Trichomoniasis is a common, curable sexually transmitted infection (STI) caused by the protozoan parasite, Trichomonas vaginalis. While the infection often affects the urogenital tract, its diagnosis can be challenging due to varied or absent symptoms. Urine microscopy offers a quick, albeit less sensitive, method for detecting this organism, particularly when a genital swab is not immediately feasible. This diagnostic approach relies on the laboratory technician’s ability to recognize the parasite’s distinct characteristics in a prepared urine sample.
Understanding Trichomoniasis
The infection is primarily transmitted through sexual contact, where the T. vaginalis parasite passes between partners, residing in the lower genital tract of women and the urethra and prostate of men. Trichomoniasis has one of the highest annual incidences of non-viral STIs globally. Many individuals remain completely asymptomatic, which complicates efforts to contain its spread and makes testing a significant public health measure.
For women, symptomatic infection often involves a thin, frothy, or purulent vaginal discharge that may be yellow-green and possess a foul or “fishy” odor. This is frequently accompanied by irritation, burning, or soreness of the genitals, along with pain during urination or sexual intercourse. Men are more likely to be asymptomatic, but when symptoms do occur, they can include itching or irritation inside the penis, discharge, or a burning sensation following urination or ejaculation.
Untreated trichomoniasis can lead to urogenital tract inflammation, which may increase the risk of acquiring or transmitting other STIs, including HIV. The infection is also linked to adverse pregnancy outcomes, such as preterm delivery and low birth weight. Testing a urine sample is a logical and non-invasive collection method because the infection can reside in the urethra of both sexes.
Identifying the Parasite in Urine
Identification relies on examining a wet mount preparation of spun urine sediment under a microscope. After the sample is centrifuged, the concentrated sediment is placed on a slide with a saline solution to keep the organism viable. A trained technician then scans the field for the characteristic appearance and movement of the T. vaginalis trophozoite.
The parasite is a single-celled protozoan, typically exhibiting a pyriform, or pear-like, shape and ranging in size from 7 to 30 micrometers. The defining feature for microscopic diagnosis is the presence of four anteriorly directed flagella and an undulating membrane, which power its movement. This propulsive apparatus gives the organism its uniquely erratic, rapid, and non-directional “jerky” motility.
The presence of this active, motile organism immediately confirms a positive diagnosis and allows for prompt treatment initiation. However, the specimen must be examined quickly, as the organism loses motility and viability shortly after collection, which can lead to a false-negative result. Without the distinct movement, the parasite is difficult to distinguish from epithelial cells or white blood cells present in the urine sediment.
Accuracy of Urine Testing
While quick and non-invasive, diagnosis based on the wet mount of urine sediment has significant limitations in sensitivity compared to other methods. The traditional wet mount technique has a reported sensitivity range as low as 38% to 60%, meaning it fails to detect the infection in a substantial number of infected individuals. This low sensitivity is due to the parasite’s requirement for viability and motility, as well as the low concentration of organisms in some urine samples.
For women, urine microscopy is generally less effective than examining a vaginal swab, as the concentration of parasites is often higher in the vaginal fluid. Testing a urine sample is a particularly valuable screening tool for men, however, because the organism primarily colonizes the urethra and prostate, making urine a more accessible specimen for initial testing.
If a person has strong symptoms or a known exposure, a negative wet mount should be followed up with a more sensitive test, such as a Nucleic Acid Amplification Test (NAAT). NAAT detects the parasite’s genetic material and is considered the most sensitive diagnostic option available, regardless of the sample type.
Treatment and Long Term Management
Once the diagnosis is confirmed, the infection is highly curable with oral antibiotic medication. Standard treatment involves a course of either metronidazole or tinidazole, which are highly effective against this protozoan parasite. Treatment is typically administered as a single, high dose or a lower dose taken twice daily over seven days.
A fundamental component of management is the simultaneous treatment of all recent sexual partners, even if they are asymptomatic. This concurrent partner therapy prevents the “ping-pong” effect, where the infection is passed back and forth, leading to reinfection.
Patients are advised to abstain from sexual activity until both they and their partners have completed the full course of medication and all symptoms have fully resolved, which typically takes about one week. Follow-up testing, known as a test of cure, is recommended for women three weeks to three months after treatment to ensure the infection has been completely eradicated.