Trichomoniasis is a common sexually transmitted infection (STI) caused by the single-celled parasitic protozoan, Trichomonas vaginalis. It is the most prevalent curable STI globally, affecting millions annually. While often asymptomatic, the infection can still be transmitted and lead to complications if left untreated. Understanding the testing landscape is key to effective diagnosis and management.
Standard Inclusion of Trichomoniasis Testing
Testing for Trichomonas vaginalis is often not automatic, unlike chlamydia and gonorrhea, which are frequently bundled in routine screenings due to public health mandates. Many standard STI panels focus on a core group of infections, such as HIV, syphilis, chlamydia, and gonorrhea, omitting trichomoniasis unless specifically requested.
This omission often stems from a reliance on older, less sensitive testing methods that were unsuitable for widespread asymptomatic screening. Consequently, many healthcare providers only order a trichomoniasis test if a patient presents with specific symptoms, such as unusual discharge or genital irritation, or if they are considered high-risk. However, some specialized clinics now offer expanded STI panels that include the test. Routine screening is more commonly recommended for pregnant women and individuals living with HIV due to the heightened risk of complications.
Specific Diagnostic Methods
Saline Wet Mount
The older, point-of-care method is the saline wet mount, where a swab is mixed with saline and examined under a microscope. This method relies on the direct visualization of the motile parasite, offering immediate results. The wet mount technique has low sensitivity, often ranging from 44% to 68%, meaning it frequently misses infections. The sample must also be examined quickly—within minutes—to ensure the parasite is still motile, which can be impractical in many clinical settings.
Nucleic Acid Amplification Tests (NAATs)
Due to the limitations of the wet mount, current guidelines favor the use of Nucleic Acid Amplification Tests (NAATs). NAATs are considered the gold standard for diagnosis because of their superior sensitivity and specificity, often exceeding 95%. These molecular tests detect the parasite’s genetic material (T. vaginalis DNA). NAATs can be performed on various sample types, including vaginal swabs, cervical specimens, and urine, making them highly effective for screening asymptomatic individuals. Rapid antigen tests and culture are also available but are generally less sensitive than NAATs.
Treatment and Importance of Prompt Diagnosis
Once a diagnosis of trichomoniasis is confirmed, the infection is curable with a single course of oral antibiotics, specifically nitroimidazole drugs like metronidazole or tinidazole. The standard treatment regimen often involves a single, high dose of 2 grams of metronidazole or tinidazole. For women, a multidose regimen, such as 500 milligrams of metronidazole taken twice daily for seven days, may be prescribed, as it has demonstrated a higher cure rate in some studies.
Treating all sexual partners simultaneously is necessary to prevent reinfection and curb the ongoing spread of the parasite. Patients are advised to abstain from sexual activity until both they and their partner have completed the full course of treatment and all symptoms have resolved. Failure to promptly diagnose and treat the infection carries significant public health implications.
The presence of T. vaginalis causes inflammation in the genital tract, which is associated with an increased risk of acquiring and transmitting HIV. In pregnant individuals, an untreated trichomoniasis infection is linked to adverse outcomes, including premature rupture of membranes, preterm delivery, and low birth weight in infants. Because reinfection is common, all women treated for trichomoniasis are advised to undergo a “test of cure” using NAATs within three months of their initial treatment.