Trichomoniasis

What is trichomoniasis?

Trichomoniasis is a sexually transmitted infection (STI) caused by the protozoan parasite, Trichomonas vaginalis (T. vaginalis).

Who gets trichomoniasis?

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:

• The reported prevalence of asymptomatic infection in women is 1.3–13.3%
• The prevalence of trichomoniasis is much higher in non-white populations than in white populations
• A prevalence of 5–29% has been reported in women with symptoms, who have another STI, or who are from a high-risk setting (eg, a correctional facility)
• A higher prevalence is reported when nucleic acid amplification tests (NAATs) are used compared to other diagnostic methods
• Trichomonas infections are most common in women aged 21–22 years and in women aged 48–51 years
• An overall trichomoniasis prevalence of 3.7% has been reported in men, with a peak prevalence of 5.7% in men aged 40–49 years
• T. vaginalis is detected in 30–70% of the male partners of infected women.

Small studies in New Zealand suggest a prevalence of 2.2% in females of reproductive age.

What are the clinical features of trichomoniasis?

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.

Table. Clinical features of trichomoniasis

What clinical signs are seen in trichomoniasis?

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.

How is trichomoniasis diagnosed?

The primary methods for the diagnosis of trichomoniasis are as follows.

Wet mount microscopy and staining

A wet mount involves placing a small amount of vaginal discharge on a slide with a few drops of saline.

• It is immediately examined under a microscope.
• The motile trichomonads (T. vaginalis protozoans) are visible for about 10–20 minutes after sample collection.
• Excess white blood cells may also be seen and indicate accompanying inflammation.
• Microscopy can detect up to 60–70% of cases of trichomoniasis when compared to culture.
• Staining of dead organisms with acridine orange has higher sensitivity but is not widely available.

Culture of Trichomonas vaginalis

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.

Nucleic acid amplification test

• An NAAT detects T. vaginalis RNA in a urine sample or a vaginal swab.
• Some brands only detect T. vaginalis, whereas others combine testing for Neisseria gonorrhoea and Chlamydia trachomatis.
• NAATs have a sensitivity and specificity of 95–100%.

Rapid antigen and DNA hybridisation test

The rapid antigen and DNA hybridisation test is a commercially available point-of-care test for trichomoniasis.

• The results are available within 1 hour.
• It has variable sensitivity and specificity.
• It has the potential for use in high prevalence, geographically isolated populations.

Cervical smear tests

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.

What is the treatment of trichomoniasis?

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.

• Both male and female sexual partners require treatment to prevent re-infection; partners should be treated even if they have no symptoms and irrespective of the test result, in particular, if cultures are being used in men.
• Patients should avoid sex until they and their sexual partners have completed treatment and have no symptoms (usually about 1 week).
• A full STI screen is recommended due to the increased likelihood of co-infection with other STIs.

Resistance to metronidazole and other nitroimidazoles have been reported in up to 5% of clinical isolates of T. vaginalis.

• Higher doses of the above drugs are usually tried first.
• If this is not successful, topical (intravaginal) medications used include paromomycin, furazolidone, acetarsol, and nonoxynol-9.

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.

How is trichomoniasis prevented?

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.