Trichomoniasis: From Symptoms to Treatment and Partner Care

A patient attends a sexual health clinic because her vaginal discharge has changed. It is more noticeable than usual, she has vulval irritation, and passing urine has started to sting. She assumes it is thrush. During the history, however, she mentions a new sexual partner.

There are several possible explanations for these symptoms, and the appearance of vaginal discharge alone cannot tell us which one is responsible. One possibility is trichomoniasis, a sexually transmitted infection caused by Trichomonas vaginalis, a single-celled protozoan parasite that infects the urogenital tract.

Understanding how the organism behaves in the urogenital tract helps explain why some patients develop inflammation and altered discharge while others have few or no symptoms.

What might be causing these symptoms?

Trichomonas vaginalis is a single-celled eukaryotic organism. It exists as a motile trophozoite and has flagella that help it move. Unlike some other protozoa, it does not have a resistant cyst stage. Humans are its only known host and it survives poorly outside the body, so transmission occurs predominantly through sexual contact.

In people with a vagina, infection most often involves the vagina and urethra and may also involve the cervix. In people with a penis, the urethra is the principal site, although the organism can also be found in sites such as the prostate. Many infections produce few or no symptoms, particularly in people with a penis. Someone can therefore transmit T. vaginalis without knowing that infection is present.

When symptoms do occur, vaginal infection can cause increased or altered discharge, vulval soreness, itching, dysuria and discomfort during sex. A yellow-green or frothy discharge is a classic teaching association, as is the punctate cervical erythema sometimes called a “strawberry cervix”. Neither finding is present reliably enough to diagnose trichomoniasis by appearance alone.

What is happening in the genital tract?

Once T. vaginalis reaches the urogenital tract, trophozoites adhere to epithelial cells rather than simply sitting harmlessly in vaginal fluid. Their interaction with the epithelial surface, together with parasite products and the host immune response, produces local inflammation and epithelial injury.

This is where the symptoms begin to make physiological sense. Inflammatory change can make the vulval and vaginal tissues erythematous, sore and more sensitive. Increased inflammatory cells and altered secretions contribute to the change in discharge. Involvement of the urethra can produce dysuria and urethral irritation.

The vaginal environment also changes. A healthy reproductive-age vagina is normally acidic, largely because lactobacilli help maintain a low pH. With trichomoniasis, vaginal pH is often raised. That finding can support clinical suspicion, but it is not specific to T. vaginalis, so it cannot confirm the diagnosis.

The intensity of inflammation varies considerably. This explains an important clinical point: infection does not require the dramatic discharge sometimes shown in textbooks. A patient may have mild symptoms, intermittent symptoms or none at all. Absence of the “classic” presentation should therefore never be used to rule it out.

What else would you want to know?

Once an STI is part of the differential, the history needs to move beyond the discharge itself. Ask when symptoms began and about irritation, dysuria, pelvic or lower abdominal pain, bleeding, dyspareunia and any systemic symptoms. Pregnancy or the possibility of pregnancy is relevant to treatment and wider care.

A sensitive sexual history helps establish exposure and testing needs. This includes recent and current partners, new partners, condom use, the type of sexual contact, previous STIs and whether a partner has symptoms or a known infection. The purpose is not to identify who “caused” an infection. It is to understand which anatomical sites may have been exposed, which tests are appropriate and who may require assessment and treatment.

Pelvic pain, fever, significant bleeding, severe pain or a patient who appears systemically unwell should widen the assessment rather than being attributed automatically to uncomplicated trichomoniasis.

How is trichomoniasis diagnosed?

Laboratory testing is needed because the symptoms overlap with other genital infections. BASHH recommends testing for coexisting sexually transmitted infections in anyone diagnosed with T. vaginalis.

Wet-mount microscopy provides one of the most memorable links between the organism and the laboratory. A fresh sample of vaginal discharge is examined for the characteristic moving trophozoites. The preparation needs to be examined promptly because the organisms lose motility after collection. BASHH notes that microscopy has high specificity in trained hands but relatively limited sensitivity, so a negative wet mount does not reliably exclude infection.

Nucleic acid amplification tests (NAATs) detect genetic material from T. vaginalis rather than relying on seeing a living, moving organism. BASHH identifies molecular testing as the most sensitive approach and recommends it where resources allow. Vaginal swabs are suitable specimens and self-taken vaginal swabs can perform comparably to clinician-taken samples when NAAT is used.

Availability is not identical across UK services. For example, the 2025 Sandyford pathway in NHS Greater Glasgow and Clyde continues to describe local microscopy and culture-based pathways. For a student nurse, the practical lesson is to understand the principle of each test while following the diagnostic pathway used by the local sexual health service.

How is it treated, and why do partners need treatment too?

T. vaginalis is treated with a systemic nitroimidazole. Current BASHH guidance recommends metronidazole 400–500 mg twice daily for seven days, with 500 mg twice daily preferred where that tablet strength is available. A single 2 g oral dose is listed as an alternative, but multidose treatment has better evidence for treatment success. Prescribing must still follow current guidance, individual circumstances and local medicines policy.

Systemic treatment is necessary because infection is not confined to the vaginal surface. The urethra and periurethral or perivaginal glands may also be involved, which is one reason intravaginal metronidazole alone is inadequate treatment.

Treating only the person sitting in front of you leaves an obvious route for the infection to return. BASHH recommends that current partners and partners within the four weeks before presentation are offered full STI screening, including HIV testing, and treated for trichomoniasis irrespective of their investigation result. Partner notification should therefore be discussed as part of treatment, not added as an afterthought.

Patients should avoid sexual intercourse for at least one week and until they and their partner or partners have completed treatment and follow-up. BASHH also advises avoiding alcohol during metronidazole treatment and for 48 hours after the final dose.

If symptoms persist or recur, reassessment is more useful than assuming that the organism is resistant. Reinfection from an untreated partner and adherence should be considered first. BASHH recommends a test of cure when symptoms persist or recur rather than routinely after successful treatment; where NAAT is used for this purpose, the optimum timing is four weeks after treatment was started.

Pregnancy, HIV and the wider clinical picture

Trichomoniasis during pregnancy is associated with adverse pregnancy outcomes including preterm birth and low birthweight, although treating the infection has not been shown clearly to prevent those outcomes. BASHH recommends treating symptomatic infection at diagnosis and states that metronidazole can be used during pregnancy. In pregnancy, the seven-day lower-dose regimen is preferred and high single-dose regimens are not recommended.

There is also an association between trichomoniasis and HIV acquisition and transmission. This does not mean that T. vaginalis causes HIV. Genital inflammation and disruption of the mucosal environment can make HIV transmission biologically easier if exposure occurs. This reinforces the reason a diagnosis of trichomoniasis should lead to a broader sexual-health assessment rather than being managed as an isolated cause of discharge.

Previous infection does not provide reliable protective immunity. A patient can acquire T. vaginalis again after successful treatment, particularly if a partner remains untreated or there is a new exposure.

Back to the patient

For the patient who arrived thinking she had thrush, the most useful nursing response is not to recognise one particular colour of discharge. It is to recognise that discharge, irritation and dysuria have overlapping causes and that a new sexual exposure changes the clinical picture.

Good care means asking about symptoms without assumptions, taking a respectful sexual history, recognising features that require wider assessment, obtaining the appropriate samples and explaining what the tests are looking for. Once trichomoniasis is diagnosed, treatment of partners, testing for other STIs and clear advice about sex during treatment are part of treating the infection itself.

That approach also avoids stigma. An asymptomatic infection may have been present for some time, so a positive result cannot by itself establish when infection was acquired or which partner transmitted it. Clear, neutral explanations can make a difficult consultation considerably easier for the patient.

References

British Association for Sexual Health and HIV (BASHH) (2021) United Kingdom national guideline on the management of Trichomonas vaginalis 2021. Available at: BASHH Trichomonas vaginalis guideline.

British Association for Sexual Health and HIV (BASHH) (2022) Trichomonas Vaginalis (TV): Patient Information. Available at: BASHH patient information.

NHS (2026) Trichomoniasis. Available at: NHS trichomoniasis information.

NHS Greater Glasgow and Clyde, Sandyford (2025) Trichomoniasis: Diagnosis. Available at: Sandyford clinical guideline.