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Author: Marie Hartley, Staff Writer, 2009. Updated by Dr Natalie Renaud, Registrar, and Dr Susan Bray, Sexual Health Physician, Sexual Health Clinic, Hamilton, New Zealand. DermNet NZ Editor in Chief: Adjunct Assoc. Prof. Amanda Oakley, Dermatologist, Hamilton, New Zealand. Copy edited by Gus Mitchell. 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. Infections of the cervix, bladder, prostate, and Bartholin glands are less frequent.
The table below describes the clinical features of trichomoniasis in men and in women.
|Duration of infection||
Asymptomatic carriers for months or years.
Spontaneous resolution can occur.
|Trichomoniasis infection is often short-lived (up to 10 days) but can persist for months.|
|Signs and symptoms||
A purulent thin malodorous vaginal discharge is common.
A yellowish-green frothy foul-smelling discharge occurs in 10–30%.
Signs may include vulval erythema, vaginal discharge, elevated vaginal pH (> 4.5), or punctate bleeding of the cervix (strawberry cervix/colpitis macularis) or vagina.
Urethritis resulting in irritation inside the penis, scant, thin discharge, or slight burning after urination or ejaculation.
Trichomoniasis accounts for up to 11% of cases of non-gonococcal urethritis.
Symptoms usually disappear within a few weeks without treatment.
Trichomoniasis facilitates the acquisition and transmission of human immune deficiency virus (HIV).
It is associated with an increased risk of post-hysterectomy infection, tubal infertility, and cervical cancer.
In pregnancy, it is associated with low birth weight, premature rupture of membranes, and preterm delivery.
|Trichomoniasis facilitates acquisition and transmission of HIV, infection of the prostate, foreskin and epididymis, and decreased sperm motility.|
In a newborn, trichomoniasis can cause fever, breathing problems, urinary tract infection, and vaginal discharge.
Spontaneous resolution of infection occurs as oestrogen level drops.
A ‘strawberry cervix’, seen in 2% of women with trichomoniasis, strongly indicates the 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 available culture system (the pouch kit) has a sensitivity of 80% and the results are available in 3–5 days. The less available culture system (on Diamond medium) has a sensitivity and specificity of > 95% and the results are available in 7 days.
Rapid antigen and DNA hybridisation test is a commercially available point of care test for trichomoniasis.
A cervical smear test (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 in pregnancy and lactation. Tinidazole or ornidazole are alternatives for males, non-pregnant and non-lactating females.
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%.
Like other sexually transmitted infections, 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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