Trichomoniasis is infection of the vagina or male genital tract with Trichomonas vaginalis. It can be asymptomatic or cause urethritis, vaginitis, or occasionally cystitis, epididymitis, or prostatitis. Diagnosis is by microscopic examination of vaginal or prostatic secretions or by urethral culture. Patients and sex partners are treated with metronidazole.
T. vaginalis is a flagellated, sexually transmitted protozoan that more often infects women (about 20% of women of reproductive age) than men. Infection may be asymptomatic in either sex, but asymptomatic is the rule for men. In men, protozoa may persist for long periods in the GU tract without causing symptoms; thus, protozoa may be transmitted unwittingly to sex partners. Trichomoniasis may account for up to 5% of nongonococcal, nonchlamydial urethritis in men in some areas. Co-infection with gonorrhea and other sexually transmitted diseases (STDs) is common.
Symptoms and Signs
In women, symptoms range from none to copious, yellow-green, frothy vaginal discharge with soreness of the vulva and perineum, dyspareunia, and dysuria. Asymptomatic infection may become symptomatic at any time as the vulva and perineum become inflamed and edema develops in the labia. The vaginal walls and surface of the cervix may have punctate, red “strawberry” spots. Urethritis and possibly cystitis may also occur.
Men are usually asymptomatic; however, sometimes urethritis results in a discharge that may be transient, frothy, or purulent or that causes dysuria and frequency, usually early in the morning. Often, urethritis is mild and causes only minimal urethral irritation and occasional moisture at the urethral meatus, under the foreskin, or both. Epididymitis and prostatitis are rare complications.
Trichomoniasis is suspected in women with vaginitis, in men with urethritis, and in their sex partners. Suspicion is high if symptoms persist after patients have been evaluated and treated for other infections such as gonorrhea and chlamydial, mycoplasmal, and ureaplasmal infections.
In women, diagnosis is based on clinical criteria and in-office testing. Vaginal secretions are obtained from the posterior fornix. The pH is measured. Secretions are then placed on 2 slides; they are diluted with 10% K hydroxide on one slide (KOH wet mount) and with 0.9% NaCl on the other (saline wet mount). For the whiff test, the KOH wet mount is checked for a fishy odor, which results from amines produced in trichomonas vaginitis or bacterial vaginosis. The saline wet mount is examined microscopically as soon as possible to detect trichomonads, which can become immotile and more difficult to recognize within minutes after slide preparation. (Trichomonads are pear-shaped with flagella, often motile, and average 7 to 10 μm—about the size of WBCs—but occasionally reach 25 μm.) If trichomoniasis is present, numerous neutrophils are also present.
If results are inconclusive, cultures, which are more sensitive than microscopy, are done. Trichomoniasis is also commonly diagnosed when a Papanicolaou test is done.
In men, microscopy of urine is insensitive, although occasionally organisms are visible in a first-voided morning specimen or a centrifuged specimen. Cultures of urine and urethral swabs are more sensitive.
As with diagnosis of any STD, patients with trichomoniasis should be tested to exclude other common STDs such as gonorrhea and chlamydial infection.
Metronidazole or tinidazole 2 g po in a single dose cures up to 95% of women if sex partners are treated simultaneously. Effectiveness of single-dose regimens in men is not as clear, so treatment is typically with metronidazole or tinidazole 500 mg bid for 5 to 7 days. IV metronidazole cures some women when repeated oral doses are ineffective.
Metronidazole may cause leukopenia, disulfiram-like reactions to alcohol, or candidal superinfections. It is relatively contraindicated during early pregnancy, although it may not be dangerous to the fetus after the 1st trimester. Tinidazole has not been established as safe during pregnancy and so is not used.
Sex partners should be screened and treated for trichomoniasis and other STDs. If poor adherence to follow-up is likely, treatment can be initiated in sex partners of patients with documented trichomoniasis without confirming the diagnosis in the partner.
Last full review/revision November 2008 by J. Allen McCutchan, MD, MSc