Trichomoniasis

Overview

Trichomoniasis is caused by the flagellated protozoan Trichomonas vaginalis. It infects the lower genital tract in women and the urethra or prostate region in men. The organism is transmitted primarily through sexual contact. A large proportion of infections are asymptomatic, so transmission can continue without either partner recognizing an infection. ^{[1] [2]}

The parasite adheres to urogenital epithelium and causes local inflammation. In women, inflammation can produce diffuse vaginal erythema, discharge and irritation; in men, urethral infection is often mild or asymptomatic. The infection does not usually invade deep tissue, but it is associated with increased genital inflammation and can interact with HIV transmission risk. ^{[1] [2]}

Trichomoniasis is clinically important because symptoms are nonspecific and reinfection is frequent. Treating only the symptomatic patient without partner management can result in a new positive test soon afterward. In women, bacterial vaginosis and other STIs commonly coexist, so a diagnosis is an opportunity to assess broader sexual-health risks. ^{[1] [2] [3]}

Symptoms and warning signs

Women may develop diffuse malodorous yellow-green or frothy discharge, vulvar irritation, burning, painful urination or discomfort during sex. Men can have urethral discharge, irritation or burning after urination or ejaculation, but many have no symptoms. Symptoms can come and go, so intermittent improvement does not mean the infection has cleared. ^{[1] [2]}

Trichomoniasis itself rarely causes an emergency, but severe pelvic pain, fever, pregnancy with significant pain or bleeding, testicular swelling or symptoms of another invasive STI require prompt medical assessment. People with HIV or significant pregnancy complications should receive coordinated clinician-led care rather than self-treatment. ^{[1] [2]}

Diagnosis

Laboratory testing is recommended because clinical appearance alone is unreliable. Nucleic acid amplification tests are highly sensitive and available for several specimen types. Point-of-care antigen or molecular tests may also be used. Wet-mount microscopy can show motile organisms but has lower sensitivity, especially when the sample is not examined immediately. ^{[1] [2]}

Testing should be considered in women presenting with vaginal discharge and in people with known exposure, and screening is recommended in selected higher-risk populations according to local guidance. A positive diagnosis should prompt testing for other STIs, including HIV, syphilis, gonorrhea and chlamydia, according to CDC recommendations and individual risk. ^{[1] [2] [3]}

Bacterial vaginosis, vulvovaginal candidiasis, gonorrhea, chlamydia, cervicitis and noninfectious vaginitis can all cause overlapping symptoms. Vaginal pH and microscopy may provide clues, but molecular testing improves specificity. In men, urethritis from gonorrhea or chlamydia is an important alternative diagnosis. ^{[2] [3]}

Causes, risk factors and clinical context

Risk increases with unprotected sex, new or multiple partners and untreated infected partners. Prior trichomoniasis is a risk for recurrence because exposure networks can persist. The infection is common worldwide and does not imply poor hygiene. Barrier protection reduces but does not eliminate transmission risk. ^{[1] [2]}

Without treatment, infection can persist for months or longer. Symptoms may fluctuate. Reinfection after successful therapy is common, particularly when partners are untreated. Persistent positive tests also require attention to the timing of NAAT because residual nucleic acid can sometimes be detected too soon after treatment. ^{[1] [2] [3]}

Complications and why the diagnosis matters

Trichomoniasis is associated with adverse pregnancy outcomes in observational studies and with increased acquisition or transmission of HIV. It can contribute to persistent genital inflammation. These associations do not mean every infected person will develop complications, but they strengthen the rationale for testing and treatment. ^{[1] [2]}

Recommended nitroimidazole regimens cure most infections. Treatment failure can result from reinfection, nonadherence or antimicrobial resistance. CDC offers susceptibility testing support for selected persistent infections not explained by re-exposure. Long-term prognosis is good when infection and partners are appropriately treated. ^{[1] [2] [3]}

Treatment and management

Oral metronidazole is first-line therapy, with regimen differences by sex and clinical context in CDC guidance. Tinidazole is an alternative. Topical metronidazole gel is not adequate because it does not reach all infected urogenital sites. Sexual partners should be treated at the same time to reduce reinfection. ^{[1] [2]}

Patients are advised to avoid sex until treatment is completed, symptoms have resolved and partners have been treated. Testing for other STIs should be offered. Women are generally advised to be retested after treatment because repeat infection is common. Persistent symptoms warrant repeat evaluation rather than repeated empiric treatment without confirming the cause. ^{[1] [2] [3]}

Nitroimidazoles can interact with medicines and have pregnancy and alcohol-use counseling considerations depending on the specific drug and guideline. Treatment should be prescribed rather than improvised from leftover antibiotics. Vaginal symptoms should not be assumed to be trichomoniasis without testing when testing is available. ^{[1] [2]}

Follow-up, recovery and prevention

CDC recommends retesting sexually active women about three months after treatment regardless of whether they believe partners were treated. Evidence is insufficient for routine retesting of men after successful treatment. For recurrent disease, clinicians assess re-exposure first, then choose repeat testing and treatment based on the prior regimen and resistance risk. ^{[1] [2]}

Consistent condom use reduces transmission risk. Testing and treating both the patient and sexual partners are central to prevention. People should avoid sexual contact until therapy is completed and symptoms have resolved. Routine screening recommendations vary by population and country. ^{[1] [2] [3]}

Special situations and care pathway

Women with HIV have specific treatment and retesting recommendations because trichomoniasis is linked to genital HIV shedding and reinfection risk. Pregnancy does not eliminate the need for treatment when infection is symptomatic or otherwise clinically indicated, but medication decisions should follow pregnancy-specific guidance. ^{[1] [2] [3]}

The care pathway is to test rather than diagnose from discharge appearance alone, treat with an effective oral nitroimidazole regimen, test for other STIs, manage recent partners, pause sexual activity until treatment is complete and arrange recommended retesting. Persistent cases require assessment for reinfection and resistance. ^{[1] [2]}

When to seek urgent medical care

Seek prompt care for fever with pelvic pain, severe lower-abdominal pain, pregnancy with concerning symptoms, testicular swelling or severe systemic illness. Those features suggest another diagnosis or complication beyond uncomplicated trichomoniasis. ^{[1] [2]}

Sources

1. CDC — Trichomoniasis — STI Treatment Guidelines
2. CDC — About Trichomoniasis
3. WHO — Sexually transmitted infections — fact sheet

This article is based on trusted medical sources and is awaiting clinician review. It is not a substitute for personalized medical advice.