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Author: Marie Hartley, Staff Writer, 2009. Updated by Dr Natalie Renaud, Registrar, and Dr Susan Bray, Sexual Health Physician, Hamilton, Sexual Health Clinic, Hamilton, New Zealand. DermNet NZ Editor in Chief: Adjunct A/Prof. Amanda Oakley, Dermatologist, Hamilton, New Zealand. Copy edited by Gus Mitchell/Maria McGivern. September 2019.
Trichomoniasis is a sexually transmitted infection (STI) caused by the protozoan parasite, Trichomonas vaginalis (T. vaginalis).
Trichomoniasis is the most common non-viral sexually transmitted infection worldwide. A woman can acquire trichomoniasis from an infected man or woman, but a man usually acquires it from an infected woman. Vertical transmission from mother to child can also occur.
Trichomoniasis is much more common in women than in men. In the United States:
Small studies in New Zealand suggest a prevalence of 2.2% in females of reproductive age.
The incubation period of trichomoniasis is estimated to be between 4 and 28 days. T. vaginalis usually infects the vagina, urethra, and paraurethral glands (mucus-producing glands on the distal female urethra). Infections of the cervix, bladder, prostate, and Bartholin glands (compound alveolar gland on each side of the vagina) are less frequent.
The table below describes the clinical features of trichomoniasis in men and in women.
|Duration of infection||
|Signs and symptoms||
A ‘strawberry cervix’, which is seen in 2% of women with trichomoniasis, strongly indicates this diagnosis whereas the other clinical features are not specific to T. vaginalis infection. The vaginal pH is usually > 4.5.
The primary methods for the diagnosis of trichomoniasis are as follows.
A wet mount involves placing a small amount of vaginal discharge on a slide with a few drops of saline.
Culture requires a urethral swab in men or a high vaginal swab in women. It is harder to grow T. vaginalis from men than women, and false negatives are common. The reliability of culture may be improved by combining a urethral swab with a urine sample.
The more widely available culture system (the InPouch® kit) has a sensitivity of 80% and the results are available in 3–5 days. The less widely available culture system (Diamond's medium) has a sensitivity and specificity of > 95% and the results are available in 7 days.
The rapid antigen and DNA hybridisation test is a commercially available point-of-care test for trichomoniasis.
A cervical smear test (whether liquid-based cytology or conventional pap smear) cannot be used as a screening test for trichomoniasis. When the presence of trichomonas is noted on a smear test result, a confirmatory test with culture or NAAT should be performed.
Conventional pap smears have more false positives than liquid-based cytology, but liquid-based cytology has higher specificity.
The oral antibiotic, metronidazole, is prescribed for trichomoniasis and is safe for use during pregnancy and lactation. Tinidazole or ornidazole are alternatives for men and non-pregnant and non-lactating women.
Resistance to metronidazole and other nitroimidazoles have been reported in up to 5% of clinical isolates of T. vaginalis.
Nitroimidazoles have a > 90% cure rate, intravaginal preparations result in a 50% cure rate, and there is spontaneous resolution in 20–25% of cases of trichomoniasis.
Like other STIs, the risk of acquiring trichomoniasis is reduced by safe-sex practices, including limiting the number of sexual partners, using condoms, and avoiding re-infection by not having sexual contact with untreated sexual partners.
If you think you are infected, stop any sexual contact and see your usual doctor or a specialist clinician at a sexual health clinic.
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