Trichomoniasis1 is a common sexually transmitted vaginal infection. A synonym for trichomoniasis is trich.


In the USA, 3.7 million people may be infected but only 30% of them develop symptoms.2 The classic malodorous discharge that is worse after intercourse occurs in only 10% of affected patients.

Of infected women, 80% have partners with the Trichomonas organism. It commonly occurs at 20 to 29 years of age.


Caused by Trichomonas vaginalis, a unicellular flagellate protozoan, the infection can be transmitted penis to vagina and vice versa or vagina to vagina. It may also be found in the mouth and anus and in the urine.

Symptoms and clinical features

70% of people are asymptomatic. The rest may have mild to moderate vulvar irritation and inflammation. The infection causes a smelly discharge leading to secondary vulvar burning and itching. Pruritus and some degree of dyspareunia are seen in 25% to 50% of the patients. Urinary symptoms, dysuria, and frequency sometimes occur. Rarely, there is lower abdominal pain.

A diffusely red vestibule with an abundant, frothy, homogeneous, greenish or yellowish discharge, which is malodorous, is observed. The cervix may also be inflamed and friable, dotted with multiple darker red macules and papules.

Pathology/Laboratory Findings

Identification of the organism on a wet mount of the vaginal secretion with an associated high pH (above 5) leads to a diagnosis. On a smear of this secretion, multiple white cells, epithelial cells, absent lactobacilli, and the typical tear-drop shaped, motile protozoan with its five small flagella are observed. The jerky movements of these protists are easy to recognize as they move across the slide. The addition of KOH to a wet smear gives a typical “fishy” odor, referred to as the positive “whiff” test. The organism can be cultured or identified by DNA probe.


Identification of the organism on a wet mount of the vaginal secretion leads to a diagnosis. In the case of elevated vaginal pH and sheets of WBCs on wet mount but no visible organisms, culture or Affirm is advised. Performing a wet prep with a cooled specimen may render the organisms motionless and difficult to identify. Less commonly, there may be only one organism on review of the entire slide, making it easy to miss.

Differential diagnosis

Differential diagnoses include moniliasis, bacterial vaginosis, gonorrhea, desquamative inflammatory vaginitis, vaginal atrophy, and a foreign body.


Treatments are in order of preference. Treat all sexual partners.

  • Metronidazole (Flagyl) 2 g orally as a single dose or 1 g twice in 1 day (with no alcohol)
  • Alternate regimens include:
    Metronidazole (Flagyl) 500 mg orally twice a day x 7 days (with no alcohol)
    Metronidazole (Flagyl) 250 mg orally three times a day x 7 days (with no alcohol)
    Tinidazole 2 g orally as a single dose.

See the CDC guidelines for the most up to date information on Trichomoniasis.


  1. Fisher BK, Margesson, LJ. Genital Skin Disorders: Diagnosis and Treatment. Mosby, Inc., 1998. 152-153.
  2. Sutton M, Sternberg M, Koumans EH, McQuillan G, Berman S, Markowitz L. The prevalence of Trichomonas vaginalis infection among reproductive-age women in the United States, 2001-2004. Clin Infect Dis. 2007 Nov 15;45(10):1319-26.