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"Trich" redirects here. For the hair-pulling disorder, see Trichotillomania.
Not to be confused with Trichinosis or Trichuriasis.
Trichomonas pap test.jpg
Micrograph showing a positive result for trichomoniasis. A trichomonas organism is seen on the top-right of the image.
Classification and external resources
Specialty Gynecology
ICD-10 A59
ICD-9-CM 131,007.3
DiseasesDB 13334
MedlinePlus 001331
eMedicine med/2308 emerg/613
MeSH D014246

Trichomoniasis is a common cause of vaginitis. It is a sexually transmitted infection, and is caused by the single-celled protozoan parasite Trichomonas vaginalis producing mechanical stress on host cells and then ingesting cell fragments after cell death.[1] Trichomoniasis is primarily an infection of the urogenital tract; the most common site of infection is the urethra and the vagina in women.

Signs and symptoms[edit]

Most people infected with trichomonas vaginalis do not have any symptoms.[2] Symptoms experienced include pain, burning or itching in the penis, urethra (urethritis), or vagina (vaginitis). Discomfort for both sexes may increase during intercourse and urination. For women there may also be a yellow-green, itchy, frothy, foul-smelling ("fishy" smell) vaginal discharge. In rare cases, lower abdominal pain can occur. Symptoms usually appear within 5 to 28 days of exposure.[3]


Lifecycle of Trichomonas

The human genital tract is the only reservoir for this species. Trichomonas is transmitted through sexual or genital contact.[4]

Genetic sequence[edit]

A draft sequence of the Trichomonas genome was published on January 12, 2007 in the journal Science confirming that the genome has at least 26,000 genes, a similar number to the human genome. An additional ~35,000 unconfirmed genes, including thousands that are part of potential transposable elements, brings the gene content to well over 60,000.[5]


There are three main ways to test for Trichomoniasis.

  • The first is known as saline microscopy. This is the most commonly used method and requires an endocervical, vaginal, or penile swab specimen for examination under a microscope. The presence of one or multiple trichomonads constitutes a positive result. This method is cheap but has a low sensitivity (60-70%) often due to an inadequate sample, resulting in false negatives.[6][7]
  • The second diagnostic method is culture, (InPouch TV culture test, BioMed Diagnostics, San Jose, CA) which has historically been the “gold standard” in infectious disease diagnosis. Trichomonas Vaginalis culture tests are relatively cheap; however, sensitivity is still somewhat low (70-89%).[8]
  • The third method includes the nucleic acid amplification tests (NAATs) which are more sensitive. These new NAATs include the APTIMA Trichomonas assay (Gen-Probe Inc, San Diego, CA) and the AFFIRM VPIII (BD Diagnostics, Sparks, MD).[8] These tests are more costly than microscopy and culture, and are highly sensitive (80-90%).[9]


Use of male condoms may help prevent the spread of trichomoniasis,[10] although careful studies have never been done that focus on how to prevent this infection. Infection with Trichomoniasis through water is unlikely because Trichomonas vaginalis dies in water after 45–60 minutes, in thermal water after 30 minutes to 3 hours and in diluted urine after 5–6 hours.[11]

Currently there are no routine standard screening requirements for the general U.S. population receiving family planning or STI testing.[12][13] The Centers for Disease Control and Prevention (CDC) recommends Trichomoniasis testing for females with vaginal discharge[14] and can be considered for females at higher risk for infection or of HIV-positive serostatus.[12]

The advent of new, highly specific and sensitive trichomoniasis tests present opportunities for new screening protocols for both men and women.[12][15] Careful planning, discussion, and research are required to determine the cost-efficiency and most beneficial use of these new tests for the diagnosis and treatment of trichomoniasis in the U.S., which can lead to better prevention efforts.[12][15]

A number of strategies have been found to improve follow-up for STI testing including email and text messaging as reminders of appointments.[16]


Treatment for both pregnant and non-pregnant patients usually utilizes metronidazole (Flagyl),[17] 2000 mg by mouth once.[18] Caution should be used in pregnancy, especially in the first trimester.[19] Sexual partners, even if asymptomatic, should also be treated.[11]

For 95-97% of cases, infection is resolved after one dose of metronidazole.[14][20] Studies suggest that 4-5% of trichomonas cases are resistant to metronidazole, which may account for some “repeat” cases.[21][22] Without treatment, trichomoniasis can persist for months to years in women, and is thought to improve without treatment in men.[22] Women living with HIV infection have better cure rates if treated for 7 days rather than with one dose.[23][18]


Evidence from a randomized controlled trials for screening pregnant women who do not have symptoms for infection with trichomoniasis and treating women who test positive for the infection have not consistently shown a reduced risk of preterm birth.[24][25] Further studies are needed to verify this result and determine the best method of screening. In the US, screening of pregnant women without any symptoms is only recommended in those with HIV as trichomonas infection is associated with increased risk of transmitting HIV to the fetus.[18]


Research has shown a link between trichomoniasis and two serious sequelae. Data suggest that:

  • Trichomoniasis is associated with increased risk of transmission and infection of HIV.[22][26]
  • Trichomoniasis may cause a woman to deliver a low-birth-weight or premature infant.[22]
  • The role of trichomonas infection in causing cervical cancer is unclear, although trichomonas infection may be associated with co-infection with high-risk strains of HPV.[27]
  • T. vaginalis infection in males has been found to cause asymptomatic urethritis and prostatitis. In the prostate, it may create chronic inflammation that may eventually lead to prostate cancer.[28][29]


Trichomonas vaginalis infection is the most common non-viral STI in the world with an estimated 248 million new cases per year.[30][31] It is more common in women (2.7%) than males (1.4%).[32] It is also the most common non-viral STI in the U.S., with an estimated 3.7 million prevalent cases and 1.1 million new cases per year.[33][34] Recent studies have posited prevalence to be 3% of the general U.S. population,[9][35] and 7.5-32% of moderate-to-high risk (including incarcerated) populations.[36][37][38][39][40][41][42][43]


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External links[edit]