropriately.

Special Concerns:

  • The use of metronidazole in the first trimester of pregnancy is traditionally avoided because of concern over possible teratogenic risk. Several studies, including a large meta-analysis of pregnant women exposed to metronidazole in the first trimester, found no increased risk of birth defects. Consider this when weighing the benefits and any possible risk in treating pregnant patients.



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Medicine is a constantly changing science and not all therapies are clearly established. New research changes drug and treatment therapies daily. The authors, editors, and publisher of this journal have used their best efforts to provide information that is up-to-date and accurate and is generally accepted within medical standards at the time of publication. However, as medical science is constantly changing and human error is always possible, the authors, editors, and publisher or any other party involved with the publication of this article do not warrant the information in this article is accurate or complete, nor are they responsible for omissions or errors in the article or for the results of using this information. The reader should confirm the information in this article from other sources prior to use. In particular, all drug doses, indications, and contraindications should be confirmed in the package insert. FULL DISCLAIMER