Trikomoniasis

01Pathophysiology

Trichomonas vaginalis is an anaerobic, flagellated protozoan that infects the squamous epithelium of the urogenital tract. It does not have a cyst form, which means it is transmitted exclusively through direct mucosal contact during sexual intercourse and cannot survive long in the environment.

Once the organism attaches to the vaginal epithelium, it causes direct cytotoxic damage through contact-dependent mechanisms and the release of proteolytic enzymes. This triggers a robust inflammatory response with heavy neutrophil infiltration. The intense inflammation explains the purulent, frothy discharge and the punctate hemorrhages on the cervix that produce the classic strawberry cervix appearance. The organism also disrupts the normal vaginal flora and raises the vaginal pH above 4.5 by consuming glycogen and altering the lactobacillus-dominant environment.

The frothy nature of the discharge is attributed to gas production by co-existing anaerobic bacteria that thrive once the vaginal ecosystem is disrupted. This is why the discharge has a foul odor that can mimic bacterial vaginosis, a common source of confusion on exams.

In men, the infection is usually asymptomatic or causes mild urethritis. This is clinically important because untreated male partners serve as a reservoir for reinfection, making simultaneous partner treatment essential.

A high-yield pregnancy connection: trichomoniasis in pregnant women is associated with preterm rupture of membranes and preterm delivery, which is why screening and treatment are important in symptomatic pregnant patients.

02Classification and Clinical Manifestation

The key teaching point is that the classic vignette will describe a sexually active woman with malodorous frothy discharge and a strawberry cervix. If you see this combination, trichomoniasis should be at the top of your differential.

03Diagnostic Workup

Best Initial Test: In a resource-available clinical setting, NAAT is now recommended by the CDC as the preferred diagnostic method due to its superior sensitivity (3 to 5 times more sensitive than wet mount). However, in a classic exam vignette that describes a clinic performing an in-office workup, the wet mount with saline preparation remains the most commonly tested "best initial test," because the question is assessing whether you know to look for motile trichomonads under the microscope.

Most Accurate Test: NAAT is the gold standard for sensitivity and is the confirmatory test when wet mount is negative but clinical suspicion remains high. Wet mount sensitivity is only around 60-70%, meaning a negative wet mount does not rule out the disease.

A critical exam pearl: the wet mount must be examined immediately after collection because the trichomonads lose motility quickly at room temperature. If the vignette mentions a delayed specimen or a non-motile organism, consider that the sensitivity of the wet mount has been compromised and NAAT should be ordered.

Vaginal pH > 4.5 is expected but is not discriminatory on its own, since bacterial vaginosis and atrophic vaginitis also elevate vaginal pH. It serves as a supporting clue, not a standalone diagnostic criterion.

If trichomonads are incidentally found on a Pap smear, the result should be confirmed with NAAT before treating, because Pap has a notable false-positive rate for this organism.

04Management and Treatment

Acute Management Logic: The "next best step" when a sexually active woman presents with frothy green discharge and motile trichomonads on wet mount is to prescribe metronidazole 500 mg twice daily for 7 days and arrange treatment for all sexual partners. In women, the multi-dose regimen is preferred over the single 2 g dose because randomized trials showed higher cure rates with the 7-day course.

For men, the single 2 g dose of metronidazole is sufficient because the organism is easier to eradicate from the male urethra.

Important Contraindication: Patients must be counseled to avoid alcohol during metronidazole therapy and for at least 48 hours after completing treatment (72 hours for tinidazole) due to the disulfiram-like reaction causing nausea, vomiting, and flushing.

Pregnancy Considerations: Metronidazole is considered safe across all trimesters. Symptomatic pregnant women should be treated to reduce the risk of adverse pregnancy outcomes. The 7-day regimen is used, identical to the non-pregnant regimen.

Follow-up: Retesting is recommended at 3 months after treatment to detect reinfection, which is common. Patients should abstain from intercourse until both they and their partners have completed treatment and are asymptomatic.

05Differential Diagnosis and Distractors

06Traps and High-Yield Pearls

The most common way students lose points on trichomoniasis questions falls into three categories.

First, confusing the discharge characteristics across vaginitis types. The frothy, yellow-green, foul-smelling discharge with an elevated pH can overlap with bacterial vaginosis in a student's mind. The discriminating feature is the inflammatory nature of trichomoniasis (many WBCs, motile flagellated organisms) versus the non-inflammatory discharge of BV (clue cells, few WBCs). If the vignette describes frothy green discharge with a strawberry cervix, the answer is trichomoniasis regardless of a positive whiff test.

Second, choosing single-dose metronidazole for women. An older recommendation used a single 2 g dose for both sexes. Current CDC guidelines recommend the 7-day course (500 mg twice daily) for women because it achieves higher cure rates. The single dose is reserved for men. If the question asks for the best treatment for a woman, choose the 7-day regimen.

Third, forgetting partner treatment. A vignette describing a woman with recurrent trichomoniasis despite appropriate therapy is testing whether you recognize the need for simultaneous treatment of sexual partners. The "next best step" in a recurrence scenario is to confirm and ensure partner treatment before escalating to higher-dose regimens.

A final pearl: if a Pap smear incidentally reports trichomonads, the next step is confirmatory NAAT testing, not empiric treatment, because Pap smear has a notable false-positive rate for this organism. This is a classic "next best step" question.